Gold-Catalyzed Cyclizations of 4-Alkyl-2-yn-1-yl (Oxy)cyclohexa-2,5-dien-1-ones ( <b>1</b> ) to Develop Two Cyclizations via π-Alkyne versus π-Allene Activations

This work reports two new gold-catalyzed cyclizations of 4-alkyl-2-yn-1-yl (oxy)cyclohexa-2,5-dien-1-ones (<b>1</b>) via gold-π-allene versus gold-π-alkyne routes, The π-allene route involves a [3.3] Claisen rearrangement of 1-alloxyallene intermediates to enable a 1,3-group migration, ultimately affording 2-substituted 3-formylbenzofurans (<b>2</b>). Density functional theory (DFT) calculations support this proposed mechanism in which water plays a key role. An alternative π-alkyne route contains cocatalyst PhNH₂ (10 mol %), leading to the formation of C_3,4-fused tetrahydrobenzofuran-5(4<i>H</i>)-ones (<b>3</b>) stereoselectively.