T. Mizuno et al. / Tetrahedron Letters 43 (2002) 7765–7767
7767
alcohol (2a) (1.03 mL, 10 mmol), powdered sulfur (481
mg, 15 mmol), DBU (2.24 mL, 15 mmol), and THF (10
mL) were placed with a magnetic stirring bar under an
argon atmosphere. The autoclave was then flushed three
times with carbon monoxide and finally charged with
carbon monoxide at 1.0 MPa at 20°C. The reaction was
carried out at 80°C for 6 h with vigorous stirring. After
cooling down and evacuation of carbon monoxide,
methyl iodide (0.93 mL, 15 mmol) was added at 0°C
under an argon atmosphere. The reaction mixture was
stirred for an additional 16 h under ambient pressure, at
20°C. Then, the resulting mixture was poured into 1N
HCl (100 mL) and extracted with t-butyl methyl ether
(100 mL, 3×50 mL). After evaporation of solvents and
purification by short-column chromatography (silica gel,
toluene:AcOEt=1:1), S-methyl O-benzyl carbonothioate
(3a) was afforded in an 89% yield (1.62 g). S-Methyl
17. Typical procedure for the synthesis of S-methyl O-benzyl
carbonothioate (3a) by the carbonylation with carbonyl
sulfide is as follows. A THF solution (50 mL) containing
benzyl alcohol (2a) (10.3 mL, 100 mmol) and DBU (22.4
mL, 150 mmol) was vigorously stirred under carbonyl
sulfide (0.1 MPa) at 20°C for 1 h. Into the THF solution
of carbonothioate salt, methyl iodide (7.5 mL, 120 mmol)
was added slowly at 0°C under an argon atmosphere. The
reaction mixture was stirred for an additional 2 h at
20°C. The resulting mixture was then poured into 1N
HCl (100 mL) and extracted with t-butyl methyl ether
(3×100 mL). After evaporation of solvents and purifica-
tion by vaccum distillation, S-methyl O-benzyl car-
bonothioate (3a) was obtained in an 87% yield (15.76 g).
18. General procedure for the synthesis of benzyl chlorofor-
mate (1a) by the chlorination of 3a with sulfuryl chloride
is as follows. Into neat S-methyl O-benzyl carbono-
thioate (3a) (3.64 g, 20 mmol), sulfuryl chloride (2.41 mL,
30 mmol) was added slowly at 0°C under an argon
atmosphere. The reaction mixture was stirred for an
additional hour at 20°C. After evaporation of volatile
compounds (SO2Cl2 and MeSCl), benzyl chloroformate
(CbzCl) (1a) was given in a 100% yield (3.41 g) as an
almost pure form. After further purification by vacuum
distillation accompanied with a partial decomposition, 1a
was obtained in a 72% yield (2.47 g). Benzyl chlorofor-
O-benzyl carbonothioate (3a): IR (neat) 1710, 1135 cm−1
;
1H NMR (300 MHz, CDCl3) l 2.35 (s, 3H), 5.24 (s, 2H),
7.36 (s, 5H); 13C NMR (75 MHz, CDCl3) l 13.4, 68.9,
128.3, 128.4, 128.5, 135.2, 171.6; MS (m/z, %) 182 (M+,
69), 92 (48), 91 (100), 77 (27), 65 (36); exact MS calcd for
C9H10O2S: 182.0402. Found: 182.0368.
12. Mizuno, T.; Nishiguchi, I.; Hirashima, T.; Ogawa, A.;
Kambe, N.; Sonoda, N. Tetrahedron Lett. 1988, 37,
4767–4768.
13. Carbonyl sulfide is a useful synthetic agent for the intro-
duction of the thiocarbonyl functionality into various
organic molecules.14 Generally, carbonyl sulfide is pro-
duced from carbon monoxide and sulfur at high tempera-
ture.15 We also developed the carbonyl sulfide synthesis
using carbon monoxide with sulfur in the presence of
selenium catalyst under mild conditions.16
14. Mori, K.; Shimizu, M.; Kanazawa, T. J. Syn. Org. Chem.
Jpn. 1971, 29, 609–615.
15. Nakayama, Y.; Sano, H.; Okamura, S.; Hirao, K.
Japanese Patent 131993, 1977. Chem. Abstr. 1978, 88,
63801.
1
mate (CbzCl) (1a): IR (neat) 1780, 1145 cm−1; H NMR
(300 MHz, CDCl3) l 5.30 (s, 2H), 7.40 (s, 5H); 13C NMR
(75 MHz, CDCl3) l 73.4, 128.8, 128.9, 129.3, 133.3,
150.6; MS (m/z, %) 172 (28), 170 (M+, 80), 91 (100), 90
(35).19
19. Identification of benzyl chloroformate (CbzCl) (1a) was
performed by comparison of the spectra of 1a with those
of commercially available authentic sample.
20. Thermal instability of benzyl chloroformate (1a) to
decompose into benzyl chloride and carbon dioxide is
well known.21
21. Merck Index, 1996, 12, 1848.
22. Folkmann, M.; Lund, F. J. Synthesis 1990, 1159–1166.
23. Gilligan, W. H.; Stafford, S. L. Synthesis 1979, 600–602.
16. Mizuno, T.; Nishiguchi, I.; Hirashima, T.; Sonoda, N.
Heteroatom Chem. 1990, 1, 157–159.