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Thermolysis of Acylazo O-Trimethylsilyl Cyanohydrins:  Azoalkanes Yielding Captodatively Substituted Radicals

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journal contribution
posted on 04.12.1998, 00:00 by Charles F. Billera, Travis B. Dunn, David A. Barry, Paul S. Engel
A new synthetic method has been developed for preparing azoalkanes bearing geminal α-cyano and α-trimethylsiloxy groups. While the symmetrical compound 5 decomposes near room temperature to afford, almost entirely, the C−C dimers, the unsymmetrical azoalkane 3 requires heating to 75 °C. The thermolysis activation parameters of 3 and 5 can be rationalized on steric grounds without invoking captodative radical stabilization. A 13C NMR product study of photolyzed 3 in the presence of TEMPO at 21 °C shows that the fate of caged [tert-butyl, 1-trimethylsiloxy-1-cyanoethyl (14)] radical pairs is disproportionation, 17%, cage recombination, 20%, and cage escape, 63%.