A-Hydroxythiolic acid esters

N-Methy Ipyrrolidinelmagnesium nitrate a-Hydroxythiolic acid esters from l-hydroxy-2-ketothioethers... 

Glycidic from a-bromo-p-hydroxythiolic acid esters... 

A soln. of /er/-butyl bromothioacetate in dichloromethane at —78° treated via syringe with 1.1 eqs. dicyclopentylborinyl triflate in the same solvent followed by 1.2 eqs. of /-Pr2NEt, stirred at —78° for 30 min, a soln. of 2,3-dimethoxybenzaldehyde in dichloromethane added slowly, stirred for a further 2 h at the same temp., 1.2 eqs. /-Pr2NEt added, the mixture warmed to room temp., and stirred for 12 h - / r/-butyl (2R, 3S )-2,3-epoxy-3-(2,3-dimethoxyphenyl)thiopropanoate. Y 62%. This method gives higher /ra 5-selectivity than the classical Darzens glycidic ester condensation. F.e. and isolation of the intermediate a-bromo-P-hydroxythiolic acid esters, also conversion to glycidic acid esters (with Mg(OMe)2) s. R.P. Polniaszek, S.E. Belmont, Synth. Commun. 19, 221-32 (1989). 

A variety of 9-ketals were prepared from either methyl ester 245 (obtained from I-PGA2 diester 21 by hydrogenation followe3 by selective hydrolysis) or acid 2, by the usual ketalization techniques involving treatment of the ketone with an excess of the requisite diol, dithiol or hydroxythiol in the presence of an acid catalyst (109). Saponification of the ester afforded the corresponding acids listed in Table IV. [A recent report from the Upjohn laboratories describes the facile preparation of the ethylene ketal of PGE2 (110). 1... 

---