Thiadiazoles and thiadiazolines. Part 1. Reaction of thiourea and ethylenethiourea with chlorodiazabutadienes: a new route to 4-amidino-1,3,4-thiadiazolines

Abstract

1-Chloro-1,4-diaryldiazabutadienes (1) react with thiourea to give hydrochlorides of 4-amidino-2,5-diaryl-Δ²-1,3,4-thiadiazolines from which the corresponding free bases (2) are obtained by treatment with cold alkali. Imidazolidine-2-thione (ethylenethiourea) reacts similarly with the chlorodiazabutadienes (1a,b) to give, after treatment with cold alkali, 4-(4,5-dihydroimidazolin-2-yl)-2,5-diaryl-Δ²-1,3,4-thiadiazolines (6a,b). In the presence of an excess of sodium borohydride the reaction of (1a) with thiourea yielded some N²-benzylthiobenzoylhydrazine (12), compatible with the capture of an intermediate iminium ion. A mechanism is suggested for these reactions.