Quantum Chemical Study of the Mechanism of a New Heterocyclization of Bis(2‐Chloroprop‐2‐Enyl) Sulfide in Alkali/Hydrazine Hydrate Medium
Nikita V. Teplyashin, Alexander S. Bobkov, Nadezhda M. Vitkovskaya, Alexey R. Romanov, Nikolai A. Korchevin, Igor B. RozentsveigABSTRACT
The paper reports a new example of the heterocyclization of bis(2‐chloroprop‐2‐enyl) sulfide to 1‐(3‐methyl‐5‐methylenedihydrothiophen‐2(3 H )‐ylidene)‐2‐(propan‐2‐ylidene) hydrazine in a KOH/N 2 H 4 ·H 2 O medium. The product was obtained in 25% yield after 4 h at 50°C in the presence of a fourfold excess of alkali. A mechanism for its formation was proposed and theoretically substantiated using quantum chemical methods (B2PLYP‐D2/6‐311+G**//B3LYP/6‐31+G* + IEF PCM (B3LYP/6‐31+G*)). The proposed mechanism involves dehydrochlorination of bis(2‐chloroprop‐2‐enyl) sulfide, hydrazination of allenylpropynyl sulfide, reduction of propen‐2‐yldiazene, reaction of acetone hydrazonide with bis(2‐chloroprop‐2‐enyl) sulfide, prototropic rearrangements to allenyl‐2‐(propan‐2‐ylidene) hydrazine, generation of methylidenethiirane, and formation of the thiolane cycle. In particular, propen‐2‐yldiazene was shown to be reduced in alkaline medium by a diimine molecule formed from hydrazine and atmospheric oxygen.