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

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