A Facile Synthesis of Substituted 1,4-Benzothiazepin-5(4H)-ones and Pyrido[3,2-f][1,4]thiazepin-5(4H)-ones − Crystal and Molecular Structure of 2-Ethylthio-4-methyl-5(4H)-oxopyrido[3,2-f][1,4]thiazepine-3-carbonitrile

A new synthesis of pyrido[3,2-f][1,4]thiazepine derivatives 3 starting with 2-chloronicotinic acid (1), methylaminoacetonitrile hydrochloride and carbon disulfide is described. As proved by a crystal structure determination, a boat conformation with approximated mirror symmetry can be assigned to the 1,4-thiazepine ring in 3b. 2-Chloro-N-cyanomethyl-N-methyl-5-nitrobenzamide (5) reacts with carbon disulfide in presence of a strong base in DMF or DMSO depending on the temperature to either the benzothiopyran compound 6 or by intramolecular aromatic nucleophilic substitution to a seven-membered ring system as thiolate anion which can be alkylated to give the 1,4-benzothiazepine derivative 7, or to an open-chain amido ketene dithioacetal 8.