The Barton reaction: can a more tenable pathway be hypothesized for the formation of nitrosoalkyl derivatives?
Herein, we report that in the formation of nitrosoalkyl derivatives during the photolysis of alkyl nitrites, the formation of the intermediate alkyl alkoxy nitroxide, due to the trapping of alkyl radicals by the starting nitrite, is the key step of the entire process. In fact, these nitroxides, detectable by EPR spectroscopy, decay to the final nitroso derivatives under thermodynamic control. In light of this, the Barton reaction mechanism has been reviewed. The nitrosoalkyl derivatives, or the hydroxamic acids when steroids are involved, have now to be considered as the ending products of the entire process and not, unless a very high concentration of NO is present in the medium, the result of a direct reaction of NO with the alkyl radical, as is commonly accepted.
Dipartimento di Chimica Organica A. Mangini, Viale Risorgimento 4, 40136 Bologna, Italy. grossi@ms.fci.unibo.it
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Grossi