REGIO-SELECTIVITY AND DIASTEREO-SELECTIVITY OF THE INSERTION OF ALDEHYDES INTO ALKYNE ZIRCONOCENE COMPLEXES

Insertion of aldehydes into alkyne-zirconocene complexes provides conf igurationally pure allyl alcohols in a one-pot procedure. In the case of unsymmetrical alkynes, the regioselectivity of the insertion proces s is high for terminal alkynes. With trimethylsilyl-substituted alkyne s the regioselectivity is low. The insertion of chiral aldehydes into the symmetrical oct-4-yne-zirconocene complex provides the Cram isomer as the major product. On the other hand, reaction of the complex deri ved from a terminal alkyne with 2-phenylpropanal leads primarily to th e anti-Cram product. The results are explained in terms of a four-cent re transition-state model.