Catalytic, Cascade Ring-Opening Benzannulations of 2,3-Dihydrofuran O,O- and N,O-Acetals.

An Al(OTf)3 -catalyzed intramolecular cascade ring-opening benzannulation of 2,3-dihydrofuran O,O- and N,O-acetals is described. The cascade sequence involves the dihydrofuran ring-opening by acetal hydrolysis, an intramolecular Prins-type cyclization, and aromatization to generate an array of benzo-fused (hetero)aromatic systems in up to 95 % yield. This method represents the first example of dihydrofuran acetal usage in benzannulation reactions.

Catalytic, formal homo-Nazarov-type cyclizations of alkylidene cyclopropane-1,1-ketoesters: access to functionalized arenes and heteroaromatics.

A catalytic, formal homo-Nazarov-type cyclization of alkylidene cyclopropanes (ACPs) to give functionalized arenes and heteroaromatics is reported. In the presence of a Lewis acid catalyst, the ACP 1,1-ketoesters undergo distal bond cleavage to afford an allyl cation intermediate. Adjacent π-attack on the allyl cation then provides a six-membered ring that undergoes rapid aromatization.