Halo-Induced Heteroannulation Route to Quinolines

Significance

The cyclization of alkynes containing proximal nucleophilic centers promoted by electrophiles is achieving the status of a general route for carbo- and heterocycle construction. The present is a detailed report of the original study (X. Zhang, M. A. Campo, T. Yao, R. C. Larock Org. Lett. 2005, 7, 763). ICl was shown to effect more efficient cyclizations than I₂ (without a metal catalyst), although Hg(OTf)₂ also gave good yields of products, albeit without the iodo functionality for potential further manipulation. The reaction afforded mixtures of products when R^¹,4,6 is a meta substituent, very poor yields when R^²,³,8 = alkyl, TMS or H, and a failure when EX = NBS.