Angewandte
Chemie
Table 3: Catalytic olefination of alcohols with aryl alkyl sulfones using
complex 4.[a]
Table 4: Direct conversion of alcohol hydroxy groups into methyl
groups.[a]
Entry
R
Product
Yield[b] [%]
Entry
R
R’
Product
Yield[b] [%]
1
2
3
4
p-MeOC6H4
3,4-(MeO)2C6H3
p-PhC6H4
11a
11b
11c
11d
61
75
72
71
1
2
3
4
5
6
7
8
p-MeOC6H4
p-ClC6H4
p-MeC6H4
p-PhC6H4
1-naphthyl
p-MeOC6H4
p-MeC6H4
2-naphthyl
Ph
Ph
Ph
Ph
Ph
Me
Me
Me
Ph
Ph
Ph
10a
10b
10c
10d
10e
10 f
10g
10h
10i
71
70
72
69
76
71
50
52
55
61
35
2-naphthyl
[a] Reaction conditions: alcohol (1 mmol), dimethyl sulfone
(1.06 mmol), KOtBu (1.16 mmol), and pre-catalyst 4 (2.5 mol%) were
heated at 1258C at 2.5 bar H2 pressure in THF (2 mL) for 20 hours.
[b] Yield of isolated product.
À
=
9
10
11
(E)-Ph CH CH
6-methylpyridyl
benzyl
10j
10k
thylmethanol gave the corresponding alkanes in good yields
(71–75%; entries 2–4). This reaction sequence with only one
catalyst enables the unprecedented direct conversion of
a hydroxy group into a methyl group. The reaction of 3,4-
dimethoxybenzyl alcohol with deuterated dimethyl sulfone,
which resulted in deuterium incorporation at the terminal
carbon atom of the desired styrene, provided direct evidence
that the methylene group originates from dimethyl sulfone
(Scheme 3).
[a] Reaction conditions: alcohol (1 mmol), sulfone (1.06 mmol), KOtBu
(1.16 mmol), and pre-catalyst 4 (0.025 mmol) were heated at reflux in
dioxane (2 mL) in an open system under argon for 5 hours at 1258C (oil-
bath temperature). [b] Yield of isolated product.
reaction conditions gave the corresponding E-stilbenes in
good yields (69–76%; Table 3, entries 1–5). Similarly, the
reaction of ethyl phenyl sulfone with 4-methoxybenzyl
alcohol and 4-methylbenzyl alcohol gave 10 f and 10g in
good yields (entries 6–8). Under similar reaction conditions,
cinnamyl alcohol also reacted with benzyl phenyl sulfone to
give 10i, which was isolated in 55% yield. Heterocyclic
alcohols, such as 6-methyl-2-pyridinemethanol, reacted with
benzyl phenyl sulfone under similar reaction conditions,
giving 2-methyl-6-styrylpyridine (10j) in 61% yield with an
E/Z ratio of 3:1 (entry 10). The reaction of 2-phenylethanol
with benzyl phenyl sulfone gave the desired product 10k in
35% yield.
Scheme 3. Deuterium-labelling experiments confirm that the carbon
source is dimethyl sulfone.
During the reaction of differently substituted benzyl
alcohols with benzyl phenyl sulfone, potassium benzenesul-
fonate was also isolated as an insoluble salt, which precipi-
tated from the organic solvent.
Significantly, although hydrogen gas was liberated in these
reactions, no (or only a trace amount of) hydrogenation to
form the corresponding alkanes was observed when the
reactions were performed in an open system under reflux. The
iridium-catalyzed Wittig olefination with transfer hydrogena-
tion was reported to convert alcohols into alkanes.[16] Encour-
aged by our results on the Julia olefination, we explored the
possibility of obtaining the hydrogenated product by perform-
ing the reaction in a sealed vessel. Thus the reaction of 4-
methoxybenzyl alcohol and dimethyl sulfone was performed
in a closed vessel, which resulted in a mixture of both alkane
and alkene (20:80). However, performing the reaction under
2.5 bar H2 pressure gave exclusively the alkane, with no olefin
being observed. Thus, when a THF solution containing 4-
methoxybenzyl alcohol, dimethyl sulfone, KOtBu, and pre-
catalyst 4 was heated in a Fischer–Porter tube under 2.5 bar
hydrogen pressure for 20 hours, GC–MS analysis showed the
formation of 1-ethyl-4-methoxybenzene. A small amount of
1-isopropyl-4-methoxybenzene was detected as well, and no
4-methoxystyrene was detected. The crude product was
purified by flash column chromatography to give 1-ethyl-4-
methoxybenzene (11a) in 61% yield (Table 4). Similarly, 3,4-
dimethoxybenzyl alcohol, 4-biphenylmethanol, and 2-naph-
To gain insight about possible intermediates during the
reaction course, complex 4 was treated with 1.1 equivalents of
KOtBu in THF and was then added to a THF solution
containing 10 equivalents of dimethyl sulfone and KOtBu,
and the mixture was stirred at room temperature for two
hours. Single crystals that were suitable for X-ray diffraction
were grown by layering the THF solution with n-pentane. The
crystal structure shows a polymeric complex, in which each
asymmetric unit contains one ruthenium pincer unit, two
À
C H-activated dimethyl sulfone ligands, three potassium
ions, and five THF molecules (see the Supporting Informa-
tion).[17] For clarity, we show only one unit (Figure 2). The
crystal structure shows the coordination of dimethyl sulfone
to ruthenium through the C25 carbon atom, the Ru1–C25
distance being 2.209 (4) ꢀ. One of the potassium cations is
connected to the oxygen atom (O1) of a carbonyl group and
to one of the oxygen atoms (O3) of the coordinated dimethyl
sulfone. Each potassium ion is also connected to another
dimethyl sulfone unit in the polymeric structure, shown as
a dotted line. The C10–C11 bond length is 1.378(8) ꢀ, and
there is only one hydrogen atom (H11) in the arm (C11),
1
revealing that the complex is dearomatized. In the H NMR
Angew. Chem. Int. Ed. 2014, 53, 1 – 5
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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