Copper-catalyzed cyclization of steroidal acylaminoacetylenes:: Syntheses of novel 11β-aryl-17,17-spiro[(4′H,5′-methylene)oxazol]-substituted steroids

A variety of novel 11 beta-aryl-17,17-spiro[(4'H,5'-methylene)oxazol]-substituted steroids have been synthesized in moderate to good yields via copper-catalyzed cyclization of acylaminoacetylenes. The best result was obtained with a catalytic amount of CuI in 1:1 benzene-Et3N at 90 degrees C for 30 min (Ar = 3,4-difluorophenyl; R = ethyl; 97% yield).