Fluorine-Containing Butanolides and Butenolides. Vinylic Fluorine Displacement in 4,4-Dialkyl-2,3-difluoro-2-buten-4-olides and a Novel Rearrangement Induced by Organolithium Addition to a Carbonyl Group

2,3-Difluoro-4,4-dimethyl-2-buten-4-olide (1) and spirocyclic 2,3-difluoro-4,4-(pentane-1,5-diyl)-2-buten-4-olide (2) were modified by vinylic displacement of fluorine with some O- and C-nucleophiles. Sodium and lithium alkoxides, substituted phenoxides and protected glucose alkoxides reacted by 1,4-addition followed by the expulsion of fluoride ion to give 3-substituted derivatives (4–24). Softer Grignard reagents in the form of a copper (I) bromide-dimethyl sulfide complex reacted in the same way as O-nucleophiles to afford 3-alkyl- or 3-aryl derivatives (25–26). Harder organolithium reagents attacked the carbonyl group to give unstable hydroxy compounds that rearranged spontaneously to furan(2H)-3-ones (27–29) in a novel oxygen rearrangement reaction.