Multicomponent Reaction for Selective Synthesis of Spiro [indene-2,7′-isoquinoline] and 1,2,8,8 a-Tetrahydroisoquinoline Derivatives

The piperidine promoted three-component reaction of N-alkylpiperidin-4-ones, malononitrile and 2-arylidene-1,3-indanediones in ethanol selectively resulted in the spiro[indene-2,7'-isoquinoline] and the ring-opened cis- or trans-1,2,8,8a-tetrahydroisoquinoline derivatives at room temperature or at the elevated temperature. However, the four-component reaction N-alkylpiperidin-4-ones, malononitrile, aromatic aldehydes and 1,3-indanedione in refluxing ethanol mainly afforded ring-opened cis-1,2,8,8a-tetrahydroisoquinoline derivatives in good yields and with high diastereoselectivity. A plausible domino reaction mechanism was proposed for the formation of the different polycyclic products.