Consecutive Stille-coupling-hydrosilylation-Diels-Alder reaction of 17-iodo-5 alpha-androst-16-ene

Homogeneous catalytic hydrosilylation of pregn-16-en-20-yne (produced from 17-iodo-5 alpha -androst-16-ene by Stille-coupling) with triethylsilane is investigated in the presence of various Pt, Pd and Ph complexes. The stereo selective Diels-Alder reaction of one of the main products (21 -triethylsil yl-pregna- 16,20-diene, 3b) led to a new pentacyclic steroidal derivative. The other steroidal diene (20-triethylsilyl-pregna- 16,20-diene, 3a) underg oes cycloaddition only in the presence of a hydrosilylation catalyst, givin g the same cyclization product. The catalytic isomerization of 3a and 3b as precondition for cycloaddition was supposed. (C) 2001 Elsevier Science B.V . All rights reserved.