1,3-Dipolar [3 + 2] Cycloaddition of <i>N</i>-α-Diphenyl Nitrone to the Benzene Ligand in Reductively Activated [Mn(CO)₃(η⁴-C₆H₆)]^-

We have established that the η4-benzene ligand in [Mn(CO)3(η4-C6H6)]- undergoes a stepwise cycloaddition reaction with N-α-diphenyl nitrone in a sequence in which the Lewis acid BF3 is first used to induce nucleophilic addition of [Mn(CO)3(η4-C6H6)]- to N-α-diphenyl nitrone. The BF3 can be removed by protonation to give the neutral intermediate [Mn(CO)3{η5-C6H6CHPhN(Ph)OH}], which can be cyclized by addition of excess KH and PPNCl to drive ring closure and form containing an isoxazolidine ligand that is the [3 + 2] cycloaddition product of the nitrone with benzene.