R-amino, and R-thioalkoxy esters in generally good yield with a complete retention of the stereochemistry of the double bond of the diazo precursor. An extension of the process in homochiral series has also been devised using either a chiral auxiliary attached to the ester function or achiral R-vinyldiazoesters and Doyle's chiral catalyst Rh 2 (MEPY) 4 . In the former approach, pantolactone as chiral auxiliary gave diastereoselectivities of up to 70%, while the second approach produced the desired allylsilane with ee as high as 72%. On the other hand, Rh 2 (MEPY) 4 -catalyzed insertion into the O-H bond of water led to poor or no enantioselectivity in good agreement with recent literature reports. DiscussionSynthesis of (E)-and (Z)-Vinyldiazoesters. Vinyldiazomethanes have been used in various contexts in the

A Stereospecific Access to Allylic Systems Using Rhodium(II)-Vinyl Carbenoid Insertion into Si-H, O-H, and N-H Bonds.-Rhcatalyzed decomposition of α-vinyldiazoesters such as (I) (10 examples) in the presence of silanes, alcohols, amines and thiols produces the corresponding αsilyl, α-hydroxy, α-alkoxy, α-amino, and α-thioalkoxy esters in good yield. The stereochemistry of the double bond in the diazo precursor remains unchanged. Asymmetric application to the synthesis of these allylic synthons is carried out using a chiral auxiliary attached to the ester function or using chiral catalysts. In the latter case enantioselectivities up to 72% are obtained, the best selectivity attained so far in such insertions. -(BULUGAHAPITIYA, P.; LANDAIS, Y.; PARRA-RAPADO, L.; PLANCHENAULT, D.; WEBER, V.; J. Org. Chem. 62 (1997) 6, 1630-1641; Inst. Chim. Org., Coll. Propedeut., Univ. Lausanne, CH-1015 Lausanne-Dorigny, Switz.; EN)