Direct observation and retro-ene reaction of a propargylic diazene. Stereochemical assignment of monoalkyl diazenes

Allylic and propargylic diazenes and their rearrangement by [3,3]-sigmatropic elimination of dinitrogen (retro-enc reaction) have been invoked in numerous organic transformations. As rearrangement uniformly occurs under the conditions of diazene formation, these hypothetical intermediates have not previously been observed, and fundamental questions regarding their stereochemistry (E vs Z) and reactivity remain. Employing a new method for diazene generation, we have been able to produce and study such an intermediate at low temperature and thereby address these issues of structure and mechanism, as described below.