A CONVENIENT QUATERNIZATION REARRANGEMENT PROCEDURE FOR CONVERSION OF THIAZOLES TO MEDIUM-SIZED AND LARGE-SIZED N,S-HETEROCYCLES

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 alpha,omega-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.