One-Pot Procedure for the Introduction of Three Different Bonds onto Terminal Alkynes throughN-Sulfonyl-1,2,3-Triazole Intermediates

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.

α-Diazo Sulfonium Triflates: Synthesis, Structure, and Application to the Synthesis of 1-(Dialkylamino)-1,2,3-triazoles

The one-pot synthesis of a series of sulfonium salts containing transferable diazomethyl groups is described, and the structure of these compounds is elucidated by X-ray crystallography. Under photochemical conditions, reaction of these salts with N,N-dialkyl hydrazones affords 1-(dialkylamino)-1,2,3-triazoles via diazomethyl radical addition to the azomethine carbon followed by intramolecular ring closure. The straightforward transformation of the structures thus obtained into mesoionic carbene-metal complexes is also reported and the donor properties of these new ligands characterized.

Renaissance of Ring-Opening Chemistry of Benzotriazoles: New Wine in an Old Bottle

1,2,3-Benzotriazoles could undergo ring cleavage to form ortho-amino arenediazonium or α-diazo-imine species via a Dimroth-type equilibrium. Historically, the synthetic potential of this unique reactivity had remained underdeveloped. Recently, some new strategies have been developed to effect the ring-opening chemistry of benzotriazoles in more practical manners. A wide range of conceptually novel and synthetically useful reactions have been developed, which enable the access to diverse valuable heterocycles and ortho-amino arene derivatives. As one of the players in this field, our group has also contributed a series of intriguing transition-metal-catalyzed denitrogenative functionalizations of benzotriazoles. In this account, we aim to provide an overview of the ring-opening chemistry of benzotriazoles, with a focus on relevant works published in the past decade. In order to show a whole picture of the research field, some pioneering works in its developing history will also be discussed briefly.

The Expanding Utility of Rhodium-Iminocarbenes: Recent Advances in the Synthesis of Natural Products and Related Scaffolds

Rhodium-iminocarbenes that are derived from N-sulfonyl-1,2,3-triazoles have become an important class of reactive species and useful intermediates in organic synthesis. Over the last several years, many practical and versatile approaches involving rhodium-iminocarbene intermediates to synthetically challenging molecules (scaffolds) have been developed. This Minireview mainly summarizes the recent advance of rhodium-iminocarbene involved reactions in the synthesis of natural products and their related scaffolds by the end of 2017. Several applications in important pharmaceuticals are documented as well.

Recent advances in the application of indoles in multicomponent reactions

Indoles are some of the most versatile and common nitrogen-based heterocyclic scaffolds and are frequently used in the synthesis of various organic compounds. Indole based compounds are very important among heterocyclic structures due to their biological and pharmaceutical activities. The last decade, in particular, has witnessed considerable activity towards the synthesis of indole derivatives due to the possibilities for the design of polycyclic structures by the incorporation of multiple fused heterocyclic scaffolds in an attempt to achieve promising new heterocycles with chemical and biomedical relevance. In this study, we provide an overview on recent applications of indole in the multicomponent reactions for the synthesis of various heterocyclic compounds during the period of 2012 to 2017.

Calcium carbide catalytically activated with tetra-n-butyl ammonium fluoride for Sonogashira cross coupling reactions

We report a novel method for the direct synthesis of mono- and bis-arylated alkynes utilizing catalytically activated CaC₂ as the alkyne component.

Rhodium-catalyzed NH insertion of pyridyl carbenes derived from pyridotriazoles: a general and efficient approach to 2-picolylamines and imidazo[1,5-a]pyridines

A general and efficient NH insertion reaction of rhodium pyridyl carbenes derived from pyridotriazoles was developed. Various NH-containing compounds, including amides, anilines, enamines, and aliphatic amines, smoothly underwent the NH insertion reaction to afford 2-picolylamine derivatives. The developed transformation was further utilized in a facile one-pot synthesis of imidazo[1,5-a]pyridines.

Rhodium(II)-catalyzed intramolecular cycloisomerizations of methylenecyclopropanes with N-sulfonyl 1,2,3-triazoles

A novel rhodium(II)-catalyzed tandem cycloisomerization of methylenecyclopropanes (MCPs) with N-sulfonyl 1,2,3-triazoles is disclosed. The reaction produces a series of highly functionalized polycyclic N heterocycles via a rhodium imino carbene intermediate. A distinct feature of this divergent synthesis is that different types of substrates control the reaction pathways. Moreover, several interesting transformations of these products to construct diazabicyclo[3.2.1]octane derivatives are also reported.

Catalytic asymmetric transannulation of NH-1,2,3-triazoles with olefins

A convenient one-pot asymmetric synthesis of 2,3-dihydropyrroles from in situ generated triflated triazoles and olefins is described that further expands the utility of azavinyl carbene chemistry and provides access to an important class of cyclic enamides. Mechanistic investigations support the involvement of triflated cyclopropylaldimine intermediates in the formation of 2,3-dihydropyrrole. To the best of our knowledge, this is the first example of a chiral Brønsted acid catalyzed rearrangement of cyclopropylimines into enantioenriched 2,3-dihydropyrroles.

Rhodium-catalyzed tandem cyclopropanation/Cope rearrangement of 4-alkenyl-1-sulfonyl-1,2,3-triazoles with dienes

Take your pick… A practical method for the synthesis of structurally diverse rhodium vinylcarbenes from stable 1-sulfonyl-1,2,3-triazole precursors has been developed. The reaction is general for a broad range of 4-alkenyl triazoles and dienes, enabling the stereoselective synthesis of a variety of polycyclic imines, which are readily converted into amines or aldehydes in a one-pot process.