Caglioti Reaction

Abstract The Caglioti reaction is the conversion of a carbonyl group in either ketones or aldehydes into a methylene group or an olefinic moiety with vicinal carbon by treatment of the corresponding p ‐tosylhydroazones of the ketones oraldehydes with a hydride base. When diborane is applied as a hydride source, the Caglioti reaction is often carried out for the reduction of α,β‐unsaturated ketones in the presence of acetic anhydride. It has been found that when diborane is generated in situ from NaBH 4 and BF 3 ·Et 2 O in diglyme while moisture and air are rigorously expelled from the reaction system, high yields of alkenes can be achieved from α,β‐unsaturated ketones. The higher reactivity of diborane in diglyme rather than in THF has been noticed. The LiAlH 4 can simultaneously remove the α‐nitro group and reduce the carbonyl group so that the p ‐tosylhydrazones of α‐nitroketones in THF can be directly converted into saturated hydrocarbons. When NaBH 4 is applied for the reduction of p ‐tosylhydrazones of ketones, the reactions are often refluxed in methanol or dioxane. Sodium cyanoborohydride (NaBH 3 CN) has been found to be mild and highly selective reagent and the catecholborane as the hydride source gives only a single hydrocarbon product on the reduction of the tosylhydrazones of ketones and aldehydes.