A highly diastereoselective approach to conformationally constrained serine analogues: synthesis of an alpha-amino-beta-hydroxycyclohexenecarboxylic acid and derivatives

A diastereospecific synthesis of alpha-amino-beta-hydroxycyclohexenecarboxylic acid was performed starting from 4-chloromethylene-5(4H)-oxazolone (1), which reacted with 2,3-dimethylbutadiene in the presence of EtAlCl2. The Diels-Alder reaction yielded two diastereosiomeric cycloadducts, depending on the configuration of the starting dienophile 1. By employing other diene reactants, the synthetic process appears to be of general scope for the preparation of carbocyclic serine analogues with controlled substitution of the ring.