A Cascade Approach to Naphthalene Derivatives from <i>o</i>‐Alkynylbenzaldehydes and Enolizable Ketones via in‐situ‐Formed Acetals

Abstract

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.