1980 Volume 53 Issue 8 Pages 2292-2296
Irradiation of D-nor-5α-androstan-16-one oxime in methanol leads to a mixture of seco-nitriles; D-nor-13,16-seco-5α-androst-13(18)-ene-16-nitrile (3), D-nor-13,16-seco-5α-androst-12-ene-16-nitrile (7), 13ξ-methoxy-D-nor-13,16-seco-5α-androstane-16-nitrile (8), and 15-hydroxy-D)-nor-15,16-seco-5α-androstane-16-nitrile (9). These result from ionic α-fissions at either of the α-bonds. Low yields of three lactams, 17-aza-5α-androstan-16-one (6), 17-aza-5α,13α-androstan-16-one (11), and 16-aza-5α-androstan-17-one (5), resulting from photo-Beckmann rearrangement, are also formed. The formation of 11 is the second proven example of a photo-Beckmann rearrangement in which a chirality of the migrating carbon center is not retained in the product lactam and an intervention of a ring-opened intermediate must be involved. It was found that direction of the α-cleavage of this excited four-membered cyclic ketone oxime was not governed only by the stability of cleaved ions, since seco-nitrile 9 resulting from α-fission to a less stable primary carbonium ion was formed together with seco-nitriles 3, 7, and 8 from a more stable tertiary carbonium ion. The Beckmann rearrangement of the mixture of syn and anti oximes with thionyl chloride afforded the two expected lactams 5 and 6 together with the products of Beckmann fission 3 and D-nor-13,16-seco-5α-androst-13(14)-ene-16-nitrile resulting from a cleavage to tertiary carbonium ion.
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