Condensation of (2-Bromo-1-phenylethylidene)malononitrile with Substituted Thioureas: An Unusual Ring Size Effect

Article abstract of DOI:10.1021/jo00302a048

Condensations of the title electrophile with ambient S,N-nucleophiles, e.g., thiourea, N,N'-diphenylthiourea, and thiosemicarbazide, proceed via initial S-alkylation followed by closure of the thiazole ring.In contrast to this, cyclic thioureas with the five-, six- and seven-membered rings afford distinct condensation products depending on the size of the ring. 2-Imidazolinethione gave 7-cyano-2,3-dihydro-5-mercapto-6-phenyl-1H-pyrrolo<1,2-a>-imidazole in low yield. 3,4,5,6-Tetrahydro-2(1H)-pyrimidinethione afforded <2-(1-isothiocyano-3-aminopropyl)-1-phenylethylidene>malonitrile in high yield, while 1,3,4,5,6,7-hexahydro-2H-1,3-diazepine-2-thione gave 7-amino-8-cyano-9-phenyl-2,3,4,5-tetrahydropyrido<1,2-a><1,3>diazepine in moderate yield.A common feature of these cyclizations is the primary S-nucleophilic attack, which was confirmed by isolation and characterization of the corresponding intermediates.The effects of ring size are discussed.