UNUSUAL CYCLIZATION PRODUCTS DERIVED FROM PHOTOLYSIS OF BRESLOW'S STEROIDAL BENZOPHENONE ESTERS

In 1973, Breslow and co-workers developed a method for “remote functionalization” of steroids,2 namely, functionalization of C9, C14, and C17 by photolysis of benzophenone esters R-linked to the steroid backbone at C3. They observed selective abstraction of tertiary hydrogens by the diradical of the benzophenone carbonyl and, by choosing tethers of appropriate length, were able to achieve good regioselectivity of hydrogen atom abstraction, e.g., selectivity for abstraction of C9, C14, or C17. Recently, our efforts have been directed at expanding the Breslow concept to natural product synthesis.3 In a projected total synthesis of xestobergsterol A (1), a potent