Substituent effects in the BF3-mediated acylation of phenols with cinnamic acids.

2',4'-Dihydroxy-4-nitrochalcone was obtained by BF3 etherate acylation of resorcinol with 4-nitrocinnamic acid. Instead, when p-methoxycinnamic or p-coumaric acids were used, the main product of the reaction was the coumarin umbelliferone, while no chalcone was present. These effects are commented in relation to the nature of the substituent present on the cinnamic acid moiety.