A convenient quaternization/rearrangement procedure for conversion of thiazoles to medium- and large-sized N,S-heterocycles

Article abstract of DOI:10.1021/jo00113a044

A straightforward, two-step sequence capable of converting simple thiazoles into different sets of ring-expanded N,S-heterocycles of various sizes has been developed. The initial quaternizations of the heterocyclic moieties conducted with α,ω-dihaloalkanes (chain lengths from 2 to 8) in a 1:5 stoichiometry, afford the monoquaternary intermediates in isolated yields ranging from 16-71% (benzothiazole series, 9) to 17-93% (thiazole series, 10), respectively. In the subsequent OH^--induced rearrangement, an expeditious ring-opening/ring-closure event incorporates the previously attached alkyl side chain in the newly formed hetero ring. Here the yields of benzannelated products 11 lie in the interval from 39 to 82%, while the monocyclic counterparts 12 fall within 11 to 59%, which in an overall perspective makes this methodology preparatively significant for an array of new compounds up to (at least) 12-membered ring sizes.