Catalyst-free formation of 1,4-diketones by addition of silyl enolates to oxyallyl zwitterions in situ generated from α-haloketones

Reported here is the exclusive formation of 1,4-diketones by the uncatalyzed reaction of silyl enolates and alpha-haloketones. Enolates I are inherently more likely to react with alpha-haloketones II at the carbonyl carbon to produce halohydrin derivatives III or 2-(2-oxoethyl)-oxiranes IV. Thus, a variety of metal-catalyzed coupling reactions have been developed to avoid the undesired reaction when attempting the preparation of 1,4-diketones. We found that the oxyallyl zwitterions in situ generated from alpha-haloketones enabled the addition of silyl enolates to the alpha-carbonyl position to exclusively form 1,4-diketones in weakly basic conditions. Various types of silyl enolates and alpha-haloketones were applied to the catalyst-free coupling.