γ-Lactonizations of 2H-chromenes via cyclopropanation

A two-step synthesis of tetrahydro-2H-furochromenones from 2H-chromenes is reported. The reaction of a series of tert-butyl 2-diazoacetate derivatives with 2H-chromenes, catalyzed by Rh2(OAc)4, generated cyclopropane intermediates that rearranged to γ-lactones on treatment with Sn(OTf)2.

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