sentences:  Lastly, the insertion of the carbonyl group of 3 in the residual carbon-titanium connection forms a cyclopropane ring.In the transition state of this elementary stage, which is the limiting stage of the reaction, an agostic interaction stabilizing between the beta hydrogen and the R2 group and the titanium atom was called upon to explain the diastereoselectivity observed.Complex 4 obtained is a tetraalkyloxytitanium compound able to play a part similar to that of the starting tetraisopropyloxytitanate, which closes the catalytic cycle.