Enantioselective Synthesis of [(1R,3-exo)-2-Benzyl-2-azabicyclo[2.2.1]hept-5-en-3-yl]methanol via Aza-Diels-Alder Reaction

The asymmetric aza-Diels-Alder reaction of the 8-phenylneomenthyl (or 8-phenylisomenthyl) glyoxylate-derived N-benzylimine with cyclopentadiene resulted in the enantioselective synthesis of the corresponding [(1R,3-exo)-2-benzyl-2-azabicy­clo[2.2.1] hept-5-en-3-yl]carboxylate. In both cases, the (1R,3-exo)-adduct was the main diastereomer and was isolated in 70% and 65% yield, respectively. Reduction of the (1R,3-exo)-adducts with LiAlH4 afforded [(1R,3-exo)-2-benzyl-2-azabicyclo[2.2.1] hept-5-en-3-yl]methanol, with recovery of the chiral auxiliaries with retention of configuration.