Tertiary Amine Catalyzed Annulation Route to Tetrasubstituted Pyrans

Significance

Reported is the synthesis of tetrasubstituted pyrans 3 via the tertiary amine catalyzed annulation of allenes 1 with ketones 2. A ­variety of EWGs may be incorporated into C3 of pyrans 3, with both aliphatic and (hetero)aromatic ketones also tolerated. Fused bi- and tricyclic products 7 and 8 are readily accessible using this method. Furthermore, diamines were shown to be efficient nucleophiles, delivering six-, seven-, and eight-membered ring products 9-11 in high yields. A mechanism is proposed as evidenced by the isolation of intermediate 6 when using ­benzene as solvent.