Thermal cyclopropyl-allyl anion transformation

It was only after Woodward and Hoffmann in 1965 had predicted a conrotatory mode for the thermal cyclopropyl-allyl anion transformation that a new interest developed in this reaction. By means of the iso-7c-electronic aziridine 310 Huisgen and coworkers succeeded in demonstrating that the thermal recation gave a conrotatory formation of azomethine ylid (311) and that the light-induced reaction resulted in a disrotation to give 312. 

These results have been attributed to an increased ionicity of the carbon-lithium bond in the case of 331 and 340 as compared to 342 and 343 . This conclusion is supported by electrochemical measurements and MNDO calculations A similar conclusion had been reached earlier by Boche and Martens for thermal cyclopropyl-allyl anion transformations. 

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