the possibility that 2 might act as an effective reagent for the
sulfenylation of various nucleophiles under mild conditions.
The starting quinone mono-O,S-acetals 2a–c were prepared by
Pummerer reaction of the corresponding sulfoxide 1 with
1-ethoxyvinyl esters.4 A higher yield was obtained with 2b and
2c than 2a (Scheme 1).3
Footnotes
* E-mail: kita@em.phs.osaka-u.ac.jp
† Typical procedure: a mixture of 4 (1 mmol), 2a–c (1 mmol) and
Me3SiOSO2CF3 (cat.) in MeCN (5 ml) was stirred at room temperature
under a positive atmosphere of dry nitrogen. After 10 min, the mixture was
concentrated in vacuo. Purification by column chromatography on silica gel
(eluent: AcOEt–hexane = 1:5) gave 5a–c in 94–99% yield.
First we examined the ability of quinone mono-O,S-acetals
2a–c for sulfenylation by the use of cyclic silyl enol ethers 4a,b
and found that 2a–c were excellent sulfenylating reagents which
gave the target thioethers in quantitative yields (Table 1, entries
1–4).† The generality of this sulfenylation reaction was
confirmed using various acyclic silyl enol ethers 6a–e with 2b
(Table 1, entries 5–9). This sulfenylating reagent also reacted
easily with electron-rich aromatic compounds such as 8a–e and
heteroaromatic compounds 10a–c, and the corresponding
thioethers were obtained by direct sulfenylation (Table 1,
entries 10–17). These sulfenylation reactions were completed
within 10 min at 230 °C to room temperature under nearly
neutral conditions, giving thioether derivatives in almost
quantitative yields. In addition, as a side product, the hydro-
quinone derivative 3 was easily removed by treatment with
weak aqueous alkali.
References
1 For recent reviews, see R. D. Norcross and I. Paterson, Chem. Rev., 1995,
95, 2041; D. J. Faulkner, Nat. Prod. Rep., 1995, 12, 223.
2 For example: H. Behforouz and J. E. Kerwood, J. Org. Chem., 1969, 34,
51; E. J. Corey and S. Knapp, Tetrahedron Lett., 1976, 4687;
R. J. Goodridge, T. W. Hambley, R. K. Haynes Gilbert and W. C.
Berkeley, Jr., J. Am. Chem. Soc., 1974, 96, 5495; P. G. Gassman,
D. P. Gilbert and S. M. Cole, J. Org. Chem., 1977, 42, 3233; D. Scholz,
Synthesis, 1983, 944; D. Scholz, Liebigs Ann. Chem., 1984, 259;
S. Andreades, J. F. Harris, Jr. and W. A. Sheppard, J. Org. Chem., 1964,
29, 898; R. M. Scribner, J. Org. Chem., 1966, 31, 3671; H. P. Kaufman
and K. Kuchler, Chem. Ber., 1934, 67B, 944; Y. Tamura, S. Kwon,
M. W. Chun and M. Ikeda, J. Heterocycl. Chem., 1978, 15, 425;
K. Tomita, A. Terada and R. Tachikawa, Heterocycles, 1976, 4, 733;
D. S. Reno and R. J. Pariza, Org. Synth., 1996, 74, 124.
In conclusion, we have succeeded in developing novel
sulfenylating reagents by taking advantage of activation on the
sulfur atom based on aromatization. These reagents might be
applied to the synthesis of biologically active substances having
sulfur functions and labile functions that are sensitive to basic or
acidic conditions.
3 Y. Kita, Y. Takeda, M. Matsugi, K. Iio, K. Gotanda, K. Murata and
S. Akai, Angew. Chem., Int. Ed. Engl., in the press.
4 Y. Kita and N. Shibata, Synlett, 1996, 273; N. Shibata, M. Matsugi,
N. Kawano, S. Fukui, C. Fujimori, K. Gotanda, K. Murata and Y. Kita,
Tetrahedron: Asymmetry, 1997, 8, 303.
Received in Cambridge, UK, 29th April 1997; 7/02912H
1388
Chem. Commun., 1997
Matsugi, Masato
