13,14-seco-steroids: A new type of modified steroids containing a nine-membered ring

Oxidations of 14 alpha-hydroxy-5 alpha-cholestan-3 beta-yl acetate (5) with lead tetraacetate under thermal or photolytic conditions or in the presence of iodine proceed mainly by fragmentation of the C(13)-C(14) bond to give as the primary products the 13,18-didehydro-13,14-seco derivative 6 and the (E)-Delta(12)-13,14-seco ketone 11, respectively. Further transformations of these compounds under conditions of their formation afforded, in addition, the acetoxy derivatives 7-9 (from 6), and the D-homo-C-nor compound 12 and (12R,13R)-epoxide 13 (from 11). Unexpectedly, the photolytic lead-tetraacetate oxidation of 5 resulted partly (to ca. 20%) in a reversible fragmentation involving scission and recombination of the C(8)-C(14) bond followed by formation of rite 14 beta,22-ether 10. Possible mechanisms for the observed transformations are discussed.