Aromatic lithiation directed by the carboxylic acid groups. Synthesis of 9-substituted dibenzodioxin-1-carboxylic acids and 6-substituted phenoxathiin-4-carboxylic acids

Abstract

An efficient procedure has been developed for the regiospecific synthesis of 9-substituted dibenzo[ 1,4]diox- in-1-carboxylic acid derivatives. Lithiation of dibenzo[ 1,4]dioxin-l-carboxylic acid forms the lithium carboxylate, which directs subsequent metalation exclusively to the 9-position. Conditions for the controlled mono- and dilithiation of dibenzo[ 1,4]dioxin itself, leading to the direct synthesis of the corresponding mono- and isomeric dimethyl esters, are also described.