Methyl 2-methyldithiocarbazate in heterocyclic synthesis: preparation of 2,5-disubstituted 1,3,4-thiadiazoles, bis(1,3,4-thiadiazolium) salts and macrocycles containing 1,3,4-thiadiazole subunits. X-Ray crystal structure of 2,2′-bis[4,5-dihydro-5-(2-hydroxyethylimino)-4-methyl-1,3,4-thiadiazole]

Abstract

Reaction of the iminophosphorane 2, derived from methyl 2-methyldithiocarbazate and triphenylphosphine, with carbon disulphide gives the mesoionic compound 3, which reacts with α,ω-dihalogeno compounds to give bis-(1,3,4-thiadiazolines)7–9. However, reaction with ethylenediamine or 1,4-tetramethylenediamine leads to macrocycles 11 and 12. Methyl 2-methyldithiocarbazate, by sequential treatment with dicarboxylic acid chlorides and perchloric acid, leads to the bis-(1,3,4-thiadiazolium) salts 19–21, which undergo nucleophilic displacement of the methylthio group, upon reaction with β-substituted ethylamines, to give products 22–28. The crystal structure of compound 22 has been determined by X-ray crystallography. The crystal could be described in a P1 cell, with parameters a= 11.286 2(17), b= 7.740 9(8), c= 4.267 6(2)Å, α= 93.441(5), β= 91.703(6) and γ= 108.780(12)°. The molecule presents an internal crystallographic inversion centre, and the terminal OH groups are disordered between two tetrahedral positions of the bonded carbon atom.