Herstellung und Reaktionen der valenzpolaromeren Verbindung (4,4‐Dimethyl‐2‐thiazolin‐5‐dimethyliminium)‐2‐thiolat ⇌ (1‐Dimethylthiocarbamoyl‐1‐methyl‐äthyl)‐isothiocyanat aus 3‐Dimethyl‐amino‐2,2‐dimethyl‐2H‐azirin und Schwefelkohlenstoff

Abstract

Synthesis and reactions of the valence polaromeric compound (4,4‐dimethyl‐2‐thiazoline‐5‐dimethyliminium)‐2‐thiolate ⇌ 1‐dimethylthiocarbamoyl‐1‐methyl‐ethyl isothiocyanate from 3‐dimethylamino‐2,2‐dimethyl‐2H‐azirine and carbon disulfide.3‐Dimethylamino‐2,2‐dimethyl‐2H‐azirine (1) reacts with carbon disulfide to give crystals which have the dipolar structure 3a [(4,4‐dimethyl‐2‐thiazoline‐5‐dimethyliminium)‐2‐thiolate, Scheme 1]. In solution, the non‐dipolar (charge‐free) isomeric form 3b (1‐Dimethyl‐thiocarbamoyl‐1‐methyl‐ethyl isothiocyanate) is almost exclusively populated. Reaction products are derived from both forms: Derivatives of 3a are the hydrolysis product 6, the sodium borohydride reduction product 7 and the methylation products 9 and 10, respectively (Scheme 2). The isothiocyanate form 3b is responsible for the various reaction products with amines (Scheme 3). One of the reaction products with ammonia, namely 20, is also obtained by the reaction of 1 with thiocyanic acid.Thermolysis of the azirine/carbon disulfide adduct 3 leads to 2‐dimethylamino‐4,4‐dimethyl‐2‐thiazoline‐5‐thione (17) in high yield. A possible mechanism is outlined in Scheme 4. The same compound is also formed by rearrangement of 3 under the catalytic influence of dimethylamine. Its structure has been established by X‐ray crystallography (section 4). Again a rearrangement is involved in the reductive (NaBH4) conversion of 17 to 7, the direct reduction product of the dipolar species 3a (Scheme 5).The isothiocyanate form 3b is able to react with a second molecule of 3‐dimethylamino‐2,2‐dimethyl‐2H‐azirine (1) to yield compound 25, which in the crystalline or dissolved state appears to be almost entirely populated by the carbodiimide form with structure 25b (Scheme 7), though all reaction products of 25 (reduction with sodium borohydride, addition of water or hydrogen sulfide, Schemes 7 and 8) are derived from the dipolar form 25a, not detectable as such; here again therefore there is a dynamic equilibrium 25a ⇌ 25b.The two forms of adduct 3, namely 3a and 3b, are obviously very easily interconverted at room temperature and therefore can be considered as valence polaromeric forms (section 5). A classification of the dipolar (zwitterionic) form is given, which allows a comparison of various dipolar species and gives as indication of charge stabilization by delocalization.The versatile reactivity of the 3‐dimethylamino‐2,2‐dimethyl‐2H‐azirine/carbon disulfide adduct is demonstrated by the fact that with simple reagents approximately 25 derivatives have been obtained, most of them being new heterocyclic compounds.