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The Synthesis and Chemistry of 2-Nitrocyclohexanones

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Description: 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.
Language: English
Format: Degree Work