Chemistry of 4-chloro-5-cyano-1,2,3-dithiazolium chloride

The title compound 2, modelled on Appel salt 1, reacts as rapidly as 1 with phenols and anilines; since it lacks a good leaving group at the highly electrophilic C-5 position there is not one low energy reaction pathway, as there is with 1, and the reactions are complex giving more products in lower yields. With phenols it gives 2-aminobenzofuran-3-carbonitriles 3 resulting from initial nucleophilic attack through the phenolic ortho-carbon (Scheme 1). Aniline reacts with 2 largely through nitrogen to give 2-phenyliminopropanedinitrile 7 and the amidine 8, the bis-anilinomalononitrile 9 and the thioamide 10, all derived from 7 (Scheme 2). 1,4-Diaminobenzene reacts similarly with 2 to give the mono- and bis-dicyanoimines 22 and 23, whilst 1,2-diaminobenzene gives the cyclised product 2-aminoquinoxaline-3-carbonitrile 20. 1,8-Diaminonaphthalene gives the sulfur abstraction product, thiadiazine 24, and the quinomethane imine 25 and products derived from it (Scheme 7), in keeping with the high reactivity of the naphthalene ring towards electrophilic substitution. In all of these reactions with aromatic amines, salt 2 is acting as an equivalent of NC–C++–CN (umpolung of malononitrile) whilst with phenols it acts as an equivalent of dicyanocarbene, NC–‥–CN.