Photoinduced molecular transformations. Part 112. Transformation of steroids into ring- A -aromatized steroids and 19-norsteroids involving a regioselective β-scission of alkoxyl radicals; synthesis of two marine natural products, 19-nor-5α-cholestan-3β-ol and 19-norcholest-4-en-3-one, and new synthesis of estrone and 19-nortestosterone

A new transformation of steroids into 19-norsteroids and ring-A-aromatized steroids is described. The transformation method involves the removal of the 10β-methyl group by a regioselective β-scission of alkoxyl radicals. Cholesterol was transformed into two marine natural products, 19-nor-5α-cholestan-3β-ol and 19-norcholest-4-en-3-one, and into 19-norcholesta-1,3,5(10)-trien-3-ol. Transformations of 3β-hydroxyandrost-5-en-17-one into 19-nortestosterone, estrone, and the related estranes are also described.