Application of Magnesium Alkoxides to Syntheses of Benzoheterocyclic Compounds

Abstract

The Dieckmann condensation of methyl [(2-methoxycarbonyl)phenyl]-X-acetates Ia-Ih (X = O, S, SO2, NH, NCH3) initiated by action of magnesium methoxide, ethoxide, isopropoxide and other basic reagents have been studied under various conditions. Whereas magnesium methoxide has comparable efficiency as sodium methoxide and potassium tert-butoxide in syntheses of benzoheterocyclic compounds IIa-IIh, magnesium ethoxide gives the ethyl ester IIb in medium yield, and magnesium isopropoxide is quite inefficient in the condensation reaction. The alkylation of the esters IIa, IId, and IIg with methyl chloroacetate in the presence of sodium hydride in dimethylformamide gives the diesters IIi - IIk which on action by potassium tert-butoxide undergo the cyclization reaction to give esters III.