Convenient Synthesis of a Simple Coumarin from Salicylaldehyde and Wittig Reagent. II. : Synthesis of Bromo- and Methoxycarbonylcoumarins

Abstract

Reaction of salicylaldehydes (1) with carbethoxymethylenetriphenylphosphorane in diethylaniline under reflux gave coumarins (3) in moderate to high yield except 3-methoxycarbonylsalicyladehyde (1e) as summarized in Table I. The substituent effects are discussed. A substituent at C₆ on 1 usually facilitated the formation of the coumarin ring regardless of its electronic character.