Oxazoline N-oxide mediated [3+2] cycloadditions:: Application to a formal synthesis of a (+)-β-methylcarbapenem

[3+2] Cycloaddition between a camphor-derived oxazoline N-oxide 9 and the gamma,delta-unsaturated enamino ester 11 afforded the single adduct 6, A stereoselective reduction of the enamine ester side chain allowed the control of the absolute configuration of the two additional asymmetric centres. Nitrogen protection and oxidative hydrolysis of the resulting product 13, followed by further functional group manipulations, led to the p-lactam derivative 1, a known precursor of the beta-methylthienamycin derivative 2a.