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.