1.2- Dithiole-3-thiones ring transformations

A ring transformation takes place in the reaction of 3-mercapto- or 3-acylthio-3-isothiazo-line-5-thiones (331) with reactive alkynic compounds in boiling acetonitrile this reaction produces the 1,3-dithiole derivatives (332) in good yields (80JCS(P1)2693, 80H(14)785). 

In all the reactions discussed in this section, both isopropyl groups were transformed into a 1,2-dithiole ring. When N-alkyldiisopropylamines and sulfur monochloride were mixed in chloroform in the absence of another base, that is, DABCO, two monocyclic dithiole-3-thiones 93 and 94 were isolated. 5-Mercapto derivative 93 was the main product in all the cases examined (2001MC165, 2006RCB143 Scheme 45). 

It has been found that a cycloaddition of compound 305 with DMAD affords exclusively spirane 307, which includes a 1,3-dithiole ring (Scheme 57). The expected [3-1-2] cycloaddition as a first phase giving rise to an intermediate 306, followed by a ring closure, rationalizes the reaction outcome. In comparison to 305, a broad range of I,2-dithiole-3-thiones can be efficiently converted into corresponding 2-(2-thioxoalkylidene)-l,3-dithioles, as exemplified by the reaction of 308 with DMAD. Depending on the reaction conditions and structural properties of the initially formed cycloadduct, such as 309, further transformations ate possible. 

Transformations I.4.I.2.I. By Ring Contraction Formation of l,2-Dithiole-3-thiones... 

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