Chemoselective, regioselective, and E/Z-diastereoselective synthesis of 2-alkylidenetetrahydrofurans by sequential reactions of ambident dianions and monoanions

A number of novel beta-ketoesters were prepared by regioselective alkylation reactions of simple beta-ketoester dianions. The cyclization of the dianions of these 1,3-dicarbonyl derivatives with 1-bromo-2-chloroethane afforded a variety of 2-alkylidenetetrahydrofurans with very good regioselectivity and E/Z-diastereoselectivity. These products were deprotonated to give novel ambident carbanions. The alkylation of these carbanions with alkyl halides proceeded with very good regioselectivity and E/Z-diastereoselectivity and allowed a convenient synthesis of a great variety of new 2-alkylidenetetrahydrofurans.