Photoinduced molecular transformations. Part 106. Intramolecular addition vsβ-scission of oxyl radicals generated from A-homo-5α-cholest-1-en-4α- and -4β-ol hypoiodites and 4-methyl-A-homo-5α-cholest-1-en-4α- and -4β-ol hypoiodites

Abstract

Photoinduced reaction of A-homo-5α-cholest-1-en-4α-ol hypoiodite or the corresponding 4β-methyl derivative resulted in the formation of the two formates or the two corresponding acetates which arose from successive reactions of the radical intermediates generated from β-scission of the corresponding alkoxyl radicals. The photoinduced reactions of the hypoiodites of the isomeric 4β-ol or its 4α-methyl derivative, on the other hand, respectively gave 1β,4β-epoxy-2α-iodo-A-homo-5α-cholestane or its 4α-methyl derivative produced by intramolecular radical addition of the 4β-alkoxyl radicals with accompanying formation of the two formates or the corresponding acetates identical with those obtained from the 4α-series. Thus, unlike the corresponding reactions of A-homocholest-4a-en-3-ols and B-homocholest-5-en-7a-ols, the β-scission is a predominant process over the intramolecular radical addition in the alkoxyl radicals derived from A-homocholest-1-en-4α-ols. The paths which led to all the products are discussed on the basis of an ¹⁸O labelling experiment carried out for the formation of 2α-iodomethyl-A-nor-5α-cholestan-1α-ol formate from A-homo-5α-cholest-1-en-4α-ol.