Catalyst-free ambient temperature synthesis of isoquinoline-fused benzimidazoles from 2-alkynylbenzaldehydes via alkyne hydroamination

An efficient environmentally benign route for the synthesis of benzimidazo[2,1-a]isoquinoline has been developed by reacting 2-ethynylbenzaldehyde and related substituted alkynylbenzaldehydes with variously substituted ortho-phenylenediamines and aliphatic amines in ethanol.