Diastereoselectivity control in formal nucleophilic substitution of bromocyclopropanes with oxygen- and sulfur-based nucleophiles.

A diastereoconvergent formal nucleophilic substitution of bromocyclopropanes with oxygen- and sulfur-based nucleophiles is described. The reaction proceeds via in situ formation of a highly reactive cyclopropene intermediate and subsequent diastereoselective addition of a nucleophile across the strained C═C bond. Three alternative means of controlling the diastereoselectivity of addition have been demonstrated: (1) thermodynamically driven epimerization of enolizable carboxamides, (2) steric control by bulky substituents, and (3) directing effect of carboxamide or carboxylate functions.