Reaction of the title imines with diphenyldiazomethane gives a Δ3‐1,3,4‐triazoline, which leads, after loss of dinitrogen, to a transient azomethine ylide. Subsequent elimination of ethyl or methyl chloroformate gives the unexpected 1,1‐diphenyl‐4,4‐dichloro‐2‐aza‐1,3‐butadiene.
The reaction of ethyl diazoacetate with the N-ethoxycarbonyl-N-(2,2,2-trichloroethylidene)amine yields, by a nucleophilic addition, a new diazo compound that gives 1,3-dipolar cycloaddition reactions with acetylenic esters and maleimides. With acetylenic esters, the cycloadduct leads to substituted pyrazoles by [1,5] sigmatropic rearrangements. With maleimides, we observe a diastereospecific cycloaddition reaction. The intermediary cycloadduct evolves by nitrogen elimination to give a maleimidocyclopropane. The diastereospecificity was explained by an endo-anti approach of the reactants. Keywords: N-ethoxycarbonyl-N-(2,2,2-trichloroethylidene)amine, ethyl diazoacetate, nucleophilic addition, 1,3-dipolar cycloaddition, sigmatropic rearrangement, diastereoselectivity.
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