Reactions of 2, 2, 4-trimethyl-1, 3-oxathiolan-5-one (lb) with alkyl halides in the presence of LDA and HMPA give alkylation products only with very reactive halides. In contast, 2, 2- dimethyl-l, 3-oxathiolan-5-one(la) affords no alkylation products. Both la and lb react with aldehydes and ketones to give diastereomeric mixtures of aldol products. Conjugated enones afford predominantly 1, 2-or 1, 4-addition depending on the structure of the ...