Selective N, O-Addition of the TEMPO Radical to Conjugated Boryldienes

B(C6F5)(2)-containing boryldienes 4 underwent the addition of two molar equivalents of TEMPO to give N, O-bonded four-membered heterocyclic products 7. The reaction is a metal-free example of the generation of reactive nitrogen-centered TEMPO radical derivatives, in this case by the addition of TEMPO to the borane, followed by carbon-nitrogen bond formation and subsequent trapping of the resulting allyl radical by the second equivalent of TEMPO.