Reformatsky reactions with N-arylpyrrolidine-2-thiones: Synthesis of tricyclic analogues of quinolone antibacterial agents

A convenient synthesis of 5-oxo-1,2,3,5-tetrahydropyrrolo[1,2-α]quinoline-4-carboxylic acids, tricylic analogues of the quinolone antibiotics, is described. Key steps in the route are a novel zinc-mediated Reformatsky reaction between diethyl bromomalonate and N-arylpyrrolidine-2-thione 18, and cyclisation of the resulting diethyl pyrrolidinylidenemalonate intermediates 19 in polyphosphoric acid. The products proved to be devoid of biological activity. © 2001 Elsevier Science Ltd. All rights reserved.