A simple, tandem approach to the construction of pyridine derivatives under metal-free conditions: a one-step synthesis of the monoterpene natural product, (-)-actinidine.

A simple and modular one-step synthesis of diversely substituted pyridines from readily available α,β-unsaturated carbonyl compounds and propargylic amines has been developed. The present protocol has a broad substrate scope and allows access to multi-substituted pyridines with select control of the substitution pattern under mild and metal-free conditions. The reaction involves imine formation followed by concomitant cyclization through an allenyl intermediate to afford pyridines in excellent yields, with water as the sole by-product. This mild strategy is also suitable for functionalization of natural products or other advanced intermediates having α,β-unsaturated carbonyl functionality. The utility of the present protocol was showcased with the synthesis of the monoterpene alkaloid, (-)-actinidine, an ant-associated iridoid.