THE SYNTHESIS AND CHEMISTRY OF 2-NITROCYCLOHEXANONES

Nitration of the most substituted (thermodynamically more stable) enol acetate or trimethylsilyl enol ether of 2-methylcyclohexanone and the phase-transfer methylation of 2-nitrocyclohexanone serve as methods of preparation of 2-methyl-2-nitrocyclohexanone, whereas nitration of the least substituted enol acetate or trimethylsilyl enol ether of 2-methylcyclohexanone and methylation of the dianion of 2-nitrocyclohexanone lead to cis- and trans-6-methyl-2-nitrocyclohexanone. Nitration of the enol acetate or trimethylsilyl enol ether of 2,6-dimethylcyclohexanone and methylation of either 2-methyl-2-nitro- or 6-methyl-2-nitrocyclohexanone are methods of preparation of cis- and trans-2,6-dimethyl-2-nitrocyclohexanone.; Reduction of 2-nitrocyclohexanones with sodium borohydride in ethanol and sodium cyanoborohydride in methanol-hydrochloric acid gave different ratios of stereoisomeric 2-nitrocyclohexanols. Reduction with sodium borohydride also caused side reactions such as elimination in that case of C-2-unsubstituted 2-nitrocyclohexanones and ring fragmentation in the case of C-2-substituted 2-nitrocyclohexanones.; Treatment of the 2-nitrocyclohexanols with sodium hydride and subsequent acidification of the salts leads to the regioselective synthesis of conjugated nitrocyclohexenes.; ('1)H NMR chemical shift and coupling constant data were used to determine the configurations and the preferred conformations of the nitrocyclohexanones and nitrocyclohexanols.; The following are generalizations about the reactions studied in this investigation: (1) The nitration of cyclohexanone enol acetates with a mixture of trifluoroacetic anhydride and ammonium nitrate in chloroform is the best method for the preparation of (alpha)-nitrocyclohexanones. (2) The chemoselective reduction of (alpha)-nitrocyclohexanones to (beta)-nitrocyclohexanols can be achieved by either using sodium borohydride in ethanol or sodium cyanoborohydride in methanol at pH 3 as the reducing conditions. (3) Conjugated nitrocyclohexenes are readily prepared from (beta)-nitrocyclohexanols by reaction with one equivalent of sodium hydride following by acidification to pH 1.