The mechanism of the barton reaction

Abstract

Photolysis of 6β-nitroso-oxy-5α-cholestan-3β-yl acetate gave the 19-oxime, 6β,19-oxide, 6-oxo-5α-cholestan-3β-yl apetate, and 6β-hydroxy-5α-cholestan-3β-yl acetate. The 6β.19-oxide was formed from the C-19 nitrosodimer by a novel photochemical reaction involving nitric oxide and with subsequent displacement of the presumed 19-diazonium salt by the 6β-hydroxy-function. The formation of ketone was coupled with the appearance of hyponitrous acid. The alcohol was formed by intermolecular hydrogen atom abstraction by the intermediate C-19 alkyl radical in a reaction not related to ketone formation. Evidence for the intermediacy of peroxynitrites in the formation of nitrate esters by nitrite photolysis under oxygen is presented. Hydroperoxides and nitrosyl chloride gave the derived nitrates. Attention is drawn to the formation of androst-4-ene-3,17-dione (59%) from reaction of trifluoroacetic anhydride and 17α-hydroperoxyprogesterone.