A new synthetic route to substituted quinones by radical-mediated coupling of organotellurium compounds with quinones

Article abstract of DOI:10.1016/S0040-4020(02)00784-6

Carbon-centered radicals generated from the corresponding organotellurium compounds react with a variety of quinones under photo-thermal conditions to give the monoaddition product in moderate to excellent yield. The reaction can be used for the synthesis of polyprenyl quinoid natural products and C-glycosides.

Full text of DOI:10.1016/S0040-4020(02)00784-6

Tetrahedron 58 (2002) 6805–6813
A new synthetic route to substituted quinones by radical-mediated
coupling of organotellurium compounds with quinones
*
Shigeru Yamago, Masahiro Hashidume and Jun-ichi Yoshida
*
Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 606-8501, Japan
Received 6 June 2002; accepted 2 July 2002
Abstract—Carbon-centered radicals generated from the corresponding organotellurium compounds react with a variety of quinones under
photo-thermal conditions to give the monoaddition product in moderate to excellent yield. The reaction can be used for the synthesis of
polyprenyl quinoid natural products and C-glycosides. q 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction
under thermolysis and photolysis,7 and the resulting
carbon-centered radicals could be used for various synthetic
reactions.8,9 Therefore, we envisaged that the radicals thus
generated would also be useful for the functionalization of
quinones. We report herein a new synthesis of substituted
quinones by the radical-mediated reaction of organo-
tellurium compounds with various quinones. Preliminary
results have already been reported.10 We now report the full
details of the study to demonstrate the synthetic scope of our
approach.
A great deal of attention has been focused on the synthesis
of substituted quinones because of their unique and diverse
biological function as mediators for electron-transfer
processes and antiviral and anticancer agents.1 Due to the
variety of available quinones, the attachment of the carbon
chain to the preexistent quinone skeleton is one of the most
attractive and straightforward synthetic approaches.2
Indeed, enormous effort has been devoted to the realization
of this process by organometallic-mediated reactions and
cycloadditions.3 However, while radical-mediated synthesis
would seem to be a desirable alternative,4 only a few
examples have been reported so far,5 and with limited
synthetic scope. This is probably because the most
conventional reaction system using alkyl halides and tin
hydride for carbon-centered radical generations could not be
applied owing to the high reactivity of the tin hydride
toward quinones.6 Among the radical-mediated syntheses,
the use of the Barton esters 1 as radical precursors under UV
irradiation seems to be the best method to date in terms of
high coupling efficiency, high functional group compat-
ibility, and availability of the radical precursors (Scheme
1).5d This method, however, still has drawbacks; the
reaction usually gives a mixture of two quinone products,
e.g. 3 and 4 from an initially formed group-transfer adduct,
2, with moderate selectivity, and the substitution of quinone
acceptors has been limited to mono and 1,2-di-substitution.
Therefore, the development of a new system that would
allow us to expand the synthetic efficiency of the radical-
mediated route to substituted quinones is strongly needed.
Scheme 1.
2. Results and discussions
2.1. Reaction with benzyl, allyl and alkyl tellurides
The reaction conditions have been examined in detail using
benzyl p-methylphenyl telluride (5a)11 and 1,4-benzo-
quinone (6A). Thus, 5a was heated with 6A (2.0 equiv.) in
C6H6 at 1008C under irradiation with a 200 W high pressure
Hg lamp in a Pyrex tube. After silica gel chromatography,
we isolated 2-benzyl-1,4-benzoquinone (7aA) in 57%
We have already reported that carbon-centered radicals are
reversibly generated from organotellurium compounds
Keywords: quinones; organotellurium compounds; radical precursors.
*
Corresponding authors. Tel.: þ81-75-753-5661; fax: þ81-75-753-5911;
e-mail: yamago@sbchem.kyoto-u.ac.jp, yoshida@sbchem.kyoto-u.ac.jp.
0040–4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(02)00784-6

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S. Yamago et al. / Tetrahedron 58 (2002) 6805–6813
benzoquinone (entry 14). Despite the side product
formation, this method allows direct introduction of
quinone groups onto carbohydrate molecules.
ð1Þ
The regioselectivity of the reaction deserves comment. The
reaction of the phenyl-substituted quinone 6D occurred at
the C-3 position, which is conjugated with the phenyl group,
to give the 2,3-disubstituted quinone 7aD (entry 4). In the
reaction of the t-butyl-substituted quinone 6E, the selectiv-
ity was controlled by steric factors, and the reaction afforded
a 7:3 mixture of the 2,6- and 2,5-disubstituted quinones in a
good combined yield (entry 5). In the reaction of prenyl
tolyl telluride (5b), the prenyl moiety selectively coupled
with quinones at the less hindered a-position, and the
corresponding g-coupling products could not be detected
(entries 8 and 9).
Table 1. Benzyl radical addition to 1,4-benzoquinones
Entry
Solvent
Conditions
Yield (%)
1
C6H6
C6H6
C6H6
C6H6
EtCN
EtOH
hn,a 1008C, 1 h
hn,a 1008C, 1 h
1008C, 1 h (dark)
1008C, 7 h (dark)
hn,a 1008C, 1 h
hn,a 1008C, 1 h
57
61
9
58
57
50
2b
3
4b
5
6
a
High pressure mercury lamp (200 W) was used.
3 equiv. of 6A was used.
b
In the reaction with 1,4-naphthoquinone (12), the reaction
mainly afforded 6-benzyl-1,4-naphthoquinone (13) as the
major product as expected in 52% yield (Scheme 2).
Analysis of the side products also revealed the formation of
14 in 22% yield together with the 5,6-dibenzyl adduct 15 in
11% yield. The formation of a 1,4-diketone adduct such as
14 was observed only in this reaction. Since triethylamine-
catalyzed aromatization of 14 to the corresponding
hydroquinone proceeded completely under mild thermal
conditions, 14 must be formed kinetically. While the origin
of the formation of 14 is unclear, it could be transformed
into 13 by base-catalyzed isomerization followed by air
oxidation of the resulting hydroquinone during work up.
Alternatively, quinone 12 could also be used as the
oxidizing agent of the hydroquinone.
yield (Table 1, entry 1). The tellurium moiety was not
incorporated into the product and was recovered
quantitatively as di-p-methylphenyl ditellulide. We also
isolated quinhydrone in about 40% yield. The reaction
in the dark was slow, but eventually gave the same
product after heating at 1008C (entries 3 and 4). The
effect of the solvent is marginal, and the reaction in
polar solvents, such as acetonitrile and ethanol,
produced virtually identical results (entries 5 and 6).
The lack of sensitivity to solvent is consistent with the
involvement of neutral radical species rather than polar
intermediates, such as radical ion species.
The synthetic scope of the current reaction was
examined, and the results are summarized in Table 2.
A variety of substituted quinones react with organotel-
lurium compounds to give the monoaddition product in
good to excellent yield. It is worth noting that tri-
substituted quinones, e.g. 2,3-dimethoxy-5-methyl-1,4-
benzoquinone (6C), 2-methyl-1,4-naphthoquinone (8)
and 2-hydroxy-1,4-naphthoquinone, could be used as
substrates, and that the reaction afforded tetra-substi-
tuted quinones in good to excellent yields (entries 3, 6–
9 and 11). Since the reaction proceeded under neutral
conditions, free hydroxyl groups were compatible with
the reaction conditions (entry 7).
The current method can be applied to the synthesis of
polyprenyl quinonoids as shown in Scheme 3. Thus, geranyl
tolyl telluride 16 (a 73:23 mixture of the trans and cis
isomers), which was prepared by SmI2-mediated coupling
of geranyl bromide and ditolyl ditelluride,12 was allowed to
react with 6C and 8 to give ubiquinone 2 (17) and Vitamin
We also used a variety of organotellurium compounds
as radical precursors, e.g. benzyl, prenyl isopropyl, a-
amino and glycosyl radicals generated from 5, 9 and 10,
respectively. The reaction of prenyl derivative 5b with
6C afforded ubiquinone 1 in good yield (entry 8). In the
reaction of the glycosyl telluride 10, we detected a
considerable amount of the side product 11 (45% yield),
which could have resulted from the oxidative glycosyla-
tion of 10 with 1,4-hydroquinone mediated by 1,4-
Scheme 2. Et3N (0.1 equiv.), C6D6, 508C, 2 h, then air (87%) or Et3N
(0.1 equiv.), 12 (3 equiv.), C6H6, rt to 608C, 4 h (82%).

S. Yamago et al. / Tetrahedron 58 (2002) 6805–6813
Table 2. Radical-mediated synthesis of substituted quinones
6807
Entry
RTeAr
Quinone
Time (h)
Product
Yield (%)
1
2
3
4
5a
6A
6B
6C
6D
1
1
2
2.5
7aA
7aB
7aC
7aD
58
71
53
57
5
6E
1
55
23
87
6
1
7
8
1.5
2
64
41
5b
5c
6C
7bC
7cA
9
8
2
3
61
44
10
6A
11
12
14
8
6
1.5
2
50
44
39
9
6A
6A
10
The reaction was carried out with 2 equiv. of quinone under UV irradiation (200 W high pressure Hg lamp) at 1008C.
K2(10) (18), respectively, in moderate yields. Analysis of the
stereochemistry revealed that a 7:3 mixture of the trans and
cis isomers was formed in both cases. Because neryl tolyl
telluride, which was prepared from neryl chloride, isomer-
ized to 16 (ca. 7:3 mixture) before the coupling reaction
with the quinones took place, the observed stereoselectivity
would be reflected in the stability of the geranyl and neryl
radical intermediates.
Scheme 4. As the radical-mediated carbotelluration of
alkynes and alkenes is well known,8a,e,f,9c–f the initial step
of the current reaction would also follow the same pathway
to give 20. Elimination of aryltellurol from 20 would result
in the formation of 21. The aryltellurols thus formed reduce
the quinone 19 to the hydroquinone 22 with the generation
of the corresponding diaryl ditelluride.13 The key inter-
mediate 20, however, could not be detected by 1H NMR in
the experiments performed in C6D6 with various quinones.
2.2. Reaction mechanism
To clarify the involvement of 20, we carried out the reaction
with tetra-substituted quinones, where elimination of aryl
A plausible mechanism for the formation of 7 is shown in

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S. Yamago et al. / Tetrahedron 58 (2002) 6805–6813
Scheme 3. (a) SmI2, HMPA/THF, rt, 2 h, 41% (73% trans), (b) hn (200 W
Hg lamp), C6D6, 1008C, 1 h.
tellurol from the initial intermediate such as 20 was avoided.
The reaction of 5a with duroquinone (22) took place slowly
and afforded a mixture of several coupling products.
Although we could not observe the initial carbotellulated
Scheme 4.
1
adduct by isolation or by H NMR of the crude mixture in
the experiments carried out in C6D6, we were able to isolate
23, 24 and 25 in 38, 18, and 17% yields, respectively (Eq.
(2)). Formation of these compounds could be explained by
considering the intermediacy of the carbotellulated product
26 (Scheme 5). Thus, 26 reversibly generates radical 27
under the reaction conditions by carbon–tellurium bond
homolysis.6 The radical 27 undergoes a radical coupling
reaction with the benzyl radical generated from 5a to give
23. It also undergoes hydrogen atom abstraction from 22 to
give 24 and the conjugated radical 28, which couples with
the benzyl radical to give 25. These results are consistent
with the mechanism depicted in Scheme 4.
Scheme 5.
ð3Þ
ð2Þ
3. Conclusion
We have demonstrated that a variety of organotellurium
compounds undergo radical-mediated addition to the
carbon–carbon double bond of quinones to give the
monoaddition product in moderate to excellent yield. The
reaction allows the synthesis of biologically interesting
molecules, such as polyprenyl quinonoids and sugar-
quinone hybrid molecules. The reaction of acyl tellurides,
on the other hand, selectively takes place at the carbonyl
oxygen to give the bis-acylated hydroquinones in good
yields. We believe that these results clearly demonstrate the
advantage of the radical-mediated synthesis of quinones
using organotellurium compounds as radical precursors.
2.3. Reaction with acyl tellurides
We also examined the introduction of acyl groups onto
quinones via acyl radicals.14 Thus, benzoyl tolyl telluride
29i was heated with 1,4-benzoquinone (6A) in EtCN at
1008C under UV irradiation. Surprisingly, the reaction took
place at the oxygen moiety of the quinones, and the bis-
acylated hydroquinone 30i was isolated as the sole product
(Eq. (3)).15 When 2 equiv. of 29i was used, the yield was
improved to 78%. The p-chlorobenzoyl telluride 29ii also
afforded 30ii as the only product. The reaction could be
useful for the protection of quinones under neutral
conditions, and the product 30 could also serve as the
starting material for the photo-Fry rearrangement for the
introduction of acyl groups onto hydroquinones.16
4. Experimental
4.1. General remarks
1H and 13C NMR spectra were measured for a CDCl3

S. Yamago et al. / Tetrahedron 58 (2002) 6805–6813
6809
solution of the sample on Varian Gemini 200 or JEOL alpha
400 instruments (300/400 MHz for 1H and 75/100 MHz for
13C). The chemical shifts are reported in parts per million
(d). Infrared spectra were recorded on a Shimazu DR-8000;
absorptions are reported in cm21. Mass spectra were
recorded on JEOL IMS-300 or JEOL HX-110A spec-
trometers. 3-Nitrobenzyl alcohol was used as a matrix for
FAB-MS unless otherwise noted. Photochemical reactions
were carried out with USHIO Optical Modulex equipped
with a 200 W high pressure Hg lamp. Recycling preparative
HPLC was performed on a Japan Analytical Industry LC-
908 machine equipped with GPC column (JAIGEL 1H and
2H) using CHCl3 as eluent.
LRMS (EI) m/e 198 (M)þ; HRMS (EI) Calcd for C13H10O2
(M)þ, 198.0681; Found 198.0686.
4.2.3. 3-Benzyl-2,6-dichloro-1,4-benzoquione (7aB). IR
(KBr) 1684 (s), 1659 (s), 1291 (m), 1213 (m), 1105 (m),
1
1007 (m), 893 (m), 780 (s), 768 (m), 718 (s), 696 (m); H
NMR (300 MHz, CDCl3) 4.00 (s, 2H), 7.01 (s, 1H), 7.17–
7.31 (m, 5H); 13C NMR (75 MHz, CDCl3) 33.35 (CH2),
127.11 (CH), 128.76 (CH, 2C), 129.14 (CH, 2C), 133.62
(CH), 135.90 (C), 140.59 (C), 143.20 (C), 144.51 (C),
172.97 (C), 182.36 (C); LRMS (EI) m/e 268, 266 (M)þ;
HRMS (EI) Calcd for C13H8O2Cl2 (M)þ, 266.0094; Found
265.9901; Anal. Calcd for C13H0O2Cl2: C, 58.46; H, 3.02.
Found: C, 58.59; H, 2.88.
4.2. Materials
4.2.4. 2-Benzyl-5,6-dimethoxy-3-methyl-1,4-benzoqui-
none (7aC). IR (KBr) 1671 (s), 1642 (s), 1609 (s), 1267
(s), 1206 (m), 1156 (m); H NMR (300 MHz, CDCl3) 2.08
(s, 3H), 3.84 (s, 2H), 3.98 (s, 3H), 3.99 (s, 3H), 7.14–7.22
(m, 3H), 7.23–7.30 (m, 2H); 13C NMR (75 MHz, CDCl3)
12.45 (CH3), 31.70 (CH2), 61.21 (CH3, 2C), 126.60 (CH),
128.74 (CH), 128.79 (CH), 138.00 (C), 138.03 (C), 140.07
(C), 141.11 (C), 144.53 (C), 184.31 (CvO), 184.87 (CvO);
LRMS (EI) m/e 272 (M)þ; HRMS (EI) Calcd for C16H16O4
(M)þ, 272.1049; Found 272.1046.
Unless otherwise noted, materials obtained from commer-
cial suppliers were used without purification. Benzene was
distilled over CaH2, and was stored over molecular sieves.
EtCN was distilled successively from P2O5 and K2CO3 and
stored over molecular sieves. Organotellurium compounds
were prepared according to the procedure previously
reported.8f,17
1
4.2.1. p-Methylphenyl prenyl telluride (5b). Sodium
borohydride (2.65 g, 70.0 mmol) was added to a solution of
p-methylphenyl ditelluride (10.9 g, 25.0 mmol) and prenyl
chloride (5.23 g, 50.0 mmol) in ethanol (200 mL) in several
portions. After the mixture was stirred at room temperature for
2 h, polar materials were removed by passing the crude
mixture through a short pad of alumina oxide (50.0 g; elution
with degassed diethyl ether) under an argon atmosphere.
Removal of solvents followed by distillation under reduced
pressure (858C/0.8 mm Hg) gave 5b as an orange oil in 22%
yield (3.23 g, 11.2 mmol). This compound is sensitive to
oxygen, and was stored under an argon atmosphere. Due to its
instability, full spectroscopic characterization could not be
accomplished. 1H NMR (300 MHz, CDCl3) 1.39 (d,
J¼0.3 Hz, 3H), 1.68 (s, 3H), 2.35 (s, 3H), 3.61 (s, 3H) 5.42
(triplet of septet, J¼8.7, 1.3 Hz, 1H), 7.02 (d, J¼7.5 Hz, 2H),
7.65 (d, J¼8.1 Hz, 2H); 13C NMR (75 MHz, CDCl3) 6.71
(CH3), 16.99 (CH3), 21.23 (CH3), 25.52 (CH2), 108.28 (C),
122.12(CH), 129.89(CH, 2C), 134.01(C), 137.96(C), 140.13
(CH, 2C).
4.2.5. 2-Benzyl-3-phenyl-1,4-benzoquinone (7aD). IR
(KBr) 1653 (s), 1606 (m), 1588 (m), 1495 (m), 1453 (m);
1H NMR (400 MHz, CDCl3) 3.78 (s, 2H), 6.82 (d,
J¼10.1 Hz, 1H), 6.83 (d, J¼10.1 Hz, 1H), 6.91–6.95 (m,
2H), 7.10–7.21 (m, 5H), 7.40–7.46 (m, 2H); 13C NMR
(100 MHz, CDCl3) 32.76 (CH2), 126.37 (CH), 128.29 (CH,
2C), 128.43 (CH, 2C), 128.64 (CH, 2C), 128.82 (CH),
129.27 (CH, 2C), 132.45 (C), 136.28 (CH), 136.51 (CH),
138.24 (C), 143.50 (C), 144.68 (C), 187.08 (CvO), 187.65
(CvO); LRMS (EI) m/e 274 (M)þ; HRMS (EI) Calcd for
C17H14O2 (M)þ, 274.0994; Found 274.1003; Anal. Calcd
for C19H14O2: C, 83.19; H, 5.14. Found: C, 83.16; H, 5.33.
Regiochemistry was determined by the existence of H4–H5
1
coupling in H NMR (10.1 Hz).
4.2.6. 2-Benzyl-3-methyl-1,4-naphthoquinone. IR (KBr)
1663 (s), 1619 (w), 1592 (m), 1333 (s), 1293 (s), 716 (s); 1H
NMR (300 MHz, CDCl3) 2.25 (s, 3H), 4.04 (s, 2H), 7.16–
7.30 (m, 5H), 7.67–7.73 (m, 2H), 8.06–8.12 (m, 2H); 13C
NMR (75 MHz, CDCl3) 13.22 (CH3), 32.40 (CH2), 126.42
(CH3), 126.57 (CH), 126.63 (CH), 128.74 (CH, 2C), 128.80
(CH, 2C), 132.19 (C), 132.28 (C), 133.61 (CH), 133.64
(CH), 138.23 (C), 144.59 (C), 145.52 (C), 184.90 (CvO),
185.64 (CvO); LRMS (EI) m/e 262 (M)þ; HRMS (EI)
Calcd for C18H14O2 (M)þ, 262.0994; Found 262.0994;
Anal. Calcd for C18H14O2: C, 82.42; H, 5.38. Found: C,
82.26; H, 5.52.
4.2.2. Reaction of organotellurium compounds with
quinones. Typical experimental procedures. 2-Benzyl-
1,4-benzoquinone (7aA). A solution of benzyl p-methyl-
phenyl telluride (5a, 111 mg, 0.36 mmol) and 1,4-benzo-
quinone (6A, 78.0 mg, 0.72 mmol) in benzene (0.6 mL) in a
Pyrex tube was irradiated with a 200 W high pressure
mercury lamp at 1008C for 1 h. After the solvent was
removed under reduced pressure, the crude mixture was
purified by flush chromatography (silica gel 6.4 g; elution
with 5% ethyl acetate in hexane) to give 7aA in 57% yield
(40.4 mg). IR (neat) 1655 (s), 1599 (s), 1496 (s), 1454 (m),
4.2.7. 2-Hydroxy-3-benzyl-1,4-naphthoquinone. IR (KBr)
3345 (s, sharp), 1661 (s), 1644 (s), 1591 (m), 1371 (s), 1273
1
1
1352 (m), 704 (s); H NMR (300 MHz, CDCl3) 3.75 (d,
(m), 1223 (s); H NMR (300 MHz, CDCl3) 3.95 (s, 2H),
J¼1.2 Hz, 2H), 6.37 (m, 1H), 6.70 (dd, J¼9.9, 3.2 Hz, 1H),
7.18–7.36 (m, 5H); 13C NMR (75 MHz, CDCl3) 35.14
(CH2), 127.16 (CH), 129.00 (CH), 129.50 (CH, 2C), 133.41
(CH), 136.49 (CH, 2C), 136.79 (CH), 148.90 (C), 174.00
(CvO), 179.00 (CvO) (one sp2 carbon could not be
identified probably due to overlapping with other peaks.);
7.14–7.20 (m, 1H), 7.23–7.29 (m, 2H), 7.38–7.41 (m, 2H),
7.45 (br, s, 1H), 7.66 (dt, J¼7.5, 1.5 Hz, 1H), 7.74 (dt,
J¼7.5, 1.5 Hz, 1H), 8.06 (dd, J¼7.8, 1.5 Hz, 1H), 8.11 (dd,
J¼7.8, 1.5 Hz, 1H); 13C NMR (75 MHz, CDCl3) 28.98
(CH2), 123.11 (C), 126.19 (CH), 126.37 (CH), 126.96 (CH),
128.51 (CH, 2C), 129.26 (CH, 2C), 129.44 (C), 132.84 (C),

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S. Yamago et al. / Tetrahedron 58 (2002) 6805–6813
1
133.04 (CH), 135.07 (CH), 138.97 (C), 167.95 (C), 181.81
(CvO), 184.52 (CvO); LRMS (EI) m/e 264 (M)þ; HRMS
(EI) Calcd for C17H12O3 (M)þ, 264.0786; Found 264.0792;
Anal. Calcd for C17H12O3: C, 77.26; H, 4.58. Found: C,
82.26; H, 5.52.
(w), 1372 (m), 1225 (s), 1046 (m); H NMR (300 MHz,
CDCl3) 2.00 (s, 3H), 2.06, (s, 3H), 2.09 (s, 3H), 2.24 (s,
3H), 4.19 (dd, J¼12.9, 2.7 Hz, 1H), 4.45 (ddd, J¼9.6,
6.6, 2.7 Hz, 1H), 4.84 (dd, J¼12.9, 9.6 Hz, 1H), 5.12 (dd,
J¼3.9, 1.8 Hz, 1H), 5.24 (s, 1H), 5.33 (t, J¼3.3 Hz, 1H),
5.48 (dd, J¼6.6, 3.3 Hz, 1H), 6.73 (d, J¼2.1 Hz, 1H),
6.78 (dd, J¼9.9, 2.1 Hz, 2H); 13C NMR (75 MHz,
CDCl3) 20.45 (CH3), 20.57 (CH3), 20.62 (CH3), 20.83
(CH3), 59.04 (CH2), 63.94 (CH), 65.05 (CH), 67.13 (CH),
69.50 (CH), 72.69 (CH), 132.50 (CH), 136.38 (CH),
136.79 (CH), 144.15 (C), 169.23 (CvO), 169.64 (CvO),
169.67 (CvO), 171.08 (CvO), 185.56 (CvO), 187.20
(CvO); LRMS (FAB) m/e 439 (Mþ1)þ; Anal. Calcd
for C20H22O11: C, 54.80; H, 5.28. Found: C, 54.82; H,
5.28.
4.2.8. 2,3-Dimethoxy-5-methyl-6-prenyl-1,4-benzoqui-
none (7bC). IR (neat) 1649 (s), 1611 (s), 1264 (s), 1204
(m), 1154 (m), 1032 (m); 1H NMR (300 MHz, CDCl3) 1.68
(d, J¼0.9 Hz, 3H), 1.75 (s, 3H), 2.02 (s, 3H), 3.18 (br, d,
J¼7.2 Hz, 2H), 3.98 (s, 3H), 4.00 (s, 3H), 4.94 (triplet of
septet, J¼13.8, 0.9 Hz, 1H); 13C NMR (75 MHz, CDCl3)
11.84 (CH3), 17.89 (CH3), 25.37 (CH3), 25.67 (CH2), 61.15
(CH3, 2C), 119.12 (CH), 134.15 (C), 141.75 (C), 144.39 (C),
144.55 (C), 168.05 (C), 184.18 (CvO), 185.03 (CvO);
LRMS (EI) m/e 250 (M)þ; HRMS (EI) Calcd for C14H18O4
(M)þ, 250.1205; Found 250.1217.
4.2.14. (4-Hydroxyphenyloxy)-2,3,4,6-tetra-O-acetyl-D-
galactopyranoside (10). IR (KBr) 3400 (s, broad), 1752
(s), 1705 (s), 1599 (w), 1512 (s), 1374 (s), 1040 (s); H
1
4.2.9. 2-Methyl-3-prenyl-1,4-naphthoquinone. IR (neat)
1661 (s), 1619 (m), 1597 (s), 1375 (m), 1392 (s), 1296
(s), 713 (s); 1H NMR (300 MHz, CDCl3) 1.69 (d,
J¼0.9 Hz, 3H), 1.80 (d, J¼1.2 Hz, 3H), 2.19 (d,
J¼0.6 Hz, 3H), 3.36 (br, d, J¼6.9 Hz, 2H), 5.02 (triplet
of septet, J¼7.2, 1.4 Hz, 1H) 7.65–7.71 (m, 2H), 8.03–
8.10 (m, 2H); 13C NMR (75 MHz, CDCl3) 12.57 (CH3),
17.98 (CH3), 25.69 (CH3), 26.08 (CH2), 119.33 (CH),
126.30 (CH), 126.40 (CH), 132.27 (C) 132.29 (C), 133.42
(CH), 133.46 (CH), 134.07 (C), 143.42 (C), 146.20 (C),
184.75 (CvO), 185.66 (CvO); LRMS (EI) m/e 240
(M)þ; HRMS (EI) Calcd for C16H16O2 (M)þ, 240.1150;
Found 240.1139.
NMR (300 MHz, CDCl3) 1.98 (s, 3H), 2.03 (s, 3H), 2.10
(s, 3H), 2.17 (s, 3H), 4.04–4.16 (m, 2H), 4.39 (br, t,
J¼4.8 Hz, 1H), 5.26 (dd, J¼10.2, 3.6 Hz, 1H), 5.54 (s,
2H), 5.64 (d, J¼3.6 Hz, 1H), 6.77 (d, J¼9.0 Hz, 2H),
6.92 (d, J¼9.0 Hz, 2H); 13C NMR (75 MHz, CDCl3)
20.48 (CH3), 20.49 (CH3), 20.54 (CH3), 20.62 (CH3),
61.55 (CH2), 66.90 (CH), 67.56 (CH), 67.92 (CH), 67.95
(CH), 95.83 (CH), 116.09 (CH, 2C), 118.39 (CH, 2C),
150.25 (C), 151.83 (C), 170.40 (CvO), 170.52 (CvO),
170.75 (CvO, 2C); LRMS (FAB) m/e 440 (M)þ; Anal.
Calcd for C20H24O11: C, 54.54; H, 5.49. Found: C, 54.29;
H, 5.60.
4.2.10. 2-i-Propyl-1,4-benzoquinone (7bC)..18 1H NMR
(300 MHz, CDCl3) 1.14 (d, J¼6.9 Hz, 6H), 3.03 (doublet of
sept, J¼6.9, 1.3 Hz, 1H), 6.55 (s, 1H), 6.71 (dd, J¼10.2,
2.1 Hz, 1H), 6.77 (d, J¼10.2 Hz, 1H); LRMS (EI) m/e 150
(M)þ.
4.2.15. 5-Benzyl-2-t-butyl-1,4-benzoquinone and 3-
benzyl-2-t-butyl-1,4-benzoquinone. A solution of ben-
zyl p-methylphenyl telluride (5a, 111 mg, 0.36 mmol)
and 2-t-butyl-1,4-benzoquinone (118 mg, 0.72 mmol) in
benzene (0.6 mL) in a Pyrex tube was irradiated with a
250 W Hg lamp at 1008C for 1 h. After the solvent was
removed under reduced pressure, the crude mixture was
purified by flash chromatography (silica gel 6.5 g;
elution with 2% ethyl acetate in hexane) followed by
preparative GPC to give the title compounds as a 71:29
inseparable mixture in 78% yield (71.7 mg). IR (neat)
1651 (s), 1599 (m), 1366 (m), 1248 (m), 698 (m); 1H
NMR (300 MHz, CDCl3) 1.26 (s, 6.3H), 1.29 (s, 2.7H),
3.71 (d, J¼1.5 Hz, 1.4H), 3.74 (d, J¼1.5 Hz, 0.6H),
6.24 (dt, J¼2.4, 1.5 Hz, 0.3H), 6.26 (t, J¼1.5 Hz, 0.7H),
6.53 (d, J¼2.4 Hz, 0.3H), 6.59 (s, 0.7H), 7.16–7.36 (m,
5H); 13C NMR (75 MHz, CDCl3) 29.17 (CH3, major),
29.25 (CH3, minor), 34.49 (CH2, major), 35.05 (C,
major), 35.36 (C, minor), 35.55 (CH2, minor), 126.90
(CH, major), 128.80 (CH, major), 128.82 (CH, minor),
129.39 (CH, major), 131.38 (CH, minor), 131.60 (CH,
major), 132.08 (CH, minor), 135.34 (CH, major), 136.72
(C, major), 136.84 (C, minor), 146.94 (C, major),
150.40 (C, minor), 155.91 (C, major), 156.20 (C,
minor), 187.18 (CvO, minor), 187.89 (CvO, major),
188.26 (CvO, major), 188.41 (CvO, minor), (two sp2
carbon could not be identified probably due to
overlapping with other peaks.); LRMS (EI) m/e 254
(M)þ; HRMS (EI) Calcd for C17H18O2 (M)þ, 254.1307;
Found 254.1307. Regiochemistry was assigned by
coupling constant analyses in 1H NMR spectra and
4.2.11. 2-Methyl-3-i-propyl-1,4-naphthoquinone..5d IR
(KBr) 1465 (s), 1650 (s), 1593 (m), 1327 (m), 1296 (s),
1
720 (m); H NMR (300 MHz, CDCl3) 1.37 (d, J¼7.2 Hz,
6H), 2.22 (s, 3H), 3.27 (hept, J¼7.2 Hz, 1H), 7.62–7.73 (m,
2H), 7.95–8.15 (m, 2H); 13C NMR (75 MHz, CDCl3) 12.35
(CH3), 20.44 (CH3, 2C), 29.31 (CH), 125.98 (CH), 126.10
(CH), 131.74 (C), 132.74 (C), 133.04 (CH), 133.32 (CH),
142.65 (C), 151.34 (C), 184.83 (CvO), 185.62 (CvO),
LRMS (EI) m/e 414 (M)þ; HRMS (EI) Calcd for C14H14O2
(M)þ, 214.0994; Found 214.0994.
4.2.12. 2-(Methylphthalimido)-1,4-benzoquinone. IR
(KBr) 1774 (s), 1711 (s), 1670 (s), 1391 (s), 1321 (m),
1
957 (m); H NMR (300 MHz, CDCl3) 4.72 (d, J¼2.1 Hz,
2H), 6.38 (q, J¼2.2 Hz, 1H), 6.76 (dd, J¼10.1, 2.4 Hz,
1H), 6.83 (d, J¼10.1 Hz, 1H), 7.74–7.83 (m, 2H),
7.86–7.95 (m, 2H); 13C NMR (75 MHz, CDCl3)
35.77 (CH2), 123.81 (CH, 2C), 131.32 (CH), 134.35
(C), 134.60 (CH, 2C), 136.68 (CH), 167.63 (C), 186.40
(C), 186.91 (C); LRMS (EI) m/e 267 (M)þ; HRMS
(EI) Calcd for C15H9NO4 (M)þ, 267.0532; Found
267.0529.
4.2.13. 1-(10,40-Benzoquinon-20-yl)-2,3,4,6-tetra-O-acetyl-
a-D-galactopyranoside. IR (KBr) 1752 (s), 1661 (s), 1603

S. Yamago et al. / Tetrahedron 58 (2002) 6805–6813
6811
NOE spectra as shown below.
presence of internal standard indicated the formation of 13
in 87% yield.
4.3.1. p-Methylphenyl geranyl telluride (16). A solution
of 1,2-diiodoethane (620 mg, 2.2 mmol) in THF (22 mL)
was slowly added to samarium metal (662 mg, 4.4 mmol)
under a N2 atmosphere in a glove box at room temperature,
and the resulting mixture was stirred for 15 min. To this
mixture was added HMPA (3 mL) followed by di-p-
methylphenyl ditelluride (463 mg, 1.1 mmol), and the
resulting solution was stirred for 1 h. Geranyl bromide
(0.40 mL, 2.0 mmol) was added, and the resulting solution
was stirred for 1.5 h at room temperature. Heptane (50 mL)
was added, and the organic phase was washed repeatedly
with saturated aqueous sodium chloride, dried over MgSO4,
and evaporated to give a crude oil (881 mg), which was a
60:40 mixture of 16 and di-p-methylphenyl ditelluride. This
mixture was used in the following step without further
purification. 1H NMR (300 MHz, CDCl3) 1.54 (s, 3H), 1.70
(s, 3H), 1.79 (s, 3H), 1.98–2.44 (m, 4H), 2.44 (s, 3H), 3.71
(d, J¼8.4 Hz, 2H), 5.12–5.23 (m, 1H), 5.45–5.60 (m, 1H),
7.06–7.15 (m, 2H), 7.72–7.82 (m, 2H).
4.2.16. 2-Benzyl-1,4-naphthoquinone (13). A solution of
benzyl p-methylphenyl telluride (5a, 111 mg, 0.36 mmol)
and 1,4-naphthoquinone (114 mg, 0.72 mmol) in benzene
(0.6 mL) in a sealed Pyrex tube was irradiated with a 250 W
Hg lamp at 1008C for 1.5 h. After the solvent was removed
under reduced pressure, the crude mixture was purified by
flush chromatography (silica gel 5.4 g; elution with 4%
ethyl acetate in hexane) to give 13 in 54% yield (49.1 mg),
2-benzyl-2,3-dihydro-1,4-naphthoquinone (14) in 19%
yield (17.1 mg), and, 2,3-dibenzyl-1,4-naphthoquinone
(15) in 12% yield (15.0 mg).
4.3.2. Ubiquinone 2 (17). A solution of crude 16 containing
di-p-methylphenyl ditelluride (233.1 mg, 16/ditelluride
¼60:40, 0.36 mmol for 16) 2,3-dimethoxy-5-methyl-1,4-
benzoquinone (131 mg, 0.72 mmol) in benzene (0.6 mL) in
a sealed Pyrex tube was irradiated with a 250 W Hg lamp at
1008C for 2 h. After the solvent was removed under reduced
pressure, the crude mixture was purified by flash chroma-
tography (silica gel 8.2 g; elution with 15% ethyl acetate in
hexane) to give the title compound 17 in 41% yield (48 mg)
as a 72:28 mixture of trans and cis isomers. The 1H NMR of
the products was identical to that in the previous report.19 1H
NMR (300 MHz, CDCl3) 1.58 (s, 2.1H), 1.63 (s, 0.9H), 1.65
(s, 2.1H), 1.68 (s, 0.9H), 1.70 (s, 0.9H), 1.73 (s, 2.1H), 2.02
(s, 3H), 1.92–2.23 (m, 4H), 3.18 (d, J¼7.2 Hz, 2H), 3.980
(s, 0.9H), 3.985 (s, 2.1H), 3.995 (s, 0.9H), 3.998 (s, 2.1H),
4.90–4.98 (m, 1H), 5.00–5.07 (m, 0.7H), 5.11–5.19 (m,
0.3H).
13. IR (KBr) 1659 (s), 1592 (s), 1493 (m), 1330 (m), 1260
1
(m); H NMR (300 MHz, CDCl3) 3.90 (d, J¼1.2 Hz, 2H),
6.69–6.63 (m, 1H), 7.22–7.38 (m, 5H), 7.68–7.76 (m, 2H),
8.00–8.14 (m, 2H); 13C NMR (75 MHz, CDCl3) 35.62
(CH2), 126.13 (CH), 126.70 (CH), 127.02 (CH), 128.91
(CH, 2C), 129.50 (CH, 2C), 132.14 (C), 132.22 (C), 133.76
(CH), 133.81 (CH), 135.71 (CH), 136.80 (C), 150.96 (C),
185.12 (CvO), 185.28 (CvO); LRMS (EI) m/e 248 (M)þ;
HRMS (EI) Calcd for C17H12O2 (M)þ, 248.0837; Found
248.0831.
14. IR (KBr) 1684 (s), 1591 (s), 1497 (w), 1459 (w), 1422
1
(w), 1298 (w), 1266 (m), 720 (m); H NMR (300 MHz,
CDCl3) 2.74–2.88 (m, 2H), 3.02 (dd, J¼16.5, 5.4 Hz, 2H),
3.28–3.42 (m, 2H), 7.18–7.36 (m, 5H), 7.70–7.80 (m, 2H),
7.98–8.14 (m, 2H); 13C NMR (75 MHz, CDCl3) 36.36
(CH2), 42.30 (CH2), 49.04 (CH), 126.54 (CH), 126.77 (CH),
127.10 (CH), 128.72 (CH, 2C), 129.35 (CH, 2C), 134.23
(CH), 134.49 (CH), 135.15 (C), 135.24 (C), 138.11 (C),
196.05 (CvO), 197.98 (CvO); LRMS (EI) m/e 250 (M)þ;
HRMS (EI) Calcd for C17H14O2 (M)þ, 250.0094; Found
250.0093.
4.3.3. Vitamin K2(10) (18). A solution of crude 16
containing di-p-methylphenyl ditelluride (233.1 mg,
16/ditelluride¼60:40, 0.36 mmol for 16) 2-methyl-1,4-
naphthoquinone (124 mg, 0.72 mmol) in benzene (0.6 mL)
in a sealed Pyrex tube was irradiated with a 250 W Hg lamp
at 1008C for 1 h. After the solvent was removed under
reduced pressure, the crude mixture was purified by flash
chromatography (silica gel 10.6 g; elution with 5% ethyl
acetate in hexane) to give the title compound 18 in 44%
yield (49 mg) as a 73:27 mixture of the trans and cis
isomers. The 1H NMR of the products was identical to that
in the previous report.20 1H NMR (300 MHz, CDCl3) 1.49
(s, 2.1H), 1.55 (d, J¼1.2 Hz, 2.1H), 1.57 (s, 0.9H), 1.62 (d,
J¼1.5 Hz, 0.9H), 1.63 (d, J¼1.5 Hz, 0.9H), 1.71 (d,
J¼0.9 Hz, 2.1H), 1.82–2.21 (m, 4H), 2.11 (s, 2.1H), 2.12
(s, 0.9H), 3.29 (d, J¼6.9 Hz, 2H), 4.88–4.50 (m, 1.7H),
5.05–5.14 (m, 0.3H), 7.76–7.65 (m, 2H), 7.95–8.04 (m,
2H).
15. IR (KBr) 1659 (s), 1592 (m), 1493 (w), 1451 (w), 1293
(s), 723 (s); 1H NMR (300 MHz, CDCl3) 4.09 (s, 4H), 7.17–
7.28 (m, 10H), 7.66–7.73 (m, 2H), 8.04–8.12 (m, 2H); 13C
NMR (75 MHz, CDCl3) 32.34 (CH2, 2C), 126.55 (CH, 4C),
128.62 (CH, 2C), 128.74 (CH, 4C), 132.14 (C, 2C), 133.69
(CH, 2C), 138.05 (C, 2C), 146.30 (CvO, 2C), 185.34
(CvO, 2C); LRMS (EI) m/e 338 (M)þ; Anal. Calcd for
C24H18O2: C, 85.18; H, 5.36. Found: C, 85.05; H, 5.43.
4.3. Conversion of 14 into 13
A solution of 14 (25.0 mg, 0.1 mmol) and triethylamine
(3.6 mg, 0.036 mmol) in benzene-d6 (0.6 mL) was heated at
508C for 2 h under an argon atmosphere. After air was
passed through the reaction mixture for 0.5 h, the solvent
was removed. 1H NMR analysis of the crude mixture in the
4.3.4. Reaction of 5a with duroquinone. A solution of
benzyl p-methylphenyl telluride (5a, 558 mg, 1.8 mmol)
and duroquinone (296 mg, 1.8 mmol) in benzene (3 mL) in

6812
S. Yamago et al. / Tetrahedron 58 (2002) 6805–6813
a sealed Pyrex tube was irradiated with a 250 W Hg lamp at
1008C for 12 h. After the solvent was removed under
reduced pressure, the crude mixture was purified by flash
chromatography (silica gel 25 g; elution with 5% ethyl
acetate in hexane) followed by preparative GPC to give 5,6-
dibenzyl-2,3,5,6-tetramethyl-cyclohex-2-ene-1,4-dione (23,
237 mg), 5-benzyl-2,3,5,6-tetramethyl-cyclohex-2-ene-1,4-
dione (24, 83 mg), and 2,3,5-trimethyl-6-phenethyl-1,4-
benzoquinone (25, 77 mg) in 38, 18, 17% yields,
respectively.
References
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23. IR (KBr) 1674 (s), 1634 (m), 1495 (m), 1455 (m), 1374
(m), 764 (m), 702 (m); 1H NMR (300 MHz, CDCl3) 1.82 (s,
6H), 1.99 (s, 6H), 2.74 (d, J¼13.5 Hz, 2H), 2.82 (d,
J¼13.5 Hz, 2H), 6.77–6.84 (m, 4H), 7.14–7.30 (m, 6H);
13C NMR (75 MHz, CDCl3) 12.99 (CH3, 2C), 15.25 (CH3,
2C), 44.63 (CH2, 2C), 58.74 (C, 2C), 126.77 (CH, 2C),
127.96 (CH, 4C), 129.72 (CH, 4C), 136.31 (C, 2C), 142.90
(C, 2C), 202.29 (CvO, 2C); LRMS (EI) m/e 346 (M)þ;
HRMS (EI) Calcd for C24H26O2 (M)þ, 346.1933; Found
346.1922.
24. IR (KBr) 1678 (s), 1497 (m), 1374 (m), 737 (m), 702
1
(m); H NMR (300 MHz, CDCl3) 1.21 (s, 3H), 1.33 (d,
J¼6.9 Hz, 3H), 1.94 (s, 6H), 2.77 (d, J¼13.5 Hz, 1H), 2.80
(q, J¼6.9 Hz, 1H), 2.83 (d, J¼13.5 Hz, 1H), 6.82–6.92 (m,
2H), 7.15–7.18 (m, 3H); 13C NMR (75 MHz, CDCl3) 10.03
(CH3), 12.62 (CH3), 13.14 (CH3), 21.45 (CH3), 41.11
(CH2), 52.08 (CH), 54.16 (C), 126.68 (CH), 128.00 (CH,
2C), 129.84 (CH, 2C), 136.44 (C), 143.55 (C), 143.97 (C),
200.00 (CvO), 202.37 (CvO); LRMS (EI) m/e 256 (M)þ;
HRMS (EI) Calcd for C17H20O2 (M)þ, 256.1463; Found
256.1456.
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25. 1H NMR (300 MHz, CDCl3) 1.87 (s, 3H), 2.02 (s, 6H),
2.66–2.81 (m, 4H), 7.15–7.23 (m, 3H), 7.23–7.32 (m, 2H);
13C NMR (75 MHz, CDCl3) 11.89 (CH3), 12.24 (CH3),
12.30 (CH3), 29.04 (CH2), 34.78 (CH2), 126.10 (CH),
128.38 (CH, 4C), 140.38 (C), 140.44 (C), 140.79 (C),
141.13 (C), 142.99 (C), 186.99 (CvO), 187.58 (CvO);
LRMS (EI) m/e 254 (M)þ; HRMS (EI) Calcd for C17H18O2
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ution of p-methylphenyl p-chlorobenzoyl telluride (29ii,
215 mg, 0.60 mmol) and 1,4-benzoquinone (32.4 mg,
0.30 mmol) in acetonitrile (0.6 mL) in a Pyrex tube was
irradiated with a 250 W Hg lamp at 1008C for 3 h. After
the solvent was removed under reduced pressure, the
crude mixture was purified by recrystallization to give
30ii in 78% yield (91 mg).21 1H NMR (300 MHz,
CDCl3) 7.29 (s, 4H), 7.51 (d, J¼8.4 Hz, 4H), 8.15 (d,
J¼8.4 Hz, 4H); 13C NMR (75 MHz, CDCl3) 122.76
(CH, 4C), 127.94 (C, 2C) 129.17 (CH, 4C), 131.72
(CH, 4C), 140.48 (C, 2C), 148.51 (C, 2C), 164.42
(CvO, 2C); LRMS (EI) m/e 386 (M)þ.
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Acknowledgments
This work was partly supported by a Grant-in-Aid for the
Scientific Research from Japan Society for the Promotion of
Science.

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6813
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