Dithiazole series, cycloadditions

Cycloadditions including a cyclic S atom and an exocyclic C=X bond are known in the dithiazole series, e.g. as shown in Scheme 44. 

Pacquer et al. also recognized a second series of intensely colored 1 1 adducts, the trithiapentalenes 153, from benzyne and 5-aryl-l,2-dithiole-3-thiones (151).93 Although very little of 153 (Ar = Ph) was obtained (< 1%), p-anisyl, p-tolyl, and p-chlorophenyl compounds were formed in higher yields. Unsuccessful attempts to achieve the conversion 152 - 153 render more likely an independent pathway for the formation of 153, e.g., one involving an initial 1,2-cycloaddition of benzyne to the exocyclic C=S bond of 151. Derivatives of the related l,2,4-dithiazole-3-thione system 160 and benzyne also afford two series of 1 1 adducts 161 and 162 corresponding to 152 and 153, respectively.93... 

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