Substituted, Fused, Tricyclic 6,7-Dihydro-1H,5H-pyrido[1,2,3-de]quinoxaline-3-amines by Isocyanide-Abetted Cycloaddition Reaction

A new method for the synthesis of substituted, fused, tricyclic 6,7-dihydro-1H,5H-pyrido[1,2,3-de]quinoxaline-3-amine derivatives from aldehydes, isocyanides, and 1,2,3,4-tetrahydroquinolin-8-amine in the presence of scandium(III) trifluoromethanesulfonate as the catalyst was developed. An inventive approach for the activation of the nitrilium ion with an in situ formed 4-(dimethylamino)pyridine-stabilized imine synthon was also explored to enhance the yield of the desired, fused, tricyclic systems.

6,7-Dihydro-1H,5H-pyrido[1,2,3-de]quinoxaline-3-amine derivatives are prepared from aldehydes, isocyanides, and 1,2,3,4-tetrahydroquinolin-8-amine with scandium(III) trifluoromethanesulfonate [Sc(OTf)₃] as the catalyst. The undesired formation of the Schiff base was solved by activation of the nitrilium ion with an in situ formed 4-(dimethylamino)pyridine (DMAP)-stabilized imine synthon.

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