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,10-octahydroacridine derivatives 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 (3+4-->6). Both absolute configuration and preferred conformation were assigned by detailed NMR studies.