Abstract
The acrylate derivatives of the (R)-4-(3-hydroxy-4,4-dimethyl-2-oxopyrrolidin-1-yl)benzoic acid benzyl ester (R)-2 reacted with 1-(benzyloxycarbonylamino)cycloheadiene 3 under microwave irradiation in solvent-free conditions to yield [4+2] cycloadducts in good yields (91%). The reaction proceeded with moderate endo selectivity (67%) and good facial selectivity (90%). The major cycloadducts were isolated and transformed to afford three enantiopure bicyclic ß-amino acids (1S,2R,4R)-1-(benzyloxycarbonylamino)bicyclo[2,2]oct-5-ene-2-carboxylic acid [(1S,2R,4R)-4], (1R,2R,4S)-1-[benzyl-oxycarbonylamino)bicyclo[2,2,2]oct-5-ene-2-carboxylic acid [(1R,2R,4S)-5] and (R)-1-aminobicyclo[2,2,2]octane-2-carbocylic acid[(R)-6]. This work has led to the preparation of these enantiopure bicyclic ß-amino acids and provides a rare example of an asymmetric Diels-Alder reaction by microwave activation.