Synthesis of 11‐Oxaestrogens via Dye‐Sensitized Photo‐oxygenation of a 9,11‐Didehydroestrone Derivative

The 3‐methoxy‐1 1‐oxaestrone (13) has been synthetized from estrone (3) following an approach that involves the ring‐C fragmentation of the estrogenic skeleton by dye‐sensitized photo‐oxygenation of the properly C(17)‐protected 9,11‐didehydroestrone derivative 6 as the key step. The C(13)‐side‐chain degradation of the 9‐oxo‐9,11‐seco‐aldehyde 7 followed by reduction to the 9β, 12‐diol 10 and further cyclization yields the 11‐oxaestrogenic skeleton. By this procedure, 13 is obtained in 9 steps from 3 with a non‐optimized overall yield of ca. 15%.