REGIOSPECIFIC RING-OPENING REACTIONS OF AZIRIDINES BEARING AN ALPHA,BETA-UNSATURATED ESTER GROUP WITH TRIFLUOROACETIC-ACID OR METHANESULFONIC-ACID - APPLICATION TO THE STEREOSELECTIVE SYNTHESIS OF (E)-ALKENE DIPEPTIDE ISOSTERES

Reaction of N-(2,4,6-trimethylphenylsulfonyl)-gamma,delta-cis- or -tra ns-gamma,delta-epimino (E)-alpha,beta-enoates with acids such as TFA o r methanesulfonic acid (MSA) affords the stereo- and regioselective ri ng-opened products in high yields, and subsequent treatment of resulti ng delta-aminated gamma-mesyloxy alpha,beta-enoates with organocopper reagents yields diastereoisomerically pure (E)-alkene dipeptide isoste res.