Transposition of Ketones via 2-Nitro Ketones

The reaction of 2-nitro ketones prepared by nitration of some cyclic ketones was investigated with the view toward transposing a carbonyl group to an adjacent carbon. Reduction of these 2-nitro ketones with sodium borohydride leads to 2-nitro alcohols, nitro olefins, or nitroalkanes, which in turn can be converted by various methods into ketones. In this manner cholestan-3-one was converted into cholestan-2-one via 2-nitrocholestan-3-one (2), its enol acetate (10), and 2β-nitrocholestane (5). 3β-Hydroxy-5-androsten-16-one was obtained from its 17-keto isomer via the 16-nitro 16-olefin. 2,2-Disubstituted cyclopentanones and cyclohexanones were transformed into the corresponding α-nitro ketones and borohydride reduction of the latter was studied. The chemistry of intermediate nitro compounds is discussed.