Light-Induced Reactivity of Nucleophilic Siloxycarbene with Heterocumulenes: Synthesis of α-Ketoamides, Hydantoins, Oxoacetamidines, and Amides.

We report the reactivity of in situ-generated nucleophilic siloxycarbenes from acylsilanes via the 1,2-Brook rearrangement in the presence of visible light with heterocumulenes. This method significantly advances from the conventional use of electrophilic carbenes stabilized by metal catalysts and harsh reaction conditions. The reactivity was explored with isocyanates, carbodiimides, and -sulfinylamines to synthesize α-ketoamides, hydantoins, oxoacetamidines, and amides.

Light-Induced Transformations of Donor-Donor Diazo Compounds Derived from N-Sulfonylhydrazones.

The donor-donor carbene chemistry field is underdeveloped and often relies on harsh reaction conditions, utilizing either thermal or oxidative process with or without transition-metal catalysts. In this review, we discussed the synthesis and transformation of donor-donor diazo compounds from N-sulfonylhydrazones in the presence of light and base. The N-sulfonylhydrazones are easily accessible from the corresponding carbonyl compounds and sulfonyl hydrazides through condensation.

Light-Driven Intramolecular Cyclopropanation of Alkene-Tethered -Tosylhydrazones: Synthesis of Fused-Cyclopropane γ-Lactones.

Fused-cyclopropane ring-containing γ-lactone compounds are versatile building blocks in many fields, including the synthesis of biologically active compounds. Here, we report the light-driven intramolecular cyclopropanation of alkene-tethered -tosylhydrazones in the presence of CsCO and visible light. We have synthesized various electronically and sterically substituted and heterocyclic-containing fused-(spiro)cyclopropane γ-lactone compounds in good yields under transition metal-free conditions using a radical-free approach.

Visible-Light-Induced Siloxycarbene Addition to N═N of Azodicarboxylates: Synthesis of Acyl Hydrazides from Acylsilanes.

We report the synthesis of acyl hydrazides from acylsilanes in the presence of visible light without the aid of additives or transition metals. Acylsilanes underwent [1,2]-Brook rearrangement to generate the nucleophilic siloxycarbenes which on further addition to N═N of azodicarboxylates produced the acyl hydrazides. Control experiments indicate that the reaction proceeds through the singlet carbene intermediate.

Light-induced arylation (alkylation) of -sulfonylhydrazones with boronic acids.

Di- and triarylmethanes are an important class of compounds in many fields. Here, we report an efficient light-induced arylation (alkylation) for the synthesis of diarylmethanes, bis(diarylmethyl)benzenes, arylalkylmethanes, and triarylmethanes from readily accessible -sulfonylhydrazones and aryl/alkylboronic acids with the aid of CsCO. In the presence of light, the synthesis of diarylmethanes was also achieved from aldehydes in a one-pot manner a three-component approach in good yields.

Transition metal-catalyzed reactivity of carbenes with boronic acid derivatives for arylation (alkylation) and beyond.

This comprehensive review article discussed the reactivity of carbenes with boronic acid derivatives for the one-pot synthesis of diarylmethanes, difluoromethylated arenes, aryl and alkyl boron compounds, arylacetic acid derivatives, furan derivatives, and many other compounds. We have summarized the arylation, vinylation, and alkylation of carbenes utilizing various transition metals, . palladium, rhodium, copper, and platinum, for the construction of carbon-carbon bonds, carbon-boron bonds, and beyond through the cross-coupling strategy.

Rhodium-Catalyzed [4 + 2]-Annulation of -Acylanilines with -Sulfonyl-1,2,3-triazoles: Synthesis of 3-Aminoquinolines.

Efficient synthesis of 3-aminoquinolines has been demonstrated from readily accessible -sulfonyl-1,2,3-triazoles and -acylaniline derivatives. This transformation involves the generation of C-C and C-N bonds through insertion of rhodium azavinyl carbenoid into a N-H bond followed by cyclization and aromatization. The important features include good functional group tolerance, synthesis of indoloquinoline, and isolation of N-H-inserted product, a potential intermediate.

Synthesis of Dihydro-3,1-benzoxazine Derivatives from 1,3-Amino Alcohols and -Sulfonyl-1,2,3-triazole.

An efficient rhodium-catalyzed synthesis of dihydro-3,1-benzoxazine derivatives has been accomplished from aniline-derived 1,3-amino alcohols and -sulfonyl-1,2,3-triazole. The developed reaction demonstrates the new reactivity of azavinyl carbenes and allows access to diverse substituted dihydro-3,1-benzoxazines in good yields. Importantly, the reaction was readily extended to diols and could be used for selective protection of amino alcohols with -sulfonyl-1,2,3-triazole as the protecting reagent.

Reactivity of quinone methides with carbenes generated from α-diazocarbonyl compounds and related compounds.

Over the years, quinone methides have broadly been applied in synthesis and biological systems for synthesizing heterocyclic compounds and biologically active molecules. In this feature article, we have discussed the novel and uncovered reactivity of -quinone methides, -quinone methides, aza--quinone methides, and indolyl-2-methides with carbenes generated from α-diazocarbonyl compounds and related compounds. Two -generated transient intermediates undergo cycloannulation reactions, metathesis-type reactions, 1,6-conjugate addition reactions, cyclopropanation reactions, and many other transformations to access nitrogen- and oxygen-containing heterocyclic compounds and beyond.

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.

Denitrogenative Transformations of Pyridotriazoles and Related Compounds: Synthesis of -Containing Heterocyclic Compounds and Beyond.

The high demand for new and efficient routes toward synthesis of nitrogen-containing heterocyclic scaffolds has inspired organic chemists to discover several methodologies over recent years. This Perspective highlights one standout approach, which involves the use of pyridotriazoles and related compounds in denitrogenative transformations. Readily available pyridotriazoles undergo ring-chain isomerization to produce uniquely reactive α-diazoimines.

Light-induced metal-free transformations of unactivated pyridotriazoles.

A highly efficient and practical method for incorporation of the arylmethylpyridyl moiety into diverse molecules has been developed. This method features the transition metal-free light-induced room temperature transformation of pyridotriazoles into pyridyl carbenes, which are capable of smooth arylation, X-H insertion, and cyclopropanation reactions. The synthetic usefulness of the developed method was illustrated in a facile synthesis of biologically active molecules.

Transition-Metal- and Light-Free Directed Amination of Remote Unactivated C(sp)-H Bonds of Alcohols.

Due to the great value of amino alcohols, new methods for their synthesis are in high demand. Abundant aliphatic alcohols represent the ideal feedstock for the method development toward this important motif. To date, transition-metal-catalyzed approaches for the directed remote amination of alcohols have been well established.

Aliphatic Radical Relay Heck Reaction at Unactivated C(sp )-H Sites of Alcohols.

The Mizoroki-Heck reaction is one of the most efficient methods for alkenylation of aryl, vinyl, and alkyl halides. Given its innate nature, this protocol requires the employment of compounds possessing a halogen atom at the site of functionalization. However, the accessibility of organic molecules possessing a halogen atom at a particular site in aliphatic systems is extremely limited.

Rhodium Catalyzed Synthesis of Benzopyrans via Transannulation of N-Sulfonyl-1,2,3-triazoles with 2-Hydroxybenzyl Alcohols.

An efficient and novel rhodium-catalyzed transannulation of N-sulfonyl-1,2,3-triazoles with in situ generated o-quinone methides ( o-QMs) from 2-hydroxybenzyl alcohols has been achieved for the synthesis of substituted benzopyrans in good yields. The developed reaction involves nucleophilic attack of o-QM to α-imino rhodium carbenoid to generate a carbonyl ylide followed by 6π-electrocyclization and isomerization. Furthermore, the utility of the methodology was demonstrated in the one-pot synthesis and construction of polyheteroaromatics.

Rhodium catalyzed diastereoselective synthesis of 2,2,3,3-tetrasubstituted indolines from -sulfonyl-1,2,3-triazoles and -vinylanilines.

An efficient diastereoselective rhodium catalyzed synthesis of indolines possessing two contiguous tetrasubstituted carbon centers has been achieved with good to excellent yields using -vinylanilines and iminocarbenes derived from -sulfonyl-1,2,3-triazoles. The reaction affords excellent -diastereoselectivity through the initial formation of a -ylide followed by intramolecular trapping with unactivated alkenes an ene-type reaction with a well-organized transition state, namely intramolecular carbenylative amination of alkenes. The developed transformation was further extended to the successful synthesis of tricyclic compounds, imidazoindolines, through reduction and hypervalent iodine mediated oxidative cyclization.

One-Pot Aminoethylation of Indoles/Pyrroles with Alkynes and Sulfonyl Azides.

A general and efficient one-pot aminoethylation of substituted indoles/pyrroles was accomplished for the synthesis of various tryptamine derivatives employing a combination of alkynes and sulfonyl azides as readily accessible aminoethylating agents. The reaction features a successful integration of copper-catalyzed alkyne and azide cycloaddition to N-sulfonyl-1,2,3-triazole, rhodium-catalyzed selective insertion of α-iminocarbenes onto the C3-H bond of indoles, and reduction of the resultant enamides to tryptamine derivatives employing either NaCNBH3 or palladium catalyst, in one-pot. The reaction also showed excellent functional-group tolerance and allowed the synthesis of various substituted tryptamines in good to excellent yield.

Tandem 1,2-sulfur migration and (aza)-Diels-Alder reaction of β-thio-α-diazoimines: rhodium catalyzed synthesis of (fused)-polyhydropyridines, and cyclohexenes.

Rhodium catalyzed synthesis of substituted tetrahydropyridines was accomplished from readily accessible thio-tethered -sulfonyl-1,2,3-triazoles. The reaction involves tandem rhodium catalyzed 1,2-sulfur migration in β-thio-α-diazoimines, generated from thio-tethered -sulfonyl-1,2,3-triazoles, to thio-substituted 1-azadiene and subsequent self aza-Diels-Alder reaction. Interestingly, the methodology was effectively extended to the synthesis of fused tetrahydropyridines, dihydropyridines and cyclohexenes through the trapping of the intermediate, 1-azadiene, with various dienophiles such as enol ether, enamine, ketene ,-acetal, alkyne, alkene and diene.

An iodine(III) mediated oxidative rearrangement of enamines: efficient synthesis of α-amino ketones.

An iodine(III)-mediated, group-selective oxidative rearrangement of β,β-diarylenamines to α-amino ketones has been accomplished with excellent yield. The developed reaction involves the initial oxidation of enamine to an α-acyloxyimine intermediate and concomitant semipinacol rearrangement.

Rhodium catalyzed direct arylation of α-diazoimines.

An efficient rhodium catalyzed direct arylation of α-diazoimines, generated from readily accessible 1,2,3-triazole, has been accomplished for the synthesis of 2,2-diaryl enamides. The reaction involves the chemo- and regioselective insertion of rhodium azavinyl carbene into aromatic C(sp(2))-H bonds. Utility of the developed methodology was demonstrated in the synthesis of indole and tetrahydroisoquinoline frameworks.

Rhodium catalyzed cyanation of chelation assisted C-H bonds.

A rhodium-catalyzed cyanation of chelation assisted C-H bonds is described employing N-cyano-N-phenyl-p-methylbenzenesulfonamide as an efficient cyanating reagent. The present method allowed the synthesis of various benzonitirle derivatives in good to excellent yield. A number of chelating groups are also effective in the present cyanation of C-H bonds.