The structure of 19R-methoxy-5,19-methyleneoxido-17β-acetoxy-5β-androstan-3-one

C 2 3 0 5 H 3 4 , monoclinic, P21, a= 10.098 (4), b=7.394 (2), c= 15.916 (7) ]k, fl= 116-60 (5) °, Z=2, 0¢,~= 1-221 g cm -a. The compound was the major product from the ultraviolet irradiation of 19,19-dimethoxy-17fl-acetoxy-4-androsten-3-one. Upon irradiation, ring closure occurred between one of the methoxy groups and C(5) with the consequence that the A/B ring junction is cis. In the major product the other methoxy group on C(19) has the R stereoconfiguration, i.e. it is directed over ring B. The crystals studied were twinned unequally, so that the observed data were easily corrected for intensity contributions from the minor twin.