LEWIS-ACID CATALYZED TRANS-ALLYLSILYLATION OF UNACTIVATED ALKYNES

The addition of different substituted allylsilanes 2 to unactivated al kynes 1 in the presence of catalytic amounts of HfCl4 or the EtAlCl2-T MSCl catalyst system produced in high yields the silylated 1,4-dienes 3 regio- and stereoselectively. The exclusive trans manner of addition was confirmed by analysis of crude reaction mixtures by H-1 NMR and c apillary GLC methods. Good agreement of relative reactivities of react ion of various allylsilanes 2a-e toward phenylacetylene (la) in the pr esence of HfCl4 with the relative reaction rates of 2a-e with carbeniu m ions supported the involvement of cationic species 11 as a reaction intermediate. The mechanisms for the HfCl4 and EtAlCl2-TMS catalyzed t rans-allylsilylation of alkynes are proposed.