Mild dehalogenative reduction of tri- and di-halogenomethyl compounds to lower halides by nickel tetracarbonyl.

Abstract

Nickel carbonyl in tetrahydrofuran reductively converts polyhalomethyl groups into di-(or mono-) halomethyls in high to moderate yields under quite mild conditions. Polyhalides studied here include type 1 telomers, arising from the radical reaction of vinylene carbonate and polyhalomethanes, whose successful reduction to gem-dihalides opens up a new route to aldo-sugars. Tetrahydrofuran is the most effective for the reduction among the solvents examined such as isopropanol, dioxane, tetrahydrothiophene, cyclohexene (-hexane) and benzene, while dimethylformamide gives the entirely different products like the olefines (9, 10) and the carboxylic acids (11, 12). The plausible mechanisms involving radical and carbene intermediates are discussed for the reactions in both solvents.