Reactions of Periodate Under Homogeneous and Phase-Transfer Conditions: Examples of New Oxidations of Unusual Groups

Abstract

Reoently, we have described the use of tetrabutylamonium periodate (TBAPI) for the homogeneous oddations of sulfides, 2-hydroxyacids, 2-bromoketones and arylacetic acids^1,2. Oxidation by periodate of some of the above reported functional groups was not previously reported under classical conditions. Most likely, oince periodate anion is solubilized into organic solvents, interesting new features of this oxidizing specie can be obeerved. In order to extend our previuos obeervations, we have now examined the oxidation of benzylic halides by TBAPI. This reaction can be efficiently realized by several chramium reagents such as sodium chramete in HMPA³, potassium dichramate in polyethylene glyools⁴ or bis(tetrabutylammonium dichramate)⁵. It can be reasonably assumed that a nucleophilic displacement of halide by chramate or dichramate anion leads to a chramate ester, which rapidly collapses to the corresponding carbonyl campound⁶. We reasoned that in proper coinditions, also periodate anion could effect the same oxidation and treated benzyl bramide and chloride (la ald lc) with TBAPI. When the molar ratio TBAPI/halide was 1:1, the reaction prooeeded satisfactorily in refluxing dioxane, requiring 3 h for la and 8 h for lc. Yields of aldehyde 2a were 85 and 74% respectively. Also the bramide 1b was efficiently oxidized by TBAPI to ocetophenone 2b in refluxing dioxane (2 h, 78% yield).