A Rhodium-Catalyzed C−H Activation/Cycloisomerization Tandem

A reaction cascade comprising a rhodium-catalyzed C−H activation, a subsequent hydrometalation of an alkylidene cyclopropane in vicinity, regioselective C−C bond activation of the flanking cyclopropane ring, followed by reductive elimination of the resulting metallacycle, opens a new entry into functionalized cycloheptene derivatives. This crossover of C−H activation and higher order cycloaddition has been performed in two different formats, either using alkylidenecyclopropanes with a lateral vinylpyridine moiety or with a pending aldehyde group as the trigger. The reaction tolerates various functional groups, leaves chiral centers α to the reacting sites unaffected, and proceeds with excellent stereoselectivity. Labeling experiments support the proposed mechanism explaining the observed net cycloisomerization process.