One-Pot Transannulation of N-Sulfonyl-1,2,3-triazoles to Dihydro-β-carbolines and Dihydroisoquinolines via Rhodium-Catalyzed C–H Insertion-cum-Base-Mediated Aza-Michael Reaction

Continuous Flow Synthesis of N-Sulfonyl-1,2,3-triazoles for Tandem Relay Cu/Rh Dual Catalysis

The continuous flow synthesis of N-sulfonyl-1,2,3-triazoles, which are convenient reactive azavinyl carbene precursors, for tandem relay Cu/Rh dual catalysis has been developed. Most reactions readily proceeded at 75 °C in a short residence time of 13.09 min in the presence of 2.5 mol % of CuTC. The scope of the reactions was explored by synthesizing diversely functionalized N-sulfonyl and sulfamoyl triazoles in yields ranging from 92 to 98%. To demonstrate the scalability of the process, the reaction was conducted on a 5.4 mmol scale with residence and collection times of 13.09 and 60 min, respectively. Furthermore, a series of controlled experiments were performed to investigate the compatibility of Cu and Rh in a batch or a continuous flow system. Finally, the first integrated flow system using the azavinyl carbene intermediate under the tandem relay Cu/Rh dual catalysis was developed for the synthesis of various cis-diamino enones from alkynes and sulfonyl azides.

Unearthing the Subtleties of Rhodium(II)-Catalyzed Carbenoid Cycloadditions to Furans with an N-Sulfonyl-1,2,3-triazole Probe

The rhodium(II)-catalyzed reaction of a model alkenyl donor/acceptor N-sulfonyltriazole with a wide selection of furans is reported. This investigation unearthed a range of structurally diverse carbocyclic and ring-opened products, in good to excellent yields. The products obtained are proposed to arise selectively via cyclopropanation or zwitterionic rearrangement pathways, which are highly dependent on both the structural and electronic features of the furan substrate.

Recent advances in transition-metal-catalyzed carbene insertion to C-H bonds

C-H functionalization has been emerging as a powerful method to establish carbon-carbon and carbon-heteroatom bonds. Many efforts have been devoted to transition-metal-catalyzed direct transformations of C-H bonds. Metal carbenes generated in situ from transition-metal compounds and diazo or its equivalents are usually applied as the transient reactive intermediates to furnish a catalytic cycle for new C-C and C-X bond formation. Using this strategy compounds from unactivated simple alkanes to complex molecules can be further functionalized or transformed to multi-functionalized compounds. In this area, transition-metal-catalyzed carbene insertion to C-H bonds has been paid continuous attention. Diverse catalyst design strategies, synthetic methods, and potential applications have been developed. This critical review will summarize the advance in transition-metal-catalyzed carbene insertion to C-H bonds dated up to July 2021, by the categories of C-H bonds from aliphatic C(sp³)-H, aryl (aromatic) C(sp²)-H, heteroaryl (heteroaromatic) C(sp²)-H bonds, alkenyl C(sp²)-H, and alkynyl C(sp)-H, as well as asymmetric carbene insertion to C-H bonds, and more coverage will be given to the recent work. Due to the rapid development of the C-H functionalization area, future directions in this topic are also discussed. This review will give the authors an overview of carbene insertion chemistry in C-H functionalization with focus on the catalytic systems and synthetic applications in C-C bond formation.

Catalytic Insertion Reactions of α-Imino Carbenoids

Over the past decade, α-imino carbenoids generated via transition metal (such as rhodium, nickel, copper, palladium, silver) catalyzed denitrogenative ring-opening of N-sulfonyl-1,2,3-triazoles have found an extensive account of applications in synthetic organic chemistry. Particularly, they have been widely utilized as a donor/acceptor carbene complex in a range of transformations leading to diverse nitrogen containing compounds and heterocycles. Along the same direction, 3-diazoindolin-2-imines were successfully applied as an alternative source of α-imino carbenoid precursors for the development of a number of methodologies to access diverse indole derivatives. This review summarizes the insertion reactions of α-imino metal carbenes derived from N-sulfonyl-1,2,3-triazoles and 3-diazoindolin-2-imines.

Catalytic Functionalization of Metallocarbenes Derived from α-Diazocarbonyl Compounds and Their Precursors

Short and efficient synthesis of heterocyclic compounds are highly desirable in synthetic organic chemistry. It is a dream approach to accomplish these syntheses from readily available starting materials in a single step. In this personal account, we discuss our contribution in the synthesis of heterocyclic compounds and beyond from N-sulfonyl-1,2,3-triazoles and α-diazocarbonyl compounds, which are the precursors for α-imino (carbonyl) metal carbenes in the presence of transition metal catalysts. Functionalization of α-imino(carbonyl) metal carbenes has been achieved through in-situ generated metal-stabilized ylides followed by either intramolecular trapping by non-polar bonds, rearrangement, cycloaddition, or 1,3-insertion fashion, which led to the efficient synthesis of various synthetically important intermediates and heterocyclic compounds.

Rh(ii)-Catalyzed denitrogenative 1-sulfonyl-1,2,3-triazole-1-alkyl-1,2,3-triazole cross-coupling as a route to 3-sulfonamido-1H-pyrroles and 1,2,3-triazol-3-ium ylides

The reaction of 1-alkyl-1H-1,2,3-triazoles with rhodium(ii) azavinyl carbenes, generated from 1-sulfonyl-1H-1,2,3-triazoles, was utilized to prepare 3-sulfonamido-1H-pyrroles and 1,2,3-triazol-3-ium ylides in good yields.

General and efficient synthesis of 1,2-dihydropyrrolo[3,4-b]indol-3-ones via a formal [3 + 2] cycloaddition initiated by C–H activation

A [Cp*RhCl₂]₂-catalyzed formal [3 + 2] cycloaddition involving a sequential coupling reaction initiated by C–H activation and aza-Michael addition has been developed for the general and efficient synthesis of 1,2-dihydropyrrolo[3,4-b]indol-3-ones.