Photoinduced molecular transformations. Part 98. The photochemistry of steroidal 6-membered cyclic .ALPHA.-nitro ketones.

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  • Suginome Hiroshi
    Organic Synthesis Division, Department of Chemical Process Engineering, Faculty of Engineering, Hokkaido University
  • Kurokawa Yoshitaka
    Organic Synthesis Division, Department of Chemical Process Engineering, Faculty of Engineering, Hokkaido University
  • Orito Kazuhiko
    Organic Synthesis Division, Department of Chemical Process Engineering, Faculty of Engineering, Hokkaido University

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  • The Photochemistry of Steroidal 6-Membered Cyclic α-Nitro Ketones

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The results of the photolysis of five steroidal 6-membered cyclic α-nitro ketones in ethanol are described. Irradiation with a Pyrex-filtered light of 2-nitro-5α-cholestan-3-one in ethanol, which exists exclusively in the enol form in the solvent, resulted in a new photorearrangement and gave 5α-cholestane-2,3-dione 3-oxime with the accompanying formation of the corresponding α-diketone. We propose a path involving a nitro–nitrite rearrangement for this anomalous formation of 5α-cholestane-2,3-dione 3-oxime. However, similar irradiation of 4,4-dimethyl-2-nitro-5α-choloestan-3-one, which exists exclusively as the enol form in ethanol, and 3-nitro-5α-cholestan-2-one, which is in an 1 : 1 equilibrium mixture of keto and enol forms in ethanol, gave the corresponding α-hydroxyimino ketone and α-diketone respectively. Irradiation of 4β-nitro-5β-cholestan-3-one and 6α-nitro-5α-cholestan-7-one, both of which exist as the keto form in ethanol, gave similarly the corresponding α-hydroxyimino ketone respectively, but without the accompanying formation of α-diketone. The α-hydroxyimino ketones from the above four 6-membered cyclic α-nitro ketones arise through the hydrogen abstraction by the n,π* excited nitro group of the keto forms of the α-nitro ketones followed by the elimination of the element of water, while α-diketones are formed via the nitro–nitrite rearrangement of the excited nitro group of the enol forms.

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