Reversible 1,3‐dipolar cycloaddition of dimethyl 2‐thiono‐1,3‐dithiole‐4,5‐dicarboxylate with dimethyl acetylenedicarboxylate

It was shown that dimethyl 2‐thiono‐1,3‐dithiole‐4,5‐dicarboxylate ( 2 ) and dimethyl acetylenedicarboxylate (DMAD) undergo a 1,3‐dipolar cycloaddition to produce a short‐lived ylide intermediate ( 3 ). The 1,3‐dipolar cycloaddition took place even at room temperature, although sluggishly, but took place much more rapidly under application of a high pressure of 500 MPa. The 1,3‐dipolar cycloaddition is reversible and the ylide 3 immediately splits into 2 and DMAD. When the reaction of 2 with DMAD was carried out at room temperature without solvent, a spiro‐1,3‐dithiole ( 11 ) was formed in 11% yield, whereas the reaction at 150°C provided a thiophene derivative ( 13 ) in 41% yield. It was found that 11 undergoes a thermal rearrangement to 13 . Results of attempted chemical trapping of the ylide 3 are also reported. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:434–440, 2000     

Reactions of benzeneselenyl and benzenesulfenyl chlorides with syn‐ and anti‐9,9′‐bibenzonorbornenylidenes

Reaction of syn‐9,9′‐bibenzonorbornenylidene (1a) with benzeneselenyl chloride produced vic‐dichloride (4) exclusively, which corresponds to the cis‐addition product of 1a with molecular chlorine, with retention of the original alkene configuration. Moreover, the reaction of anti‐9,9′‐bibenzonorbornenylidene (1b) with benzeneselenyl chloride gave the same vic‐dichloride (4) exclusively with inversion of the original alkene configuration. No expected benzeneselenyl chloride adducts were formed in both cases. On the other hand, reactions of 1a and 1b with benzenesulfenyl chloride only resulted in the syn–anti isomerization of the alkenes without any adduct formation. Mechanisms of these reactions are discussed in some detail. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:625–629, 2001