Rhodium-catalyzed intramolecular hydroacylation of 4-alkynals

Abstract

A novel intramolecular trans-hydroacylation of 4-alkynals leading to cyclopentenones was accomplished by using a cationic rhodium (I) complex. We also developed three types of new reactions, 1) reaction of 4-alkynals with phenol to provide cis-4-alkenoates, 2) [4+2] cycloaddition of 4-alkynals with alkynes to provide cyclohexenones, and 3) isomerization of 4-alkynals to 1, 3-dienals, through five-membered rhodium metallacycles generated from 4-alkynals. The asymmetric variants of this intramolecular hydroacylation reaction were successfully developed by using 3-methoxy-4-alkynals as the substrates. The present method represents an attractive new route to highly functionalized cyclopentenones and cyclobutanones.