Cyanoketenes. Mechanism of tert-Butylcyanoketene Cycloaddition to Aldo- and Ketoketenes

Article abstract of DOI:10.1021/jo01310a042

tert-Butylcyanoketene cycloadds to ketene, methylketene, dimethylketene, and ethylmethyketene.The first two examples give 2-oxetanones and the last two result in cyclobutane-1,3-diones.These cycloadditions are shown to proceed by a nonconcerted dipolar mechanism involving zwitterionic intermediates.Establishment of the intermediacy of the zwitterions was accomplished by their independent generation from the thermolysis of substituted 4-azido-5-tert-butylcyclopentene-1,3-dione precursors.The mechanistic consequences of these cycloadditions and how they may apply to other ketene dimerizations are discussed.