Rh(III)‐Catalyzed [3+2] Annulation and C−H Alkenylation of Indoles with 1,3‐Diynes by C−H Activation

Abstract

Described herein is the Rh(III)-catalyzed [3 + 2] annulations and C2-alkenylations of indoles with 1,3-diynes, which deliver the synthetically important 3H-pyrrolo[1,2-a]indol-3-ones and highly functionalized tetrasubstituted olefin derivatives. Importantly, in this methodology, the additive controlled selective formation of desired scaffolds. This synthetic strategy exhibits high efficiency and broad functional group compatibility. Furthermore, this protocol has been successfully extended to the synthesis of bisannulated and trisubstituted alkenes. The method is also smoothly applied for the synthesis of the core structure of protein kinase C inhibitor and melatonin analogues.

Recent Advances in the Synthesis of 5‐MemberedN‐Heterocycles via Rhodium Catalysed Cascade Reactions

“…Rh(III)-catalyzed [3 + 2] annulation and CÀ H alkenylation of Indoles with 1,3-diynes by CÀ H activation. [70] and acceptor diazo compounds are used for these reaction as simple diazoacetates or diazoketones failed to work. To overcome these limitations, Sulfur ylides employed as surrogates of diazo compounds in metal-catalyzed reactions owing to its relatively higher security and stability.…”

“…Herein, a Rh(III)-catalyzed additive-controlled [3 + 2] ). [70] Indole and its derivatives especially 2-arylindole, 1-aminoindole etc. are highly privileged heterocyclic moieties widely exists in biologically active molecules, pharmacological compounds and drug molecules.…”

“…Alternatively, cleavage of indole C−N bond ( path‐a ) and consequent protonolysis afforded the indole C2‐alkenylated product 116 , which further undergoes intramolecular cyclization delivered [3+2] annulation product 115 (Scheme 32). [70] …”

“… Rh(III)‐catalyzed [3+2] annulation and C−H alkenylation of Indoles with 1,3‐diynes by C−H activation [70] …”

Rh(III)-Catalyzed Divergent Synthesis of Alkynylated Imidazo[1,5-a]indoles and α,α-Difluoromethylene Tetrasubstituted Alkenes

“…In particular, the C–H annulations of N -carbamoyl indoles with alkynes, a common and versatile coupling partner in C–H activations, have contributed significantly to the synthesis of indole-fused polyheterocycles. The reported C–H annulation reactions between N -carbamoyl indoles and alkynes could be classified into two categories: (i) [4 + 2] annulation for the synthesis of pyrimido­[1,6- a ]­indol-1­(2 H )-ones via Rh catalysis (Scheme a); (ii) [3 + 2] annulation for the synthesis of 3 H -pyrrolo­[1,2- a ]­indol-3-ones via Co, Ru, Re, and Rh catalysis (Scheme b). Despite the remarkable achievements made, however, to the best of our knowledge, the [4 + 1] annulation between N -carbamoyl indoles and alkynes for the synthesis of imidazo­[1,5- a ]­indoles has never been reported to date.…”