An Allenic Pauson−Khand-Type Reaction:  A Reversal in π-Bond Selectivity and the Formation of Seven-Membered Rings

Abstract

[reaction: see text] Treatment of alkynyl allenes with [Rh(CO)(2)Cl](2) results in a formal [2 + 2 + 1] cycloaddition reaction. This reaction occurs with complete regioselectivity for a variety of substrates affording only 4-alkylidene cyclopentenones in good yields. Moreover, seven-membered rings have been prepared in high yields.