Construction of Complex 1,3-Cyclohexadienes via Phosphine-Catalyzed (4 + 2) Annulations of δ‑Acetoxy Allenoates and Ketones

The phosphine-catalyzed substrate-dependent (4 + 2) annulations of δ-acetoxy allenoates with ketones is described. Allenoates <b>1</b> with an alkyl substituent at δC are able to react with cyclic 1,3-diketones <b>2</b>, wherein the δC is attacked by the methenyl carbon of <b>2</b> while the αC attacks the ketone of <b>2</b>. Allenoates <b>5</b> with an aryl group at δC is poised to react with cyclic β-carbonyl amides <b>6</b>, in which the αC is attacked by the methenyl carbon of <b>6</b> and the δC undergoes 1,2-addition to the ketone of <b>6</b>.