| Summary: | It has been established that an electron-deficient cationic Cp<sup>E</sup>-rhodium(III) complex catalyzes the non-oxidative [2+2+2] annulation of <i>N</i>-(1-naphthyl)acetamide with two alkynoates via cleavage of the adjacent C⁻H and C⁻N bonds to give densely substituted phenanthrenes under mild conditions (at 40 °C under air). In this reaction, a dearomatized spiro compound was isolated, which may support the formation of a cationic spiro rhodacycle intermediate in the catalytic cycle. The use of <i>N</i>-(1-naphthyl)acetamide in place of acetanilide switched the reaction pathway from the oxidative [2+2+2] annulation-lactamization via C⁻H/C⁻H cleavage to the non-oxidative [2+2+2] annulation via C⁻H/C⁻N cleavage. This chemoselectivity switch may arise from stabilization of the carbocation in the above cationic spiro rhodacycle by the neighboring phenyl and acetylamino groups, resulting in the nucleophilic C⁻C bond formation followed by β-nitrogen elimination.
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