Photochemical transformations of dienes—VI : Photolysis of semicarbazone and oxime derivatives of 6-formyltestosterone methyl enol ether acetate

Abstract

Irradiation of syn-semicarbazone enol ether (IV) in methanol with 2537Å light leads to a mixture of syn-ketal (VI) and anti-ketal (VII); anti-semicarbazone enol ether (V) is also formed. Irradiation of IV with 3500 Å light leads very rapidly to an almost quantitative conversion to anti-semicarbazone enol ether (V). It therefore seems that excitation of the long wavelength band (313 mμ) of IV gives rise to syn ⇋ anti isomerization, whereas the short wavelength band (228 mμ) is responsible for ketalization. Irradiation of syn-oxime enol ether (VIII) leads to syn-oxime ketal (XI), anti-oxime ketal (XII), nitrile enol ether (X) and nitrile ketal (XIII). The formation of the latter two compounds constitutes, to our knowledge, the first example of a photo-dehydration of oximes to nitrile. anti-Oxime enol ether (IX) could only be obtained upon irradiation of VIII with 3500 Å light.