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 stereoselective Diels-Alder reaction of one of the main products (21 -triethylsilyl-pregna- 16,20-diene, 3b) led to a new pentacyclic steroidal derivative. The other steroidal diene (20-triethylsilyl-pregna- 16,20-diene, 3a) undergoes cycloaddition only in the presence of a hydrosilylation catalyst, giving the same cyclization product. The catalytic isomerization of 3a and 3b as precondition for cycloaddition was supposed.