Synthetic applications of chiral 1,3-dioxolan-4-ones and 3-acyloxazolidin-5-ones

Chiral dioxolanones derived from alpha-hydroxy acids can act as chiral acyl anion equivalents for addition to ethyl crotonate, nitroalkenes and butenolide. Subsequent flash vacuum pyrolysis results in loss of CO and (BuCHO)-C-t to give products. The related N-acyl and N-thioacyl-1,3-oxazolidin-5-ones formed from alpha-amino acids behave in a quite different way with loss of CO2 upon pyrolysis leading via N-(thio) acylaziridines to oxazolines and thiazolines. The stereochemistry of these transformations, both relative and absolute, is discussed and a mechanism involving an azomethine carboxylate intermediate is proposed.