Tertiary Carbinamine Synthesis by Rhodium-Catalyzed [3+2] Annulation of N-Unsubstituted Aromatic Ketimines and Alkynes

A convenient and waste-free synthesis of indene-based tertiary carbinamines by rhodium-catalyzed imine/alkyne [3+2] annulation is described. Under the optimized conditions of 0.5-2.5 mol % [{(cod)Rh(OH)}(2)] (cod = 1,5-cyclooctadiene) catalyst, 1,3-bis(diphenylphosphanyl)propane (DPPP) ligand, in toluene at 120 degrees C, N-unsubstituted aromatic ketimines and internal alkynes were coupled in a 1:1 ratio to form tertiary 1H/-inden-1-amines in good yields and with high selectivities over isoquinoline products. A plausible catalytic cycle involves sequential imine-directed aromatic C H bond activation, alkyne insertion, and a rare example of intramolecular ketimine insertion into a Rh-I-alkenyl linkage.