Investigation of Lewis acid-catalyzed asymmetric aza-Diels-Alder reactions of 2H-azirines

Asymmetric Diels-Alder reactions with 2H-azirines as dienophiles have been studied. Diastereoselective reactions with an enantiopure azirine 1b, bearing a chiral auxiliary, gave substituted bi- and tricyclic tetrahydropyridines in high yield and stereoselectivity, under the influence of a Lewis acid. The novel enantioselective 4+2] cycloaddition reaction of 3-benzyl-2H-azirine carboxylate with cyclopentadiene was investigated with various chiral Lewis acid complexes and provided the corresponding tetrahydropyridines in moderate to low yield and enantioselectivity.