Convenient synthesis of ε-halo-β-ketoesters and γ,γ′-dibromoalkanones by regio- and chemoselective reaction of 2-alkylidenetetrahydrofurans with boron trihalides:: A "ring-closure/ring-cleavage" strategy

The reaction of boron tribromide and boron trichloride with 2-alkylidenetetrahydrofurans, readily available on the basis of cyclizations of free and masked dianions with 1,2-dielectrophiles, allowed an efficient synthesis of a variety of carbonyl compounds with remote halide functionality. This includes the chemo- and regioselective synthesis of 6-bromo- and 6-chloro-3-oxoalkanoates and 1,7-dibromoheptan-4-ones. The approach outlined herein can be regarded as a "ring-closure/ring-cleavage" strategy.