Iron-catalysed asymmetric carboazidation of styrenes


Previous studies on azidation reactions in this and other laboratories provided evidence that metal-catalyzed radical azidation often involves intermolecular transfer of an azido group from the metal catalyst to a carbon radical. Such radical group transfer reactions do not involve interactions between metal species and radicals, and accordingly few believed that this type of transformation could be enantioselective. Before we obtained positive results, we were not sure that whether enantioselectivity is possible and we navigated like a boat at night in the middle of the ocean. One of my most intelligent students felt that this task was impossible, and declined to continue to work on the project. Luckily, two other students Liang Ge and Huan Zhou elected to trust me and pursue the project. It was a long trip and many times we almost lost our faith. Research by Professor Joseph Ready from UT Southwestern Medical Center revealing rhodium-catalyzed enantioselective radical addition of CBr4 to olefins encouraged us in this dark time.

We finally achieved positive results, but then the problem became how to convince others that this is truly a group transfer reaction. Many people feel profoundly, that enantioselectivity in metal catalyzed radical reactions indicates instead an inner-sphere, high valent metal pathway.

Fortunately, two excellent chemists, Dr. Mong-Feng Chiou and Professor Xinhao Zhang supported us in a timely fashion and in the light of their work the proposed mechanism appears to be quite convincing.

Submission of our paper was also a long story, too long to relate here. Many people helped us and we truly appreciate the assistance we received from experts, editors and students. It is our hope that readers will like this work and find it useful.


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