Regiocontrolled Coupling of Aromatic and Vinylic Amides with α-Allenols To Form γ-Lactams via Rhodium(III)-Catalyzed C–H Activation

Abstract

A mild, regiocontrolled coupling of aromatic and vinylic amides with α-allenols to form γ-lactams via rhodium(III)-catalyzed C-H activation has been demonstrated. This [4 + 1] annulation reaction provides an efficient method for the synthesis of isoindolinones and 1,5-dihydro-pyrrol-2-ones bearing a tetrasubstituted carbon atom α to the nitrogen atom with good functional group tolerance. The hydroxyl group in the allene substrate is essential in controlling the chemo- and regioselectivity of the reaction probably by coordination interaction with the rhodium catalyst.

Rh(III)-Catalyzed C–H Bond Activation for the Construction of Heterocycles with sp3-Carbon Centers

“…Mechanistic studies demonstrated that C-H activation is turnover-limiting and irreversible, which is similar to the synthesis of some dihydroisoquinolones [70]. After that, other scientists took advantage of ethenesulfonyl fluoride [71], hydrazones from ketones and hydrazins in-situ [72], α-allenols [73], and ketenimines [74] as another coupling partners to synthesize various isoindolinone analogues, respectively. In 2013, Rovis and co-workers developed a new approach to access isoindolinones bearing a quaternary carbon center by using diazo compounds as one-carbon synthons (Scheme 12) [69].…”

Co(III)‐Catalyzed [4+1] Annulation of Amides with Allenes via C−H Activation

“…Thus, the barely soluble Ag 2 O or Ag 2 CO 3 acts as better oxidants, which might neutralize the AcOH produced during the reaction to maintain a low concentration of OAc − in the catalytic solution. It is noteworthy that the reaction in the presence of RhCp* catalyst gave 3 aa in 61% yield (see supporting information), which was unsuccessful in the Lu's reaction conditions …”

“…However, the present reaction failed to afford the desired annulation products with 1,1‐disubstituted and simple aliphatic allenes containing ester, silyl, and hydroxyl group. It is noteworthy that hydroxymethylallene does not undergo annulation with benzamide 1 a , in contrast to the RhCp*‐catalyzed oxidative annulation reaction …”

Rhodium‐Catalyzed Alkenyl C−H Activation and Oxidative Coupling with Allylic Alcohols

“…Allylic alcohols were prepared according to reported procedures . Alkenylpyridines, [Cp*Rh(SbF 6 ) 2 ](MeCN) 3 , [Cp*Rh(OTf) 2 ](MeCN) 3 , 2‐cyclohexenylpyrimidine, 1‐cyclohexenyl‐1 H ‐pyrazole, cyclohexenyl(pyrrolidin‐1‐yl)methanone, and N ‐methoxycyclohex‐1‐enecarboxamide were prepared according to reported procedures. All other chemicals were obtained from commercial vendors and used as received.…”