Formation of cyclopropa[c]indole system in the Mn-mediated radical addition of cyclohexane-1,3-diones to N-substituted acrylamides

Manganese(III) acetate-mediated radical cyclization of N-substituted acrylamides with cyclohexane-1,3-diones gives 4-oxo-2,3,4,5,6,7-hexahydrobenzofuran-2-carboxamides and unexpected tricyclic 1,1a,5,6-tetrahydro-2H-cyclopropa[c]indole-2,7(3H)-diones. The structure of one representative tricyclic compound was confirmed by X-ray analysis. The reaction mechanism was examined employing some structural analogues of the reactants.