A Cascade Approach to Naphthalene Derivatives from o-Alkynylbenzaldehydes and Enolizable Ketones via in-situ-Formed Acetals

Abstract

Using the in-situ-formed acetal strategy, a facile approach has been developed to synthesize naphthalene derivatives from o-alkynylbenzaldehydes and enolizable ketones. In situ acetal formation assists the condensation between o-alkynylbenzaldehydes and enolizable ketones to give chalcone derivatives under Brønsted acidic conditions. In situ acetal formation facilitates the reaction by increasing the electrophilicity of the carbonyl carbon of the o-alkynylaldehyde through oxonium ion formation, and also by enhancing the nucleophilicity of the α carbon of the ketone through the formation of an enol ether. The formed chalcones undergo trans to cis isomerization to effect alkyne-carbonyl metathesis to give naphthalene derivatives.