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.

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[reaction: see text] Bromination and subsequent Suzuki reactions of 2-alkylidenetetrahydrofurans, readily available by [3+2] cyclizations, afforded 1'-(2''-methoxyphenyl)-2-alkylidenetetrahydrofurans. Treatment of the latter with boron tribromide and subsequent addition of water resulted in the chemoselective formation of functionalized benzofurans containing a remote bromide functionality. The products are formed by a new domino "ring-cleavage-deprotection-cyclization" reaction. The addition of an aqueous solution of potassium tert-butoxide, rather than water, afforded saturated analogues of calycine by a "ring-cleavage-deprotection-ring-closure-lactonization" reaction.

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