Transition-metal-free conversion of lignin model compounds to high-value aromatics: Scope and chemoselectivity

Article abstract of DOI:10.1039/c8gc01886c

An efficient and straightforward reaction protocol for the conversion of lignin model compounds was developed based on a simple system consisting of a base, oxygen, and a green solvent under mild conditions in the absence of metals. This protocol was successfully applied to the cleavage of both 'β-O-4' dimeric and trimeric compounds, and a controlled selective degradation was achieved depending on the bond type. The feasibility of this method to provide aromatic compounds in high yields from lignin by a sequential oxidative dehomologation reaction was clearly demonstrated.

Full text of DOI:10.1039/c8gc01886c

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ISSN 1463-9262
CRITICAL REVIEW
G. Chatel et al.
Heterogeneous catalytic oxidation for lignin valorization into valuable
chemicals: what results? What limitations? What trends?
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Transition-metal-free, conversion of lignin model compounds to
high-value aromatics: scope and chemoselectivity
Received 00th January 20xx,
Accepted 00th January 20xx
Tae Woo Lee and Jung Woon Yang*
DOI: 10.1039/x0xx00000x
An efficient and straightforward reaction protocol for the conversion of lignin model compounds was developed, based on
a simple system consisting of a base, oxygen, and green solvent under mild conditions in the absence of metals. This
protocol was successfully applied to the cleavage of both ‘β-O-4’ dimeric and trimeric compounds, and a controlled
selective degradation was achieved depending on the bond type. The feasibility of this method to provide aromatic
compounds in high yields from lignin by sequential oxidative dehomologation reaction was clearly demonstrated.
www.rsc.org/
by switching the catalyst from
a ruthenium-based to
Introduction
vanadium-based complex through oxidative Cα-Cβ and Cβ-O/Cγ-
O bond cleavages, respectively [Schemes (1a)6k and (1b)6l].
Metal-free reactions were also reported in the literatures;7
In recent years, mankind has become increasingly interested in
biomass as natural energy resource, especially in view of the
depletion of fossil fuels caused by injudicious use and related
environmental impact.1 Among biomass materials, non-food-
based lignocellulosic biomass, which is composed of three
types of polymers [cellulose, hemicellulose (carbohydrate
polymer), and lignin (an aromatic polymer)],2 has been
receiving much attention, especially after being identified as
one of the most convenient renewable resources for the
production of biofuels and bio-chemicals through the bio-
refinery approach.3 Lignin is the third most abundant polymer
in nature, and possesses an irregular polymeric structure
based on aromatic rings connected through different types of
bonds. Studies on the fragmentation of lignin at the β-O-4
linkage, which is the most dominant unit in three-dimensional
biopolymers (e.g., soft wood: 40-50%; hard wood: 60%, Figure
1),4 have been steadily emerging because of its synthetic
relevance as a potential supplier of aromatics and promising
alternative source of hydrocarbon fuels.5 To gain better
understanding of the degradation pattern of lignin, several
studies have focused on the development of β-O-4 dimeric
lignin model compounds bearing methoxy and hydroxyl
substituents at diverse positions of the arene rings, which
represent the principal substructures of lignin.6-7
however,
pre-functionalisation
(e.g.,
oxidation
and
formylation-elimination or diesterification-elimination) of the
starting materials was indispensable to produce the desired
products via oxidative Cγ-O/Cβ-O and Cβ-O/ Cβ-Cγ bond
cleavages [Schemes (1c)7a and (1d)7c-d]. Although the
aforementioned
reactions
produced
the
desired
fragmentation, issues remained since the position and type of
substituents on the aromatic rings could drastically affect the
chemical yield of the product in some cases.6k Therefore, a full
investigation of the reaction scope is highly desirable.
OMe
OH
OMe
β
HO
O
OH
O
O
4
α
O
OH
OH
OH
OH
OMe
O
O
OMe
OH
OH
MeO
O
OMe
OMe
(lignin model compound
β -O-4)
Figure 1 Schematic representation of lignin and the corresponding
compound used in this study.
β-O-4 model
Herein, we describe a simple transition-metal-free base-
promoted oxidative dehomologation of dilignol model
compounds to the corresponding aromatic alcohols and acids,
which represent an unprecedented product pattern, under an
oxygen atmosphere (Scheme 2). In contrast to previous
reports, our protocol allows for the use of a simple reaction
procedure and the production of high-value aromatics with an
extremely high chemoselectivity without need for pre-
functionalization.
Recently, direct and indirect methods for the oxidative
fragmentation of lignin model compounds have been
developed, leading to the generation of multifarious products
under different reaction conditions (Scheme 1). In the case of
transition metal catalysis,6 different products were obtained
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Journal Name
Scheme
1
Previous
reports
on
the
fragmentation
of
lignin
model
compound.
>99% was easily reached in HMPA, a greener solvent is
preferable since HMPA is known to be very hazardous due to
its carcinogenicity. Therefore, in order to avoid the use of
HMPA, various solvents were screened, and the majority gave
excellent conversions except for DMF (Table 1, entries 2-10).
However, THF, diethyl ether, and hydrocarbon-type solvents
were not used in this study due to their intrinsic flammable or
explosive properties. Although comparable results were
obtained in CH2Cl2, this chlorinated solvent was also excluded
owing to its potential negative effects on human health and
environment. It was anticipated that t-BuOH might offer a
higher potential to serve as alternative green solvent in this
study due to its relatively low toxicity and flammability as well
as high oxygen uptake ability compared to other solvents.
Indeed, a maximum conversion of >99% was achieved when
conducting the reaction in t-BuOH at 30 oC.
Scheme 2 Current work on the fragmentation of lignin model compound.
Results and discussion
We began our study by examining the transformation of the as
a basic lignin model compound 2-phenoxy-1-phenylpropane-
1,3-diol
(1a) to high-value aromatics under conditions
previously established for the oxidative dehomologation of
alcohols utilising a NaOtBu-O2 system.8 Phenol 2a and benzoic
acid 3a were obtained as fragmentation product in >99%
conversion at room temperature when NaOtBu and HMPA
(hexamethylphosphoramide) were tested as base/promotor
and solvent, respectively. Although a chemical conversion of
The scope of the oxidative dehomologation of lignin model
compounds was then explored. First, we assessed 2-phenoxy-
1-
2 | J. Name., 2012, 00, 1-3
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phenylpropane-1,3-diol (1a) bearing methoxy group at ortho-, The current method shows good tolerance toward the position
meta-, and para-position on both red and blue coloured of substituent on arene, which is one of the drawbacks of
arenes.
existing technology for oxidative cleavage of lignin model
compounds, and corresponding products (such as phenol and
benzoic acid derivatives) were achieved in excellent yields and
chemoselectivities. We then investigated the influence of
hydroxyl groups on β-O-4 model compounds (1u and 1v).
Benzoquinones were mostly obtained by previous reports,6a-
Table 1. Screening of parameters for oxidative cleavage of lignin model compounda
d,6m,7e
whereas guaiacol 2b and vanillic acid 3f as major
products were obtained with small quantities of vanillin and
coniferyl aldehyde under our optimum conditions, in case of
Entry
1
Base (equiv)
NaOtBu (4)
NaOtBu (4)
NaOtBu (4)
NaOtBu (4)
NaOtBu (4)
NaOtBu (4)
NaOtBu (4)
NaOtBu (4)
NaOtBu (4)
NaOtBu (4)
NaOtBu (4)
Solvent
HMPA
Temp (oC)
Conv. (%)b
>99
>99
>99
>99
>99
>99
>99
>99
90
1u
.
25
25
25
25
25
25
25
25
25
30
30
Based on our previous 18O-labeling experiments on the
oxidative cleavage reactions of alcohols8-9 or direct oxidation
of allylic alcohol10, the reaction mechanism is proposed as
shown in Scheme 3. The initial step involves alcohol oxidation
as usual; referring to our previous reports on the isolation of
key intermediates, such as 1,2-diketone9 or α,β-unsaturated
aldehyde10 in extremely poor yields from the oxidative
cleavage reaction of 1,2-diol or the oxidation of primary allylic
alcohol under the NaOtBu-O2 system, respectively. According
to the general oxidation trend, primary alcohol is normally
more reactive than secondary alcohol due to steric issues.
2
THF
3
Et2O
4
Pentane
Cyclohexane
CH2Cl2
5
6
7
Toluene
Benzene
DMF
8
9
10
11c
t-BuOH
t-BuOH
>99
0
a General conditions: 1a (0.5 mmol), NaOtBu (4 equiv), solvent (2 mL), O2 (1 atm).
Determined by 1H NMR spectroscopy using benzyl benzoate as an internal
b
standard. c Anaerobic condition.
Table 2. Reaction scopea
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Journal Name
Products
(2+3)
Entry
Substrate
A
B
C
D
E
F
Conv. (%) Yields of 2b:3c (%)
1
1a
1b
1c
1d
1e
1f
H
H
H
H
H
H
2a + 3a
2a + 3b
2a + 3c
2a + 3d
2b + 3a
2b + 3b
2b + 3c
2b + 3d
2c + 3a
2c + 3b
2c + 3c
2c + 3d
2d + 3a
2d + 3b
2d + 3c
2d + 3d
2a + 3e
2b + 3e
99
86
99
97
83
78
98
91
96
67
98
97
83
47
92
80
93
95
87:94
71:74
80:97
84:86
65:68
69:62
69:70
77:80
82:86
63:60
85:95
84:89
58:79
44:38
63:86
60:68
75:90
78:87
2
H
H
H
OMe
H
H
H
3
H
H
H
OMe
H
H
4
H
H
H
H
OMe
H
5
OMe
OMe
OMe
OMe
H
H
H
H
H
6
H
H
OMe
H
H
H
7
1g
1h
1i
H
H
OMe
H
H
8
H
H
H
OMe
H
9
OMe
OMe
OMe
OMe
H
H
H
H
10
11
12
13
14
15
16
17
18
1j
H
H
OMe
H
H
H
1k
1l
H
H
OMe
H
H
H
H
H
OMe
H
1m
1n
1o
1p
1q
1r
H
OMe
OMe
OMe
OMe
H
H
H
H
H
OMe
H
H
H
H
H
OMe
H
H
H
H
H
OMe
OMe
OMe
H
H
H
OMe
OMe
OMe
OMe
OMe (A’)
OMe
OMe (A’)
OMe
H
H
H
19
1s
H
H
H
H
H
2e + 3a
87
73:83
20
1t
H
H
H
H
H
H
H
H
H
OMe
OMe
OH
2e + 3e
2b + 3f
2b + 3g
81
88
86
73:74
65:30
56:28
21d
22 d
1u
1v
OMe
OMe
OMe
OH
OMe (G)
a
c
d
General conditions: 1 (0.5 mmol), NaOtBu (4 equiv), t-BuOH (2 mL), O2 (1 atm), 30 oC. b Isolated yield. Determined by 1H NMR spectroscopy. Using 5 equiv. of
NaOtBu in 2.5 mL of t-BuOH.
Scheme 3 Proposed mechanism.
In this study, however, unselective oxidation of either primary cannot be excluded since both primary and secondary alcohols
or secondary alcohol incorporating lignin model compound
1
co-exist in a single molecule and excess amounts of NaOtBu (4
4 | J. Name., 2012, 00, 1-3
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equiv.), used as oxygen carrier, are added. For these reasons,
two possible reaction pathways are postulated.
In path I, oxidation of the primary alcohol to aldehyde involves
the first step, where, initially, selective deprotonation of the
primary alcohol incorporating lignin model compound 1r by
NaOtBu and hydride transfer from the α-carbon of primary
alcohol to molecular oxygen produce aldehyde
hydroperoxide anion . Treatment of aldehyde 4 with NaOtBu
lead to nucleophilic enolate
afford 1,2-dioxetan-3-olate (
4 and
5
6
that attacks molecular oxygen to
) via intramolecular nucleophilic
8
addition of peroxyanion to the carbonyl carbon
ring-opening of due to its extremely strained ring structure
takes place to give α-hydroxy ester . Secondary alcohol
moiety in is readily oxidised to ketone 10 via hydride transfer
7. Subsequent
8
Scheme 4 Transformation of trimeric lignin model compound.
9
9
from the α-carbon of secondary alcohol to molecular oxygen
after deprotonation of alcohol with base. The resulting α-
ketoester 10 undergoes selective nucleophilic attack by
Conclusions
In summary, we have demonstrated an efficient lignin model
hydroperoxide anion
5 to give intermediate 11. Mixed
degradation
reaction
by
consecutive
oxidative
anhydride 12 as a transient intermediate is formed via Baeyer-
Villiger mechanism with acyl group migration,11 leading the
desired products (guaiacol 2b and veratric acid 3e) after
further nucleophilic substitution reaction with the liberating
hydroxide ion and simple acid work-up.
dehomologation utilising NaOtBu-O2 system. The advantages
of current protocols include (i) the use of eco-friendly oxidising
agent and employment of environmentally sound solvent t-
BuOH (ii) showing highly chemoselective degradation to high-
value chemical feedstocks (e.g., phenols and benzoic acids).
Further efforts to expand the application of the reaction with
organosolv lignin or industrial waste are underway in our
laboratory.
In path II, oxidation of the secondary alcohol to ketone is
involved in the first step; similarly in primary alcohol oxidation,
this possible reaction pathway also presumably produces the
highly strained 1,2-dioxetan-3-olate (16) via the formation of
ketone 13, enolate 14, and peroxyanion-tethered ketone 15
.
Subsequent ring-opening of 16 renders carboxylate in the form
of 3e, which can be converted to the desired product 3e
through the end reaction via simple acid work-up and α-
hydroxy ester 17. Further oxidation of 17 under the NaOtBu-O2
Experimental
General procedure for the synthesis of lignin model
compounds (1a-1v, A): All dimeric lignin model compounds
were prepared according to the previously reported
procedures.13,14
system produces mixed anhydride 20 as
a transient
intermediate. After consecutive deformylation and carbon
dioxide emission, the desired product 2b is obtained via simple
acid work-up.
2-Phenoxy-1-phenylpropane-1,3-diol
(1a)13
:
The
title
compound 1a was synthesized according to general procedure
A and obtained as a white solid. No attempt was made to
1
separate the diastereomer mixture. H NMR (500 MHz, CDCl3,
As described in Scheme 3, aldehyde (
4
)/or ketone (13), α-
18), as
hydroxy esters ( 17), and α-carbonyl esters (10,
9,
25 °C, mixture of diastereoisomers): δ 7.48–7.40 (m, 2H), 7.40–
7.33 (m, 2H), 7.32–7.23 (m, 3H), 6.99–6.95 (m, 1H), 6.95–6.90
(m, 2H); Major δ 5.14–5.10 (m, 1H), 4.44 (dd, J = 9.1, 4.7 Hz,
1H), 3.99–3.92 (m, 1H), 3.89–3.84 (m, 1H), 2.77 (d, J = 3.6 Hz,
1H), 2.15 (t, J = 6.4 Hz, 1H); Minor δ 5.06 (dd, J = 6.7, 3.2 Hz,
1H), 4.43–4.41 (m, 1H), 3.83–3.78 (m, 1H), 3.62–3.55 (m, 1H),
2.80 (d, J = 3.3 Hz, 1H), 1.77 (dd, J = 7.3, 5.4 Hz, 1H) ppm;
13C{1H}NMR (126 MHz, CDCl3, 25 °C, mixture of
reactive transient species, may be present in the reaction
mixture, since these intermediates rapidly react with the
hydroperoxide anion (
5), which is one of the most reactive
chemical species, to give the desired products (2b and 3e
)
without detection of intermediate(s) via the spot-to-spot
manner.
To our delight, trimeric lignin model compound6d,6l,12
(21) is
also applicable for oxidative dehomologation reaction under
our optimum conditions, rendering value-added aromatics
(mainly phenol and benzoic acid derivatives) that have not
been reported so far (Scheme 4).
diastereoisomers): Major
δ 157.50 (CAr–O), 140.17 (CAr),
129.67 (CArH), 128.54 (CArH), 127.99 (CArH), 126.20 (CArH),
121.92 (CArH), 116.58 (CArH), 81.81 (CH), 74.05 (CH), 61.19
(CH2); Minor δ 157.52 (CAr–O), 139.57 (CAr), 129.74 (CArH),
128.61 (CArH), 128.33 (CArH), 126.93 (CArH), 122.05 (CArH),
116.51 (CArH), 83.04 (CH), 73.94 (CH), 61.04 (CH2) ppm.
1-(2-Methoxyphenyl)-2-phenoxypropane-1,3-diol (1b)
: The
title compound 1b was synthesized according to general
procedure A. White solid; mp = 94.8–95.5 °C; yield = 92%. No
attempt was made to separate the diastereomer mixture. 1H
NMR (500 MHz, CDCl3, 25 °C, mixture of diastereoisomers): δ
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7.52–7.45 (m, 1H), 7.30–7.21 (m, 3H), 7.07–6.83 (m, 5H); 114.03 (CArH), 83.18 (CH), 73.63 (CH), 61.09 (CH2), 55.30 (OCH3)
Major δ 5.38 (t, J = 4.7 Hz, 1H), 4.70 (dd, J = 9.5, 4.1 Hz, 1H), ppm.
3.98–3.91 (m, 1H), 3.87 (s, 3H), 3.80–3.75 (m, 1H), 3.10 (d, J = 2-(2-Methoxyphenoxy)-1-phenylpropane-1,3-diol (1e)17: The
5.3 Hz, 1H), 2.21 (dd, J = 7.4, 5.7 Hz, 1H); Minor δ 5.33 (t, J = title compound 1e was synthesized according to general
5.8 Hz, 1H), 4.51 (dt, J = 6.4, 4.1 Hz, 1H), 3.85–3.81 (m, 1H), procedure A and obtained as a white solid. No attempt was
3.86 (s, 3H), 3.69–3.61 (m, 1H), 3.06 (d, J = 5.3 Hz, 1H), 2.23– made to separate the diastereomers mixture. 1H NMR (500
2.21 (m, 1H) ppm; 13C{1H}NMR (126 MHz, CDCl3, 25 °C, mixture MHz, CDCl3, 25 °C, mixture of diastereoisomers): δ 7
.47–7.31
of diastereoisomers): Major δ 157.78 (CAr–O), 156.03 (CAr–O), (m, 4H), 7.30–7.26 (m, 1H), 7.11–7.02 (m, 1H), 6.93 (m, 3H);
129.54 (CArH), 128.85 (CArH), 127.68 (CArH), 127.47 (CAr), 121.49 Major δ 5.07–5.03 (m, 1H), 4.19 (ddd, J = 6.0, 4.5, 3.4 Hz, 1H),
(CArH), 121.06 (CArH), 116.22 (CArH), 110.29 (CArH), 79.19 (CH), 3.94–3.90 (m, 1H), 3.88 (s, 3H), 3.67–3.60 (m, 1H), 3.54 (d, J =
70.24 (CH), 61.59 (CH2), 55.33 (OCH3); Minor δ 158.52 (CAr–O), 3.4 Hz, 1H), 2.75 (dd, J = 7.8, 5.3 Hz, 1H); Minor δ 5.07–5.03
155.95 (CAr–O), 129.58 (CArH), 129.15 (CArH), 128.07 (CAr), (m, 1H), 4.08–4.03 (m, 1H), 3.91 (s, 3H), 3.68 (d, J = 2.1 Hz, 1H),
127.54 (CArH), 121.72 (CArH), 121.31 (CArH), 116.63 (CArH), 3.67–3.60 (m, 1H), 3.48 (ddd, J = 12.4, 8.3, 4.0 Hz, 1H), 2.77–
110.69 (CArH), 82.73 (CH), 69.57 (CH), 61.85 (CH2), 55.66 (OCH3) 2.73 (m, 1H) ppm; 13C{1H}NMR (126 MHz, CDCl3, 25 °C, mixture
ppm. HRMS (FAB+) m/z: [M+H]+ calcd for C16H18O4 274.1205, of diastereoisomers): Major δ 151.74 (CAr–O), 146.79 (CAr–O),
found 274.1213. IR: 3467, 2982, 2838, 1602, 1494, 1466, 1243, 139.78 (CAr), 128.44 (CArH), 127.70 (CArH), 126.03 (CArH), 124.37
1073, 1057, 1028 cm-1.
(CArH), 121.66 (CArH), 121.26 (CArH), 112.24 (CArH), 87.52 (CH),
1-(3-Methoxyphenyl)-2-phenoxypropane-1,3-diol (1c)
:
The 72.91 (CH), 60.59 (CH2), 55.91 (OCH3) ppm; Minor δ 151.35
title compound 1c was synthesized according to general (CAr–O), 147.58 (CAr–O), 139.63 (CAr), 128.55 (CArH), 128.24
procedure A. White solid; mp = 54.4–56 °C; yield = 89%. No (CArH), 127.14 (CArH), 124.33 (CArH), 121.70 (CArH), 121.17
1
attempt was made to separate the diastereomer mixture. H (CArH), 112.17 (CArH), 89.54 (CH), 74.11 (CH), 61.01 (CH2), 55.91
NMR (500 MHz, CDCl3, 25 °C, mixture of diastereoisomers): δ (OCH3) ppm.
7.31–7.25 (m, 3H), 7.05–6.92 (m, 5H), 6.88–6.81 (m, 1H); 2-(2-Methoxyphenoxy)-1-(2-methoxyphenyl)propane-1,3-diol
Major δ 5.12–5.09 (m, 1H), 4.45 (dd, J = 9.1, 4.8 Hz, 1H), 3.99– (1f): The title compound 1f was synthesized according to
3.92 (m, 1H), 3.90–3.84 (m, 1H), 3.80 (s, 3H), 2.75 (d, J = 3.5 Hz, general procedure A. White solid; mp = 115.3–116.8 °C; yield =
1H), 2.11 (t, J = 6.4 Hz, 1H); Minor δ 5.06–5.00 (m, 1H), 4.44– 92%. No attempt was made to separate the diastereomer
4.41 (m, 1H), 3.83–3.81 (m, 1H), 3.81 (s, 3H), 3.65–3.58 (m, mixture. 1H NMR (500 MHz, CDCl3, 25 °C, mixture of
1H), 2.78 (d, J = 3.3 Hz, 1H), 1.75 (dd, J = 7.1, 5.5 Hz, 1H) ppm; diastereoisomers): δ 7.56–7.52 (m, 1H), 7.30–7.22 (m, 1H),
13C{1H}NMR (126 MHz, CDCl3, 25 °C, mixture of 7.09–6.95 (m, 3H), 6.95–6.87 (m, 2H), 6.86–6.80 (m, 1H);
diastereoisomers): Major δ 159.57 (CAr–O), 157.58 (CAr–O), Major δ 5.32 (t, J = 4.2 Hz, 1H), 4.47 (dt, J = 6.5, 3.8 Hz, 1H),
141.19 (CAr), 129.60 (CArH), 129.40 (CArH), 121.74 (CArH), 118.66 3.97–3.93 (m, 1H), 3.88 (s, 3H), 3.78 (s, 3H), 3.70 (d, J = 4.9 Hz,
(CArH), 116.58 (CArH), 113.23 (CArH), 111.98 (CArH), 81.71 (CH), 1H), 3.66–3.58 (m, 1H), 2.78 (dd, J = 8.0, 5.2 Hz, 1H) ppm;
73.73 (CH), 61.13 (CH2), 55.17 (OCH3); Minor δ 159.59 (CAr-O), Minor δ 5.32–5.29 (m, 1H), 4.21 (dt, J = 7.0, 4.2 Hz, 1H), 3.92–
158.07 (CAr–O), 141.55 (CAr), 129.60 (CArH), 129.45 (CArH), 3.88 (m, 1H), 3.90 (s, 3H), 3.86 (s, 3H), 3.71 (d, J = 4.3 Hz, 1H),
121.80 (CArH), 119.14 (CArH), 116.46 (CArH), 113.64 (CArH), 3.68–3.58 (m, 1H), 2.94 (t, J = 6.9 Hz, 1H) ppm; 13C{1H}NMR
112.33 (CArH), 82.50 (CH), 73.40 (CH), 60.94 (CH2), 55.17(OCH3) (126 MHz, CDCl3, 25 °C, mixture of diastereoisomers): Major δ
ppm. HRMS (FAB+) m/z: [M+H]+ calcd for C16H18O4 274.1205, 155.93 (CAr–O), 151.38 (CAr–O), 147.21 (CAr–O), 128.62 (CAr),
found 274.1209. IR: 3383, 2938, 2836, 1597, 1490, 1237, 1039 127.68 (CArH), 127.40 (CArH), 123.70 (CArH), 121.41 (CArH),
cm-1.
120.97 (CArH), 120.22 (CArH), 112.11 (CArH), 110.12 (CArH),
1-(4-Methoxyphenyl)-2-phenoxypropane-1,3-diol (1d)16: The 84.45 (CH), 69.61 (CH), 61.14 (CH2), 55.89 (OCH3), 55.25
title compound 1d was synthesized according to general (OCH3); Minor δ 156.39 (CAr–O), 151.14 (CAr–O), 148.26 (CAr–
procedure A and obtained as a white solid. No attempt was O), 129.00 (CAr), 128.37 (CArH), 128.06 (CArH), 123.84 (CArH),
made to separate the diastereomer mixture. 1H NMR (500 121.54 (CArH), 121.15 (CArH), 120.92 (CArH), 112.09 (CArH),
MHz, CDCl3, 25 °C, mixture of diastereoisomers): δ 7.40–7.32 110.61 (CArH), 88.60 (CH), 69.26 (CH), 62.19 (CH2), 55.59
(m, 2H), 7.31–7.21 (m, 2H), 7.03–6.93 (m, 1H), 6.93–6.85 (m, (OCH3), 55.25 (OCH3) ppm. HRMS (FAB+) m/z: [M+H]+ calcd for
4H); Major δ 5.04 (dd, J = 4.9, 3.7 Hz, 1H), 4.40 (dd, J = 9.4, 4.6 C17H21O5 304.1311, found 304.1306; IR: 3505, 2975, 2842,
Hz, 1H), 3.94 (ddd, J = 11.1, 6.2, 4.8 Hz, 1H), 3.85 (ddd, J = 12.5, 1590, 1508, 1453, 1259, 1125, 1026 cm-1.
8.4, 5.3 Hz, 1H), 3.79 (s, 3H), 2.75 (d, J = 3.5 Hz, 1H), 2.24 (t, J = 2-(2-Methoxyphenoxy)-1-(3-methoxyphenyl)propane-1,3-diol
6.4 Hz, 1H); Minor δ 5.00 (dd, J = 6.9, 2.9 Hz, 1H), 4.40–4.38 (1g): The title compound 1g was synthesized according to
(m, 1H), 3.80 (s, 3H), 3.82–3.75 (m, 1H), 3.59–3.51 (m, 1H), general procedure A. Sticky solid; mp = 45–46 °C; yield = 87.5%.
2.79 (d, J = 3.0 Hz, 1H), 1.81 (dd, J = 7.3, 5.4 Hz, 1H) ppm; No attempt was made to separate the diastereomer mixture.
13C{1H}NMR (126 MHz, CDCl3, 25 °C, mixture of 1H NMR (500 MHz, CDCl3, 25 °C, mixture of diastereoisomers):
diastereoisomers): Major δ 159.32 (CAr–O), 157.65 (CAr–O), δ 7.30–7.24 (m, 1H), 7.13–6.89 (m, 6H), 6.87–6.78 (m, 1H);
132.40 (CAr), 129.66 (CArH), 127.50 (CArH), 121.87 (CArH), 116.61 Major δ 5.03 (t, J = 3.7 Hz, 1H), 4.19 (ddd, J = 6.1, 4.3, 3.5 Hz,
(CArH), 113.94 (CArH), 81.87 (CH), 73.85 (CH), 61.36 (CH2), 55.30 1H), 3.95 – 3.88 (m, 1H), 3.89 (s, 3H), 3.80 (s, 3H), 3.68 – 3.61
(OCH3); Minor δ 159.60 (CAr–O), 158.09 (CAr–O), 131.66 (CAr), (m, 1H), 3.55 (d, J = 3.3 Hz, 1H), 2.75–2.68 (m, 1H); Minor δ
129.76 (CArH), 128.20 (CArH), 122.03 (CArH), 116.55 (CArH), 5.02–5.00 (m, 1H), 4.09–4.02 (m, 1H), 3.95–3.88 (m, 1H), 3.91
6 | J. Name., 2012, 00, 1-3
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(s, 3H), 3.81 (s, 3H), 3.52–3.48 (m, 1H), 3.53–3.51 (m, 1H), 3.81–3.73 (m, 1H), 3.06 (d, J = 5.3 Hz, 1H), 2.19 (dd, J = 7.4, 5.7
2.77–2.71 (m, 1H) ppm; 13C{1H}NMR (126 MHz, CDCl3, 25 °C, Hz, 1H) ppm; 13C{1H}NMR (126 MHz, CDCl3, 25 °C): δ 160.91
mixture of diastereoisomers): Major δ 159.80 (CAr–O), 151.75 (CAr–O), 158.97 (CAr–O), 156.03 (CAr–O), 129.94 (CArH), 128.85
(CAr–O), 146.76 (CAr–O), 141.39 (CAr), 129.48 (CArH), 124.39 (CArH), 127.67 (CAr), 127.40 (CArH), 121.04 (CArH), 110.28 (CArH),
(CArH), 121.68 (CArH), 121.26 (CArH), 118.29 (CArH), 113.22 108.35 (CArH), 106.83 (CArH), 102.73 (CArH), 79.15 (CH), 70.14
(CArH), 112.23 (CArH), 111.53 (CArH), 87.44 (CH), 72.79 (CH), (CH), 61.56 (CH2), 55.31 (OCH3), 55.30 (OCH3) ppm. HRMS
60.61 (CH2), 55.92 (OCH3), 55.26 (OCH3); Minor δ 159.82 (CAr– (FAB+) m/z: [M+H]+ calcd for C17H21O5 305.1398, found
O), 151.34 (CAr–O), 147.59 (CAr–O), 141.24 (CAr), 129.57 (CArH), 305.1392. IR: 3469, 2943, 2836, 1618, 1490, 1464, 1295, 1245,
124.32 (CArH), 121.71 (CArH), 121.15 (CArH), 119.52 (CArH), 1150, 1065, 1036 cm-1.
113.95 (CArH), 112.41 (CArH), 112.18 (CArH), 89.43 (CH), 74.08 2-(3-Methoxyphenoxy)-1-(3-methoxyphenyl)propane-1,3-diol
(CH), 61.08 (CH2), 55.92 (OCH3), 55.28 (OCH3) ppm. HRMS (1k): The title compound 1k was synthesized according to
(FAB+) m/z: [M+H]+ calcd for C17H21O5 304.1311, found general procedure A. White solid; mp = 66.8–67.0 °C; yield =
304.1308. IR: 3374, 2934, 2834, 1589, 1498, 1457, 1253, 1215, 94%. 1H NMR (500 MHz, CDCl3, 25 °C): δ 7.30–7.26 (m, 1H),
1116, 1042, 1018 cm-1.
7.16 (t, J = 8.2 Hz, 1H), 7.02–6.98 (m, 2H), 6.85–6.77 (m, 1H),
2-(2-Methoxyphenoxy)-1-(4-methoxyphenyl)propane-1,3-diol 6.54 (dd, J = 8.2, 2.3 Hz, 2H), 6.49 (t, J = 2.3 Hz, 1H), 5.13–5.07
(1h)18: The title compound 1h was synthesized according to (m, 1H), 4.43 (dd, J = 9.0, 4.7 Hz, 1H), 3.95 (ddd, J = 11.0, 6.2,
general procedure A and obtained as a white solid. 1H NMR 4.8 Hz, 1H), 3.86 (ddd, J = 12.1, 6.6, 4.0 Hz, 1H), 3.80 (s, 3H),
(500 MHz, CDCl3, 25 °C): δ 7.34 (d, J = 8.6 Hz, 2H), 7.12–7.06 3.76 (s, 3H), 2.78 (d, J = 2.9 Hz, 1H), 2.13 (t, J = 6.4 Hz, 1H)
(m, 1H), 7.02–6.89 (m, 5H), 5.02 (t, J = 3.9 Hz, 1H), 4.18 (dd, J = ppm; 13C{1H}NMR (126 MHz, CDCl3, 25 °C): δ 160.93 (CAr–O),
8.7, 5.2 Hz, 1H), 3.97–3.92 (m, 1H), 3.91 (s, 3H), 3.83 (s, 3H), 159.83 (CAr–O), 158.76 (CAr–O), 141.84 (CAr), 130.08 (CArH),
3.68 (m, 1H), 3.46 (d, J = 3.4 Hz, 1H), 2.78 (dd, J = 7.6, 5.4 Hz, 129.62 (CArH), 118.46 (CArH), 113.40 (CArH), 111.84 (CArH),
1H) ppm; 13C{1H}NMR (126 MHz, CDCl3, 25 °C): δ 159.12 (CAr– 108.48 (CArH), 107.58 (CArH), 103.06 (CArH), 81.81 (CH), 73.91
O), 151.70 (CAr–O), 146.90 (CAr–O), 131.94 (CAr), 127.27 (CArH), (CH), 61.23 (CH2), 55.31 (OCH3), 55.28 (OCH3) ppm. HRMS
124.27 (CArH), 121.63 (CArH), 121.20 (CArH), 113.85 (CArH), (FAB+) m/z: [M+H]+ calcd for C17H21O5 305.1398, found
112.19 (CArH), 87.54 (CH), 72.61 (CH), 60.68 (CH2), 55.90 305.1392. IR: 3283, 2942, 2834, 1600, 1488, 1285, 1194, 1154,
(OCH3), 55.28 (OCH3) ppm.
1092, 1040 cm-1.
2-(3-Methoxyphenoxy)-1-phenylpropane-1,3-diol (1i)
:
The 2-(3-Methoxyphenoxy)-1-(4-methoxyphenyl)propane-1,3-diol
title compound 1i was synthesized according to general (1l): The title compound 1l was synthesized according to
procedure A. White solid; mp = 61.4–62.3 °C; yield = 91.7%. No general procedure A. White solid; mp = 73.5°C; yield = 91.5%.
1
attempt was made to separate the diastereomer mixture. H 1H NMR (500 MHz, CDCl3, 25 °C): δ 7.35 (d, J = 8.6 Hz, 2H), 7.15
NMR (500 MHz, CDCl3, 25 °C, mixture of diastereoisomers): δ (t, J = 8.2 Hz, 1H), 6.89 (d, J = 8.7 Hz, 2H), 6.57–6.49 (m, 2H),
7.47–7.26 (m, 5H), 7.15 (m, 1H), 6.60–6.49 (m, 2H), 6.46 (m, 6.46 (t, J = 2.3 Hz, 1H), 5.10–5.02 (m, 1H), 4.39 (dd, J = 9.4, 4.6
1H), Major δ 5.14–5.08 (m, 1H), 4.41 (dd, J = 9.1, 4.7 Hz, 1H), Hz, 1H), 3.94 (ddd, J = 11.1, 6.2, 4.7 Hz, 1H), 3.86 (ddd, J = 11.0,
3.94 (ddd, J = 11.5, 6.2, 4.7 Hz, 1H), 3.85 (ddd, J = 11.5, 6.2, 3.7 7.6, 4.4 Hz, 1H), 3.80 (s, 3H), 3.76 (s, 3H), 2.70 (d, J = 3.5 Hz,
Hz, 1H), 3.75 (s, 3H), 2.87 (d, J = 3.7 Hz, 1H), 2.23 (t, J = 6.4 Hz, 1H), 2.19 (t, J = 6.4 Hz, 1H) ppm; 13C{1H}NMR (126 MHz, CDCl3,
1H); Minor δ 5.05 (dd, J = 6.6, 3.3 Hz, 1H), 4.40–4.38 (m, 1H), 25 °C): δ 160.91 (CAr–O), 159.35 (CAr–O), 158.87 (CAr–O),
3.82–3.79 (m, 1H), 3.77 (s, 3H), 3.61–3.52 (m, 1H), 2.84 (d, J = 132.36 (CAr), 130.05 (CArH), 127.48 (CArH), 113.96 (CArH), 108.51
3.3 Hz, 1H), 1.85 (dd, J = 7.2, 5.5 Hz, 1H) ppm; 13C{1H}NMR (126 (CArH), 107.49 (CArH), 103.06 (CArH), 81.90 (CH), 73.83 (CH),
MHz, CDCl3, 25 °C, mixture of diastereoisomers): Major δ 61.36 (CH2), 55.30 (OCH3), 55.30 (OCH3) ppm. HRMS (FAB+)
160.92(CAr–O), 158.79 (CAr–O), 140.24 (CAr), 130.07 (CArH), m/z: [M+H]+ calcd for C17H21O5 305.1398, found 305.1386. IR:
128.56 (CArH), 128.00 (CArH), 126.24 (CArH), 108.53 (CArH), 3438, 2963, 2837, 1618, 1593, 1491, 1460, 1253, 1148, 1032,
107.55 (CArH), 103.08 (CArH), 81.89 (CH), 74.07 (CH), 61.24 1010 cm-1.
(CH2), 55.31 (OCH3); Minor δ 160.96 (CAr-O), 159.28 (CAr-O), 2-(4-Methoxyphenoxy)-1-phenylpropane-1,3-diol (1m)
: The
139.66 (CAr), 130.16 (CArH), 128.62 (CArH), 128.33 (CArH), 126.94 title compound 1m was synthesized according to general
(CArH), 108.53 (CArH), 107.58 (CArH), 103.02 (CArH), 83.06 (CH), procedure A. Colorless sticky liquid; yield = 83%. No attempt
1
73.93 (CH), 61.14 (CH2), 55.34 (OCH3) ppm. HRMS (FAB+) m/z: was made to separate the diastereomer mixture. H NMR (500
[M+H]+ calcd for C16H18O4 275.1283, found 275.1278. IR: 3401, MHz, CDCl3, 25 °C, mixture of diastereoisomers): δ 7.48–7.26
2940, 2836, 1600, 1491, 14536, 1283, 1264, 1199, 1150, 1040 (m, 5H), 6.94–6.75 (m, 4H); Major δ 5.12–5.06 (m, 1H), 4.27
cm-1.
(dd, J = 9.2, 4.7 Hz, 1H), 3.97–3.88 (m, 1H), 3.85–3.79 (m, 1H),
2-(3-Methoxyphenoxy)-1-(2-methoxyphenyl)propane-1,3-diol 3.75 (s, 3H), 2.84 (d, J = 3.5 Hz, 1H), 2.22 (t, J = 6.4 Hz, 1H);
(1j): The title compound 1j was synthesized according to Minor δ 5.03 (dd, J = 6.7, 3.1 Hz, 1H), 4.27–4.24 (m, 1H), 3.81–
general procedure A. white solid; mp = 95.7–96.5 °C; yield = 3.75(m, 1H), 3.76 (s, 3H), 3.58–3.51 (m, 1H), 2.88 (d, J = 3.3 Hz,
1
85.5%. H NMR (500 MHz, CDCl3, 25 °C): δ 7.50 (d, J = 7.4 Hz, 1H), 1.84 (dd, J = 7.1, 5.4 Hz, 1H) ppm; 13C{1H}NMR (126 MHz,
1H), 7.30–7.26 (m, 1H), 7.17 (t, J = 8.2 Hz, 1H), 7.01 (t, J = 7.4 CDCl3, 25 °C, mixture of diastereoisomers): Major δ 154.83
Hz, 1H), 6.88 (d, J = 8.2 Hz, 1H), 6.68–6.61 (m, 2H), 6.53 (dd, J = (CAr–O), 151.55 (CAr–O), 140.29 (CAr), 128.53 (CArH), 127.95
8.2, 1.9 Hz, 1H), 5.40 (t, J = 4.6 Hz, 1H), 4.68 (dd, J = 9.2, 4.1 Hz, (CArH), 126.22 (CArH), 118.39 (CArH), 114.76 (CArH), 83.50 (CH),
1H), 3.94 (dt, J = 11.4, 5.5 Hz, 1H), 3.89 (s, 3H), 3.78 (s, 3H), 74.00 (CH), 61.22 (CH2), 55.68 (OCH3); Minor δ 154.86 (CAr–O),
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152.05 (CAr–O), 139.76 (CAr), 128.60 (CArH), 128.29 (CArH), C17H20O5 304.1315, found 304.1311. IR: 3279, 2924, 2837,
126.94 (CArH), 118.18 (CArH), 114.82 (CArH), 84.62 (CH), 74.02 1507, 1233, 1174, 1112, 1040 cm-1.
(CH), 61.08 (CH2), 55.70 (OCH3) ppm. HRMS (FAB+) m/z: 1-(3,4-Dimethoxyphenyl)-2-phenoxypropane-1,3-diol (1q)6k
:
[M+H]+ calcd for C16H18O4 274.1205, found 274.1201. IR: 3432, The title compound 1q was synthesized according to general
2937, 2835, 1505, 1454, 1291, 1218, 1035 cm-1.
procedure A and obtained as a white solid. No attempt was
2-(4-Methoxyphenoxy)-1-(2-methoxyphenyl)propane-1,3-diol made to separate the diastereomer mixture. 1H NMR (500
(1n): The title compound 1n was synthesized according to MHz, CDCl3, 25 °C, mixture of diastereoisomers): δ 7.35–7.23
general procedure A. White solid; mp = 89.6°C; yield = 91.1%. (m, 2H), 7.02–6.81 (m, 6H); Major δ 5.03 (dd, J = 5.2, 3.4 Hz,
1H NMR (500 MHz, CDCl3, 25 °C): δ 7.48 (dd, J = 7.6, 1.3 Hz, 1H), 4.41 (dd, J = 9.8, 4.6 Hz, 1H), 3.95 (ddd, J = 11.1, 6.0, 4.9
1H), 7.29–7.22 (m, 1H), 6.98 (td, J = 7.5, 0.7 Hz, 1H), 6.95–6.90 Hz, 1H), 3.91–3.88 (m, 1H), 3.86 (s, 3H), 3.86 (s, 3H), 2.78 (d, J =
(m, 2H), 6.83 (d, J = 8.1 Hz, 1H), 6.81–6.76 (m, 2H), 5.33 (t, J = 3.4 Hz, 1H), 2.23 (t, J = 6.4 Hz, 1H); Minor δ 5.00 (dd, J = 6.7,
4.5 Hz, 1H), 4.51 (dt, J = 5.1, 4.0 Hz, 1H), 3.92–3.86 (m, 1H), 2.8 Hz, 1H), 4.41–4.39 (m, 1H), 3.88 (s, 3H), 3.87 (s, 3H), 3.85–
3.81 (s, 3H), 3.75 (s, 3H), 3.78–3.72 (m, 1H), 3.38 (d, J = 5.2 Hz, 3.79 (m, 1H), 3.64–3.55 (m, 1H), 2.83 (d, J = 3.0 Hz, 1H), 1.82
1H), 2.54 (t, J = 5.8 Hz, 1H) ppm; 13C{1H}NMR (126 MHz, CDCl3, (dd, J = 7.1, 5.6 Hz, 1H) ppm; 13C{1H}NMR (126 MHz, CDCl3, 25
25 °C): δ 156.04 (CAr–O), 154.42 (CAr–O), 151.85 (CAr–O), °C, mixture of diastereoisomers): Major δ 157.68 (CAr–O),
128.76 (CArH), 127.98 (CAr), 127.50 (CArH), 121.01 (CArH), 117.74 149.06 (CAr–O), 148.73 (CAr–O), 132.89 (CAr), 129.66 (CArH),
(CArH), 114.63 (CArH), 110.29 (CArH), 80.48 (CH), 70.19 (CH), 121.91 (CArH), 118.65 (CArH), 116.58 (CArH), 111.07 (CArH),
61.58 (CH2), 55.71 (OCH3), 55.31 (OCH3) ppm. HRMS (FAB+) 109.43 (CArH), 81.90 (CH), 73.99 (CH), 61.50 (CH2), 55.93
m/z: [M+H]+ calcd for C17H20O5 307.1311, found 304.1318. IR: (OCH3), 55.93 (OCH3) ppm; Minor δ 158.04 (CAr–O), 149.15
3461, 2933, 2846, 1507, 1224, 1067, 1038, 1029 cm-1.
(CAr–O), 149.01 (CAr–O), 132.13 (CAr), 129.77 (CArH), 122.06
2-(4-Methoxyphenoxy)-1-(3-methoxyphenyl)propane-1,3-diol (CArH), 119.38 (CArH), 116.49 (CArH), 111.07 (CArH), 109.89
(1o): The title compound 1o was synthesized according to (CArH), 83.07 (CH), 73.85 (CH), 61.18 (CH2), 55.93 (OCH3), 55.93
general procedure A. White solid; mp = 67.5–69.0°C; yield = (OCH3) ppm.
79.4%. No attempt was made to separate the diastereomer 1-(3,4-Dimethoxyphenyl)-2-(2-methoxyphenoxy)propane-1,3-
mixture. 1H NMR (500 MHz, CDCl3, 25 °C, mixture of diol (1r)15: The title compound 1r was synthesized according to
diastereoisomers): δ 7.30–7.24 (m, 1H), 7.05–6.94 (m, 2H), general procedure A and obtained as a white solid. 1H NMR
6.94–6.84 (m, 2H), 6.84–6.77 (m, 3H); Major δ 5.09–5.04 (m, (500 MHz, CDCl3, 25 °C): δ 7.06 (d, J = 8.2 Hz, 1H), 7.02–6.87
1H), 4.27 (dd, J = 9.0, 4.7 Hz, 1H), 3.95–3.88 (m, 1H), 3.85–3.81 (m, 5H), 6.84 (d, J = 8.3 Hz, 1H), 5.02–4.96 (m, 1H), 4.17 (ddd, J
(m, 1H), 3.80 (s, 3H), 3.76 (s, 3H), 2.85 (d, J = 3.5 Hz, 1H), 2.20 = 5.9, 4.7, 3.6 Hz, 1H), 3.95–3.90 (m, 1H), 3.90 (s, 3H), 3.88 (s,
(t, J = 6.4 Hz, 1H) ppm; Minor δ 5.00 (dd, J = 6.6, 3.3 Hz, 1H), 3H), 3.87 (s, 3H), 3.70–3.62 (m, 1H), 3.42 (d, J = 3.3 Hz, 1H),
4.27–4.24 (m, 1H), 3.81 (s, 3H), 3.80–3.77 (m, 1H), 3.76 (s, 3H), 2.67 (dd, J = 7.8, 5.4 Hz, 1H) ppm; 13C{1H}NMR (126 MHz,
3.57 (m, 1H), 2.88–2.86 (m, 1H), 1.83 (dd, J = 7.2, 5.4 Hz, 1H) CDCl3, 25 °C): δ 151.67 (CAr–O), 148.99 (CAr–O), 148.43 (CAr–O),
ppm; 13C{1H}NMR (126 MHz, CDCl3, 25 °C, mixture of 146.82 (CAr–O), 132.31 (CAr), 124.35 (CArH), 121.66 (CArH),
diastereoisomers): Major δ 159.81 (CAr–O), 154.84 (CAr–O), 121.21 (CArH), 118.34 (CArH), 112.12 (CArH), 110.94 (CArH),
151.52 (CAr–O), 141.93 (CAr), 129.58 (CArH), 118.49 (CArH), 109.05 (CArH), 87.60 (CH), 72.62 (CH), 60.72 (CH2), 55.90
118.37 (CArH), 114.78 (CArH), 113.33 (CArH), 111.83 (CArH), (OCH3), 55.90 (OCH3), 55.88 (OCH3) ppm.
83.38 (CH), 73.84 (CH), 61.20 (CH2), 55.69 (OCH3), 55.29 (OCH3) 2-(2,6-Dimethoxyphenoxy)-1-phenylpropane-1,3-diol
(1s):
ppm; Minor δ 159.83 (CAr–O), 154.85 (CAr–O), 152.04 (CAr–O), The title compound 1s was synthesized according to general
141.39 (CAr), 129.63 (CArH), 119.24 (CArH), 118.15 (CArH), 114.81 procedure A. Colorless sticky liquid; yield = 83.6%. 1H NMR
(CArH), 113.87 (CArH), 112.37 (CArH), 84.50 (CH), 73.96 (CH), (500 MHz, CDCl3, 25 °C): δ 7.39–7.30 (m, 4H), 7.27–7.22 (m,
61.13 (CH2), 55.70 (OCH3), 55.29 (OCH3) ppm. HRMS (FAB+) 1H), 7.08 (t, J = 8.4 Hz, 1H), 6.64 (d, J = 8.4 Hz, 2H), 5.09 (t, J =
m/z: [M+H]+ calcd for C17H20O5 304.1317, found 304.1315. IR: 3.4 Hz, 1H), 4.23–4.17 (m, 1H), 4.11 (d, J = 3.4 Hz, 1H), 3.94–
3463, 2952, 2837, 1583, 1507, 1282, 1236, 1222, 1069, 1039 3.89 (m, 1H), 3.88 (s, 6H), 3.47 (ddd, J = 12.0, 8.3, 2.7 Hz, 1H),
cm-1.
3.13 (dd, J = 8.3, 3.9 Hz, 1H); 13C{1H}NMR (126 MHz, CDCl3, 25
2-(4-Methoxyphenoxy)-1-(4-methoxyphenyl)propane-1,3-diol °C): δ 153.57 (CAr–O), 139.42 (CAr), 134.93 (CAr–O), 128.32
(1p): The title compound 1p was synthesized according to (CArH), 127.36 (CArH), 125.79 (CArH), 124.52 (CArH), 105.31
general procedure A. White solid; mp = 75.6–76.4°C; yield = (CArH), 86.96 (CH), 72.81 (CH), 60.52 (CH2), 56.16 (OCH3) ppm.
1
93.8%. H NMR (500 MHz, CDCl3, 25 °C): δ 7.33 (d, J = 8.6 Hz, HRMS (FAB+) m/z: [M+H]+ calcd for C17H21O5 304.1306, found
2H), 6.89 (d, J = 8.6 Hz, 2H), 6.84 (d, J = 9.1 Hz, 2H), 6.79 (d, J = 304.1311. IR: 3500, 2939, 2839, 1596, 1478, 1452, 1295, 1254,
9.1 Hz, 2H), 5.05–4.99 (m, 1H), 4.24 (dd, J = 9.4, 4.6 Hz, 1H), 1221, 1109, 1025 cm-1
3.91 (ddd, J = 11.2, 6.0, 5.0 Hz, 1H), 3.86–3.81 (m, 1H), 3.80 (s, 2-(2,6-Dimethoxyphenoxy)-1-(3,4-dimethoxyphenyl)propane-
3H), 3.75 (s, 3H), 2.71 (d, J = 3.4 Hz, 1H), 2.21 (t, J = 6.4 Hz, 1H) 1,3-diol (1t)19: The title compound 1t was synthesized
ppm; 13C{1H}NMR (126 MHz, CDCl3, 25 °C, mixture of according to general procedure A and obtained as a colorless
diastereoisomers): δ 159.30 (CAr–O), 154.77 (CAr–O), 151.65 sticky liquid. 1H NMR (500 MHz, CDCl3, 25 °C): δ 7.09 (t, J = 8.4
(CAr–O), 132.43 (CAr), 127.47 (CArH), 118.34 (CArH), 114.74 Hz, 1H), 6.96 (d, J = 1.2 Hz, 1H), 6.88–6.79 (m, 2H), 6.65 (d, J =
(CArH), 113.92 (CArH), 83.47 (CH), 73.76 (CH), 61.33 (CH2), 55.67 8.4 Hz, 2H), 5.03 (t, J = 3.4 Hz, 1H), 4.19–4.14 (m, 1H), 4.12 (d, J
(OCH3), 55.30 (OCH3) ppm. HRMS (FAB+) m/z: [M+H]+ calcd for = 3.3 Hz, 1H), 3.93–3.90 (m, 1H), 3.89 (s, 6H), 3.89 (s, 3H), 3.86
8 | J. Name., 2012, 00, 1-3
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(s, 3H), 3.49 (ddd, J = 12.0, 8.3, 2.8 Hz, 1H), 3.13 (dd, J = 8.3, organic layer was removed, and aqueous layer was extracted
3.9 Hz, 1H) ppm; 13C{1H}NMR (126 MHz, CDCl3, 25 °C): δ 153.56 with ethyl acetate. The combined organic layers were washed
(CAr–O), 149.00 (CAr–O), 148.22 (CAr–O), 134.99 (CAr), 132.04 with brine, dried over Na2SO4, filtered, and concentrated
(CArH), 124.49 (CArH), 118.12 (CArH), 111.03 (CArH), 109.02 under reduced pressure. The residue was purified by flash
(CArH), 105.31 (CArH), 87.04 (CH), 72.46 (CH), 60.61 (CH2), 56.16 chromatography on silica gel using a continuous gradient-
(OCH3), 56.16 (OCH3), 55.92 (OCH3) ppm.
elution
with
ethyl
acetate/hexanes
(1:4)
or
1-(4-Hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)prop- dichloromethane/methanol (95:5) to afford the corresponding
ane-1,3-diol (1u)15: The title compound 1u was synthesized phenol derivative and benzoic acid derivative, respectively.
according to general procedure A and obtained as a sticky Phenol (2a)20
:
The title compound 2a was synthesized
white solid. No attempt was made to separate the according to general procedure B using 1a 1b 1c 1d, or 1q as
,
,
,
diastereomer mixture. 1H NMR (500 MHz, CDCl3, 25 °C, lignin model compound. Pale yellow solid. H NMR (500 MHz,
mixture of diastereoisomers): δ 7.13–7.00 (m, 1H), 6.97–6.80 CDCl3, 25 °C): δ 7.27–7.22 (m, 2H), 6.96–6.91 (m, 1H), 6.85–
(m, 6H); Major δ 5.87 (s, 1H), 4.96–4.92 (m, 1H), 4.17–4.14 (m, 6.81 (m, 2H), 4.81 (s, 1H) ppm; 13C NMR (126 MHz, CDCl3, 25
1H), 3.94–3.88 (m, 1H), 3.84 (s, 3H), 3.83 (s, 3H), 3.74 (d, J = 3.2 °C): δ 155.53, 129.69, 120.87, 115.30 ppm.
1
Hz, 1H), 3.68–3.60 (m, 1H), 3.05–3.02 (m, 1H); Minor δ 5.91 (s, 2-Methoxyphenol (2b)21
1H), 4.96–4.92 (m, 1H), 4.03 (dt, J = 7.7, 3.7 Hz, 1H), 3.94–3.88 synthesized according to general procedure B using 1e
:
The title compound 2b was
1f 1g,
,
,
(m, 1H), 3.88 (s, 3H), 3.83 (s, 3H), 3.63–3.60 (m, 1H), 3.50–3.43 1h, or 1r as lignin model compound. Yellow liquid. 1H NMR
(m, 1H), 2.96–2.90 (m, 1H) ppm; 13C{1H}NMR (126 MHz, CDCl3, (500 MHz, CDCl3, 25 °C): δ 6.94–6.90 (m, 1H), 6.89–6.84 (m,
25 °C, mixture of diastereoisomers): Major δ 151.52 (CAr–O), 3H), 5.65–5.59 (m, 1H), 3.88 (s, 3H) ppm; 13C NMR (126 MHz,
146.90 (CAr–O), 146.65 (CAr–O), 145.11 (CAr–O), 131.90 (CAr), CDCl3, 25 °C): δ 146.59, 145.70, 121.48, 120.15, 114.54, 110.73,
124.13 (CArH), 121.63 (CArH), 120.81 (CArH), 119.06 (CArH), 55.88 ppm.
114.31 (CArH), 112.19 (CArH), 108.75 (CArH) 87.23 (CH), 72.77 3-Methoxyphenol (2c)21
(CH), 60.75 (CH2), 55.96 (OCH3), 55.88 (OCH3); Minor δ 151.25 synthesized according to general procedure B using 1i
:
The title compound 2c was
1j 1k
,
,
,
(CAr–O), 147.62 (CAr–O), 146.71 (CAr–O), 145.59 (CAr–O), 131.51 or 1l as lignin model compound. Yellow liquid. 1H NMR (500
(CAr), 124.20 (CArH), 121.70 (CArH), 120.93 (CArH), 120.25 (CArH), MHz, CDCl3, 25 °C): δ 7.12 (t, J = 8.3 Hz, 1H), 6.50 (ddd, J = 8.3,
114.38 (CArH), 112.19 (CArH), 109.47 (CArH) 89.38 (CH), 73.98 2.3, 0.9 Hz, 1H), 6.47–6.38 (m, 2H), 5.58 (s, 1H), 3.76 (s, 3H)
(CH), 61.04 (CH2), 55.90 (OCH3), 55.89 (OCH3) ppm.
ppm; 13C NMR (126 MHz, CDCl3, 25 °C): δ 160.82, 156.68,
1-(4-Hydroxy-3,5-dimethoxyphenyl)-2-(2-methoxyphenoxy)-
130.23, 107.97, 106.53, 101.61, 55.32 ppm.
propane-1,3-diol (1v)7b
:
The title compound 1v was 4-Methoxyphenol (2d)21
:
The title compound 2d was
synthesized according to general procedure A and obtained as synthesized according to general procedure B using 1m 1n 1o
white solid. No attempt was made to separate the or 1p as lignin model compound. Yellow solid. 1H NMR (500
,
,
,
a
diastereomer mixture. 1H NMR (500 MHz, CDCl3, 25 °C, MHz, CDCl3, 25 °C): δ 6.82–6.73 (m, 4H), 4.82 (s, 1H), 3.76 (s,
mixture of diastereoisomers): δ 7.15–7.03 (m, 1H), 6.99–6.88 3H) ppm; 13C NMR (126 MHz, CDCl3, 25 °C): δ 153.74, 149.47,
(m, 3H), 6.70–6.60 (m, 2H); Major δ 5.56 (s, 1H), 4.95 (dd, J = 116.08, 114.91, 55.84 ppm.
8.1, 5.5 Hz, 1H), 4.17–4.13 (m, 1H), 3.95–3.85 (m, 1H), 3.88 (s, 2,6-Dimethoxyphenol (2e)20: The title compound 2e was
3H), 3.86 (s, 6H), 3.66 (ddd, J = 12.5, 8.0, 4.0 Hz, 1H), 3.60 (d, J synthesized according to general procedure B using 1s or 1t as
= 3.2 Hz, 1H), 2.85–2.78 (m, 1H); Minor δ 5.60 (s, 1H), 4.95 (m, lignin model compound. Yellow liquid. 1H NMR (500 MHz,
1H), 4.01 (dd, J = 7.6, 3.8 Hz, 1H), 3.91 (s, 3H), 3.88 (s, 6H), 3.73 CDCl3, 25 °C): δ 6.80 (t, J = 8.3 Hz, 1H), 6.58 (d, J = 8.3 Hz, 2H),
(d, J = 1.7 Hz, 1H), 3.68–3.63 (m, 1H), 3.49 (ddd, J = 12.3, 8.5, 5.52 (s, 1H), 3.89 (s, 6H) ppm; 13C NMR (126 MHz, CDCl3, 25
3.7 Hz, 1H), 2.85–2.78 (m, 1H) ppm ; 13C{1H}NMR (126 MHz, °C): δ 147.28, 134.89, 119.08, 104.93, 56.28 ppm.
CDCl3, 25 °C, mixture of diastereoisomers): Major δ 151.72 Benzoic acid (3a)22: The title compound 3a was synthesized
(CAr–O), 147.11 (CAr–O), 134.15 (CAr–O), 130.89 (CAr–O), 124.39 according to general procedure B using 1a, 1e, 1i, 1m, or 1s as
(CAr), 121.70 (CArH), 121.22 (CArH), 112.20 (CArH), 102.74 (CArH), lignin model compound. Yellow solid. 1H NMR (500 MHz,
87.61 (CH), 72.90 (CH2), 60.77 (CH2), 56.37 (OCH3), 55.92 CDCl3, 25 °C): δ 12.82 (s, 1H), 8.13 (dd, J = 8.3, 1.3 Hz, 2H),
(OCH3); Minor δ 151.41 (CAr–O), 146.87 (CAr–O), 134.60 (CAr–O), 7.68–7.56 (m, 1H), 7.48 (t, J = 7.8 Hz, 2H) ppm; 13C NMR (126
130.62 (CAr–O), 124.42 (CAr), 121.76 (CArH), 121.22 (CArH), MHz, CDCl3, 25 °C): δ 172.48, 133.85, 130.25, 129.34, 128.51
112.21 (CArH), 103.78 (CArH), 89.67 (CH), 74.28 (CH2), 61.05 ppm.
(CH2), 56.37 (OCH3), 55.94 (OCH3) ppm.
General procedure for the cleavage reaction of the dilignol synthesized according to general procedure B using 1b
model compound (1a
B): The lignin model compound (0.5 or 1n as lignin model compound. Yellow solid. 1H NMR (500
2-Methoxybenzoic acid (3b)22: The title compound 3b was
1f 1j
,
,
,
,
mmol) and sodium tert-butoxide (2 mmol) was placed into a MHz, CDCl3, 25 °C): δ 10.73 (s, 1H), 8.20 (dd, J = 7.8, 1.8 Hz,
10 mL two-necked round-bottom flask, equipped with a 1H), 7.58 (ddd, J = 8.4, 7.4, 1.8 Hz, 1H), 7.15 (td, J = 7.8, 0.9 Hz,
magnetic stirring bar and rubber septa, under an argon 1H), 7.07 (d, J = 8.4 Hz, 1H), 4.09 (s, 3H) ppm; 13C NMR (126
atmosphere. The flask was evacuated via a vacuum and refilled MHz, CDCl3, 25 °C): δ 165.26, 158.02, 135.09, 133.91, 122.31,
with oxygen three times. The mixture was then stirred and 117.64, 111.62, 56.69 ppm.
heated at 30 °C for 16 h. The resulting mixture was quenched 3-Methoxybenzoic acid (3c)23: The title compound 3c was
with the addition of water and diluted with ethyl acetate. The synthesized according to general procedure B using 1c, 1g, 1k,
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or 1o as lignin model compound. Yellow solid. 1H NMR (500 lignin model compound was carried via the aforementioned
MHz, CDCl3, 25 °C): δ 12.32 (s, 1H), 7.73 (d, J = 7.7 Hz, 1H), 7.63 procedure for the cleavage reaction of dilignol model
(s, J = 2.2 Hz, 1H), 7.39 (t, J = 7.9 Hz, 1H), 7.17 (dd, J = 8.2, 2.2 compounds, with only a slight modification. The modified part
Hz, 1H), 3.87 (s, 3H) ppm; 13C NMR (126 MHz, CDCl3, 25 °C): δ is as follows: the residue was purified by flash chromatography
172.02, 159.63, 130.06, 129.55, 122.71, 120.51, 114.41, 55.48 on silica gel eluted with ethyl acetate/hexanes (from 1:5 to
ppm.
4-Methoxybenzoic acid (3d)22: The title compound 3d was 4-Hydroxy-3-methoxybenzaldehyde
synthesized according to general procedure B using 1d 1h 1l compound 22 was synthesized according to general procedure
2:1).
(22)25
:
The
title
,
,
,
or 1p as lignin model compound. Pale yellow solid. 1H NMR C using 21 as lignin model compound. Pale yellow solid. 1H
(500 MHz, CDCl3, 25 °C): δ 12.11 (s, 1H), 8.07 (d, J = 8.9 Hz, 2H), NMR (500 MHz, CDCl3, 25 °C): δ 9.83 (s, 1H), 7.45–7.41 (m, 2H),
6.95 (d, J = 8.9 Hz, 2H), 3.88 (s, 3H) ppm; 13C NMR (126 MHz, 7.06–7.03 (m, 1H), 6.24 (s, 1H), 3.97 (s, 3H) ppm; 13C NMR (126
CDCl3, 25 °C): δ 171.47, 164.07, 132.38, 121.62, 113.77, 55.50 MHz, CDCl3, 25 °C): δ 190.93, 151.72, 147.18, 129.90, 127.55,
ppm.
3,4-Dimethoxybenzoic acid (3e)22: The title compound 3e was 4-Hydroxy-3-methoxycinnamaldehyde (23)26
synthesized according to general procedure B using 1q 1r, or compound 23 was synthesized according to general procedure
114.41, 108.80, 56.14 ppm.
:
The title
,
1
1
1t as lignin model compound. Yellow solid. H NMR (500 MHz, C using 21 as lignin model compound. Yellow liquid. H NMR
CDCl3, 25 °C): δ 13.20–11.38 (s, 1H), 7.79 (dd, J = 8.4, 1.9 Hz, (500 MHz, CDCl3, 25 °C): δ 9.65 (d, J = 7.7 Hz, 1H), 7.40 (d, J =
1H), 7.61 (d, J = 1.9 Hz, 1H), 6.93 (d, J = 8.4 Hz, 1H), 3.96 (s, 15.8 Hz, 1H), 7.12 (dd, J = 8.2, 1.8 Hz, 1H), 7.07 (d, J = 1.8 Hz,
3H), 3.95 (s, 3H) ppm; 13C NMR (126 MHz, CDCl3, 25 °C): δ 1H), 6.96 (d, J = 8.2 Hz, 1H), 6.60 (dd, J = 15.8, 7.7 Hz, 1H), 6.15
172.14, 153.77, 148.70, 124.63, 121.74, 112.33, 110.35, 56.08, (br, 1H), 3.94 (s, 3H) ppm; 13C NMR (126 MHz, CDCl3, 25 °C): δ
56.02 ppm.
193.58, 153.02, 148.91, 146.93, 126.70, 126.49, 124.07, 114.92,
4-Hydroxy-3-methoxybenzoic acid (3f)24: The title compound 109.42, 56.02 ppm.
3f was synthesized according to general procedure B using 1u
as lignin model compound. Yellow solid. 1H NMR (500 MHz,
Conflicts of interest
acetone-d6, 25 °C): δ 8.3 (br, 1H), 7.66 (dd, J = 8.2, 1.9 Hz, 1H),
7.64 (d, J = 1.9 Hz, 1H), 6.99 (d, J = 8.2 Hz, 1H), 4.00 (s, 3H) ppm;
13C NMR (126 MHz, acetone-d6, 25 °C): δ 166.26, 150.48,
146.64, 123.71, 121.39, 114.10, 112.18, 55.42 ppm.
There are no conflicts to declare.
4-Hydroxy-3,5-dimethoxybenzoic acid (3g)24
: The title compound
Acknowledgements
3g was synthesized according to general procedure B using 1v
as lignin model compound. Yellow solid. 1H NMR (500 MHz,
CDCl3, 25 °C): δ 11.17–10.75 (br, 1H), 7.39 (s, 2H), 5.98 (br, 1H),
3.97 (s, 6H) ppm; 13C NMR (126 MHz, CDCl3, 25 °C): δ 170.81,
146.71, 140.03, 119.97, 107.28, 56.47 ppm.
We gratefully acknowledge the NRF grant (No.
2016R1A2B4010181) and NRF Basic Research Laboratory
Program (2016R1A4A1011451) for financial support of this
work.
Synthesis
of
2-(4-(1,3-dihydroxy-2-(4-methoxyphenoxy)
pro-
propyl)-2-methoxyphenoxy)-1-(3,4-dimethoxyphenyl)
Notes and references
pane-1,3-diol as trimeric lignin model compound (21): The
title compound was prepared according to the previously
reported procedures.12b White sticky semi-solid; mp = 53.5–55
°C; yield = 86.7%. No attempt was made to separate the
diastereomer mixture. 1H NMR (500 MHz, CDCl3, 25 °C,
mixture of diastereoisomers): δ 7.16–6.72 (m, 10H), 5.05–4.93
(m, 2H), 4.27–4.10 (m, 2H), 3.98–3.53 (m, 16H), 3.50–3.35(m,
1H), 2.96–2.83 (m, 1H), 2.74–2.60 (m, 1H), 2.25–1.85 (m, 1H)
ppm; 13C{1H}NMR (126 MHz, CDCl3, 25 °C, mixture of
diastereoisomers): δ 154.92 (CAr–O), 154.85 (CAr–O), 151.58
(CAr–O), 149.07 (CAr–O), 148.55 (CAr–O), 146.46 (CAr–O), 136.63
(CAr), 132.34 (CAr), 120.77 (CArH), 119.45 (CArH), 118.41 (CArH),
118.25 (CArH), 118.09 (CArH), 114.84 (CArH), 114.74 (CArH),
111.06 (CArH), 110.30 (CArH), 109.23 (CArH), 84.39 (CH), 83.40
(CH), 73.69 (CH), 72.77 (CH), 61.48 (CH2), 60.82 (CH2), 56.02
(OCH3), 55.94 (OCH3), 55.94 (OCH3), 55.66 (OCH3) ppm. HRMS
(FAB+) m/z: [M+H]+ calcd for C28H34O10 530.2152, found
530.2149. IR: 3459, 2937, 2833, 1592, 1505, 1463, 1419, 1262,
1225, 1138, 1028 cm-1
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