Reaction of 3-phenylglycidic esters. Part 1. Stereoselective opening of the oxirane ring of trans-3-phenylglycidic esters with 2-nitrothiophenols and the effect of various catalysts thereon

Abstract

In the reaction of 2-nitrothiophenol (2) with trans-3-phenylglycidic esters carrying various substituents on the benzene ring, both reactivity and stereoselectivity of the oxirane ring-opening of the glycidates were markedly influenced by the electronic nature of the substituents. The presence of electron-donating groups was favourable for both reactivity and the preferential formation of cis-opening products, while the reverse was true for electron-withdrawing groups. As a result of our investigation on the catalytic effect of various Lewis acids in the reaction of the 4-methoxy derivative (1) with (2), tin compounds were found to be effective catalysts for cis-opening and readily produced the threo-nitro ester (3a), a key intermediate for the synthesis of diltiazem (5).

Isolation of the crystalline complex (adduct A) from the reaction of (2) with SnCl₄ and its efficient catalytic activity similar to that of SnCl₄ suggest that the transition state involves co-ordination of tin derivatives both with (2) and the epoxy oxygen of (1) to cause highly specific cis-opening.