Generation and Reaction of Monocarbonyliodonium Ylides:  Ester Exchange of (Z)-(β-Acetoxyvinyl)iodonium Salts with Lithium Ethoxide and Synthesis of α,β-Epoxy Ketones

Reported here for the first time are the generation of monocarbonyliodonium ylides and their alkylidene-transfer reactions to aldehydes yielding α,β-epoxy ketones. Exposure of ( Z )-(2-acetoxy-1-decenyl)iodonium bromide, prepared stereoselectively by sodium acetate-catalyzed Michael addition of acetic acid to (1-decynyl)(phenyl)iodonium salt, to EtOLi in THF at −78 °C results in ester exchange to generate the monocarbonyliodonium ylide with the liberation of ethyl acetate. 1 H NMR measurements indicate that the ylide is stable up to −30 °C in THF- d 8 but gradually decomposes at −20 °C to 1-bromo-2-decanone. The monocarbonyliodonium ylide acts as an alkylidene-transfer agent to carbonyl compounds, and the reaction with aldehydes in THF−DMSO at −30 °C gives α,β-epoxy ketones with E -isomers as a major product. With an α,β-unsaturated aldehyde, selective 1,2-addition to the carbonyl group was observed. The relative rates of the alkylidene-transfer reaction of this ylide for a series of ring-substituted benzaldehydes were measured. A Hammett correlation plot with the σ constants of substituents afforded the reaction constant ρ = 2.95 ( r = 1.00), which indicates that the monocarbonyliodonium ylide is moderately nucleophilic in nature.