DIASTEREOSELECTIVE 1,3-DIPOLAR CYCLOADDITIONS AND MICHAEL REACTIONS OF AZOMETHINE YLIDES TO )-3-BENZOYL-4-METHYLIDENE-2-PHENYLOXAZOLIDIN-5-ONE AND -3-BENZOYL-2-T-BUTYL-4-METHYLIDENEOXAZOLIDIN-5-ONE

The 1,3-dipolar cycloaddition reactions of (1) and (11) with the azome thine ylides derived from N-benzylidene alpha-amino acid esters (2) pr oceed with good to high exo-diastereoselectivity giving the cycloadduc ts (4) and (12), respectively. The cycloaddition adducts can be conver ted to highly functionalised prolines (14), (15) and (17) in high enan tiomeric purities. The Michael addition adducts of (1) and (11) with t he azomethine ylides derived from the N-(disubstituted methylidene) al pha-amino acid esters (18), (19) and (33) allow for a practical synthe sis of all four stereoisomers of 4-benzamidopyroglutamate. The stereoc hemistry of these cycloaddition and Michael adducts has been extensive ly determined by single-crystal X-ray structural analysis [compounds ( 4b), (5b,d), (12b,d), (13e), (15), (20), (21) and (27)]. Lithium-chela ted transition state structures have been proposed to rationalize the stereochemical outcomes of these reactions.