Furoxans, computational studies

The rearrangement of 2-phenyl-3-butyn-2-ol to 3-phenybut-2-en-l-al was examined computationally. The carbocation PhMeC+-C=CH is considered an intermediate or, under some conditions, a transition state. The stepwise Diels-Alder reaction of 1-trimethylsiloxy-1,3-butadiene and 4,6-dinitrobenzofuroxan was studied by computational methods. A stepwise mechanism with a persistent intermediate is supported. However, this intermediate is suggested to be a heterocyclic adduct and not the zwitterionic allyl cation/furoxan anion adduct proposed in the previous studies. 

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