Cp∗Rh(III)-Catalyzed Cross-Coupling of Alkyltrifluoroborate with α-Diazomalonates for C(sp³)-C(sp³) Bond Formation

A Cp∗Rh(III)-catalyzed cross-coupling of alkyltrifluoroborate with α-diazomalonates was developed; the C(sp3)-C(sp3) bond coupled products were formed in up to 97% yields. The reaction tolerates some useful functional groups, including ketone, ester, amide, ether, sulfonyl, and thiophene. Electrospray ionization mass spectrometry (ESI-MS) analysis revealed the formation of a distinct molecular species corresponding to σ-alkylrhodium(III) complexes. The successful diazo coupling reaction may be attributed to coordination of the amide group that promotes stability of the alkylrhodium(III) complex through the formation of a five-membered metallacycle.