TMSOTf-Catalyzed Reactions of N-Arylynamides with Sulfilimines To Construct 2-Aminoindoles and α-Arylated Amidines

Here, we disclose an efficient TMSOTf-catalyzed C-H annulation of aryl-terminated N-arylynamides with sulfilimines, leading to the practical assembly of various valuable 2-aminoindoles in generally moderate to excellent yields with a broad range of functional groups, while nonaryl terminated N-arylynamides undergo TMSOTf-catalyzed aminative arylation with sulfilimines providing α-arylated amidines.

Recyclable gold(I)-catalyzed heterocyclization of ynamides with benzyl or indolyl azides towards 2-aminoindoles or 3-amino-β-carbolines

A highly efficient heterogeneous gold(I)-catalyzed heterocyclization of ynamides with benzyl or indolyl azides has been achieved in 1,2-dichloroethane under mild conditions via a heterogenized α-imino gold carbene intermediate using 5 mol% of SBA-15-anchored strongly hindered NHC-gold(I) complex [IPr-SBA-15-AuNTf2] as the catalyst, delivering a wide range of valuable 2-aminoindoles or 3-amino-β-carbolines in mostly good to excellent yields with high regioselectivity. Furthermore, the new heterogenized NHC-gold(I) complex displays the same catalytic activity as IPrAuNTf2 and is facile to recover by centrifugation of the reaction mixture and can be reused at least seven times without any appreciable drop in its catalytic activity.

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.

Metal-Free [3+2] Annulation of Ynamides with Anthranils to Construct 2-Aminoindoles

A novel metal-free [3+2] annulation of ynamides with anthranils provides a facile, flexible, environmentally friendly, and atom-economical route to 2-aminoindoles. This synthetic process proceeds with efficiency, excellent regioselectivity, and wide functional group tolerance under mild conditions. Moreover, the obtained 2-aminoindole products represent a multifunctional platform for the construction of various 2-aminoindolyl frameworks.

Recent advances in the synthesis of indole embedded heterocycles with 3-diazoindolin-2-imines

The preparations, reactivity and synthetic applications of 3-diazoindolin-2-imines, a valuable class of α-diazo amidines, are reviewed.

Synthesis of 8-Alkoxy-5H-isochromeno[3,4-c]isoquinolines and 1-Alkoxy-4-arylisoquinolin-3-ols through Rh(III)-Catalyzed C-H Functionalization of Benzimidates with 4-Diazoisochroman-3-imines and 4-Diazoisoquinolin-3-ones

Rh(III)-catalyzed C-H activation/annulation of benzimidates with 4-diazoisochroman-3-imines furnished 8-alkoxy-5H-isochromeno[3,4-c]isoquinolines in moderate to excellent yields with a broad range of substrate scope. The reaction was carried out under mild reaction conditions and could be scaled up with practical usage. Similar reaction between benzimidates and 4-diazoisoquinolin-3-ones provided 1-alkoxy-4-arylisoquinolin-3-ols in excellent yields. Moreover, the synthesized products could be conveniently transformed to the corresponding heterocycles with a 1,8-naphthyridinone or isochromenopyridinone core, which are privileged structures in medicinal chemistry.

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.

General Approach To Construct Azepino[2,3-b:4,5-b']diindoles, Azocino[2,3-b:4,5-b']diindoles, and Azonino[2,3-b:4,5-b']diindoles via Rh(II)-Catalyzed Reactions of 3-Diazoindolin-2-imines with 3-(Bromoalkyl)indoles

Rh(II)-catalyzed reactions of 3-diazoindolin-2-imines with 3-(2-bromoethyl)indoles, 3-(3-bromopropyl)indoles, and 3-(4-bromobutyl)indoles, followed by treatment with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in a one-pot operation furnished azepino[2,3-b:4,5-b']diindoles, azocino[2,3-b:4,5-b']diindoles, and azonino[2,3-b:4,5-b']diindoles, respectively. Structural uniqueness of the products, broad substrate scope, mild reaction conditions, and readily available starting materials are the merits of this approach.

Preparation of spiro[imidazolidine-4,3′-indolin]-2′-imines via copper(i)-catalyzed formal [2 + 2 + 1] cycloaddition of 3-diazoindolin-2-imines and triazines

We report a facile and efficient synthesis of spiro[imidazolidine-4,3′-indolin]-2′-imines via a copper(i)-catalyzed cascade reaction of 3-diazoindolin-2-imines with 1,3,5-triazines.

Convenient synthesis of 2-amino-3-(arylthio)indoles via the Rh-catalyzed reaction of 3-diazoindol-2-imines with thioesters

2-Amino-3-(arylthio)indoles were conveniently synthesized via the Rh(ii)-catalyzed C–S/N–C coupling reaction between 3-diazoindol-2-imines and thioesters.

A copper-catalyzed reaction of 3-diazoindolin-2-imines with 2-(phenylamino)ethanols: convenient access to spiro[indoline-3,2′-oxazolidin]-2-imines

3-Diazoindolin-2-imines reacted with chiral 2-(phenylamino)ethanols under copper catalysis to furnish chiral spiro[indoline-3,2′-oxazolidin]-2-imines in good yields with excellent diastereoselectivity.

A novel approach to 5H-pyrazino[2,3-b]indolesviaannulation of 3-diazoindolin-2-imines with 2H-azirines or 5-alkoxyisoxazoles under Rh(ii) catalysis

The first example of rhodium carbenoid-mediated intermolecular annulation of cyclic diazo compounds with azirines and alkoxyisoxazoles is presented.

Facile synthesis of pyrroloindoles via a rhodium(ii)-catalyzed annulation of 3-benzylidene-indolin-2-ones and α-imino carbenes

A novel carbenoid strategy to construct pyrrole-fused indole alkaloids.

TfOH-Catalyzed Reaction between 3-Diazoindolin-2-imines and Electron-Rich Arenes: Access to 3-Aryl-2-aminoindoles

TfOH-catalyzed reactions between 3-diazoindolin-2-imines and electron-rich arenes were disclosed. These metal-free reactions furnished 3-aryl-2-aminoindoles in moderate to excellent yields with the tolerance of a broad range of functional groups.

Rhodium-Catalyzed Cycloadditions between 3-Diazoindolin-2-imines and 1,3-Dienes

Azepino[2,3-b]indoles were regioselectively prepared through rhodium-catalyzed formal aza-[4 + 3] cycloaddition between 3-diazoindolin-2-imines and 1,3-dienes in moderate to good yields. Using 2-[(trimethylsilyl)oxy]-1,3-butadiene as the diene component, azepino[2,3-b]indol-4(1H)-ones were constructed. Furthermore, the reactions of cyclic dienes, such as 1,3-cyclohexadiene and 1,3-cyclopentadiene, furnished the corresponding [3 + 2] cycloaddition products.

Convenient preparation of 4-diazoisochroman-3-imines and 3-subsituted 3,5-dihydroisochromeno[3,4-d][1,2,3]triazoles

4-Diazoisochroman-3-imines were prepared via the Cu(i)-catalyzed reaction of (2-ethynylphenyl)methanols with sulfonyl azides, and converted to 3,5-dihydroisochromeno[3,4-d][1,2,3]triazoles by reaction with primary amines under catalyst-free conditions.

Preparation of 3-azoindoles and 3-hydrazonoindolin-2-imines as well as their applications as NNO pincer ligands for boron

Potassium carbonate-promoted coupling reactions between 3-diazoindolin-2-imines and nucleophiles were tested.