Novel enantioselective synthesis of trans-α-(2-carboxycycloprop-1-yl)glycines: conformationally constrained l-glutamate analogues

d - and l -α-(2-carboxycycloprop-1-yl)glycines were synthesized from trans -1,3-di(2-furyl)propenone. Conversion of the double bond to a cyclopropane is followed by the formation of an oxime ether. Enantioselective reduction of the oxime ether, separation of diastereomers and oxidation of the furane rings gave enantiomerically pure d - and l -CCG I and CCG II. The structure of oxime 7b was determined by X-ray crystal structure analysis. The key step is the oxazaborolidine catalyzed enantioselective conversion of oxime ethers to amines.