Asymmetric synthesis of 2-amino-3-hydroxynorbornene-2-carboxylic acid derivatives

The enantioselective synthesis of 2-amino-3-hydroxynorbornene-2-carboxylic acid derivatives (5) was studied using the Diels-Alder reaction between cyc lopentadiene and different dienophiles, i.e., alkyl 5-oxo-2-phenyloxazol-4- methylenecarbonates (1) or 2-benzoylamino-3-alkoxycarbonyloxy-acrylates. (1 2), operating with different Lewis acids and both with thermal and with ult rasound conditions. The enantioselective synthesis of the exo/endo compound s 5c,d and 5 'c,d was achieved starting from the chiral menthyl acrylates 1 2b,c using Mg(ClO4)(2) as the catalyst and ultrasound. The cycloadducts wer e obtained in very good yield, in mild conditions, in short time, and in go od diastereomeric excess (exo, 80%; endo, 87%). Finally, the use of alkylid ene-oxazolones or acrylates and EtAlCl2 or Mg(ClO4)(2) as the catalyst allo wed control of the cycloaddition reaction in favor of the exo or endo produ cts.