TM reaction of pheayl isolhiocyanalc with Ihe Knovamgcl Ce active m&ylcne compounds lad gave the non-isolable salts3.a.d. The lauex unduwent in-situ hetcmcyclization on vestment with some halogenatcd compounds e.g. phcnacyl bromide. ethyl bremeacetate. g-bromoacctoacetanilide, ethyl %-bromoacetoacctatc and g -bnxno-Box*butyronitiilc into chc corresponding polyfunctionally substituti 3-(~hii-2'-ylicnelpyridine derivatives. which could also he annulated into fused bctcmcyclic ring systems. Chemical and spectroscopic evidences for Ihc structure of ti new compounds are de.scrihed.
Previously, we have investigated the reaction of isothiocyanatcs with active methylenes followed by hcterocyclization of the resulted adducts with a-halogenated compounds. Such synthetic route proved to be an easy, facile and sole approach for the synthesis of hitherto unreported derivatives of polyfunctionally substituted thiophenes, 2,3-dihydrothiazoles and thiazolidines.ls6 The importance of such derivatives is due to their diverse biological and physiological potentialities as they are known to exhibit nematocidak7 antiprotozoal,* bacterici-da19 and hypoglycemic activity. lo As an extension of such synthetic route, we wish to report herein on the scope and applicability of the Knovenagel condensated products la-d, prepared by us.1 1 for their heterocyclization with some a-halogenated compounds. The work has resulted in the formation of several new polyfunctionally substituted 3-(thiazol-2'-ylidene)pyridines. The latter could also be annulated into fused heterocyclic ring systems of expected wide spectrum of biological activities.
Thus, the base-promoted nucleophilic addition of the acidic Knovenagel condensated candidates la-d to equimolecular amounts of phenyl isothiocyanate in dry dimethylformamide at room temperature afforded the non-isolable potassium sulphide salts 3a-d. In-situ heterocyclization of the latter with phenacyl bromide yielded