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.
乙醛酸 8-苯基新
戊二烯酯(或 8-苯基
异戊二烯酯)衍生的 N-苄基
亚胺与
环戊二烯的不对称偶氮-Diels-Alder 反应导致了相应的[(1R,3-exo)-2-苄基-
2-氮杂双环[2.2.1]庚-5-烯-3-基]
羧酸对映体选择性合成。在这两种情况下,(1R,3-exo)-加合物是主要的非对映异构体,分别以 70% 和 65% 的收率分离出来。用 LiAlH4 还原(1R,3-exo)-加合物可得到[(1R,3-exo)-2-苄基-
2-氮杂双环[2.2.1]庚-5-烯-3-基]
甲醇,同时回收手性助剂并保留构型。