The preparation of functionalized 1,2-dithiole-3-ylidene thiones 8 via a ring-opening–closing transformation of selected 4-oxothiazolidine enaminoketones 7

March 04, 2024

• Title:       

  The preparation of functionalized 1,2-dithiole-3-ylidene thiones 8 via a ring-opening–closing transformation of selected 4-oxothiazolidine enaminoketones 7

• Image Source:

  Regioselective synthesis of 1,3-thiazines by sequential 4-oxothiazolidine to 1,2-dithiole to 1,3-thiazine transformations: role of intramolecular non-bonded S···O interactions

• Mark:

  Scheme 1

• Associated context:

  The most important structural feature of the compounds,  exhibiting the 1,5-type S···S, S···O or Sb···N interactions,  is a much shorter distance between the corresponding atoms  than the sum of their van der Waals radii (3.60 A, 3.32 A, and 3.74 A, respectively). Over the last few years we have  reported that push–pull 2-alkylidene-4-oxothiazolidines of the general structure 7 (Scheme 1), containing the cisconfigured -S-C=C-C=O moiety, participate in a number of reactions through activation of (i) the nucleophilic α-carbon atom of the exocyclic C=C bond, or (ii) C(4) and  C(5) positions of the heterocyclic ring via activated vinylogous N-methyliminium ions. In particular, we anticipated  that the 1,5-type S/O close contact, in combination with  the rigid and flat 4-oxothiazolidine ring conjugated with  the C(2) side chain, can be electronically tuned to induce  specific chemical transformation of substrates 7. As reported  in a preliminary communication, this has been confirmed experimentally by a ring-opening–closing transformation of selected 4-oxothiazolidine enaminoketones 7 in the presence of Lawesson’s reagent (LR), to produce functionalized 1,2-dithiole-3-ylidene thiones 8 (Scheme 1).