5(4H)-oxazolones. Part VIII. An efficient synthesis of Δ1-pyrroline-2-carboxylic acid derivatives through Michael and Wittig condensation

Reaction of oxazolones 4 with triphenylvinylphosphonium bromide 3 afforded, through a Michael addition, the α-aminoesters 7 or acids 8 functionalized with a triphenylphosphonium group. Compounds 7 and 8 were transformed in good yields in the corresponding Δ1-pyrroline-2-carboxylic acids 2 or esters 1 by intramolecular Wittig condensation in presence of sodium alkoxide in refluxing toluene. Intermolecular Wittig reaction of 7 with 4-nitrobenzaldehyde afforded protected unsaturated α-aminoesters 9.