Intramolecular hetero-Diels-Alder reaction of N-arylimines. Applications to the synthesis of octahydroacridine derivatives

A new intramolecular Lewis acid catalyzed hetero-Diels-Alder reaction of N-arylimines 5 with nonactivated olefins tethered to the 2-azadiene system was developed in order to prepare 1,2,3,4,-4a,9,9a,l0-octahydroacridined erivatives 6. Both reactivity and cis/ trans selectivity of 6 were mainly dependent on the substitution pattern in the 3-position of the cyclization precursor 5. The type of Lewis acid plays only a minor role in determination of the cis/trans ratio. The synthetic utility of this new cyclization was increased by performing it as a one-pot reaction. Both absolute configuration and preferred conformation were assigned by detailed NMR studies.