Relayed Heteroatom Group Transfer: A Structural Reorganization between Bisthioester and Triaminophosphine to α,α-Disulfenylamide

Simultaneous multiple displacements of organic molecules can lead to a large structural reconstruction with increased complexity that would be difficult to access otherwise. Whereas double displacement such as olefin metathesis is well-established, higher-order versions remain much more challenging, because of their intrinsic thermodynamic disadvantages. Here, we describe a newly discovered relayed heteroatom group transfer process between bisthioesters and triaminophosphines as an unusual example of a formal triple displacement. Through the oxygen/nitrogen exchange between the two simple starting materials, in addition to the 1,2-sulfur migration of a putative carbene intermediate, an organized relocation of the O/S/N groups proceeded to give a variety of α,α-disulfenylamides with excellent efficiency under ambient conditions. The experimental and computational mechanistic studies revealed the sequence of the relayed group shifts via an α,α-disulfenyl phosphonium enolate intermediate as well as the dual role of triaminophosphine as both an oxygen acceptor and a nitrogen donor.

Substrate-Dependent Denitrogenative Rearrangements of Rhodium Azavinyl Carbenes Involving 1,2-Aryl Migration

Herein, we disclose substrate-dependent rearrangements of 4-substituted N-sulfonyl-1,2,3-triazoles under Rh(II)-catalysis via denitrogenation. The reaction pathways included key 1,2-aryl migration via the formation of intermediatory phenonium ion, which is elusive so far with Rh-azavinyl carbenes. Intriguingly, the transformations were completely dependent on the substituent present leading to different scaffolds like enaminones, pyrrol-3-ones, and azadienes. Hammett studies provided essential insights into the carbocationic intermediate formation. The developed methodology featured simple reaction conditions, excellent functional group compatibility, and broad substrate scope.

Access to tetrahydrocarbazoles and pyrrolo[3,4-b]carbazoles through sequential reactions of triazoles and indoles

Tetrahydrocarbazoles and pyrrolo[3,4-b]carbazoles could be synthesized conveniently through sequential reactions of ester-tethered 1-sulfonyl-1,2,3-triazoles and indoles. The reaction conditions were mild and the procedures were quite simple. Moreover, the key intermediate α,β-unsaturated imine acted as a [2C] synthon in the [4 + 2] cycloaddition reaction, and the imino group could be used as a nucleophile to construct the fourth ring.

1,2-Acyl migration with α-imino rhodium carbenoids leading to substituted 1-naphthols

A unique method for the synthesis of substituted 1-naphthols by a rhodium(II)-catalysed ring-expansion reaction of 2-triazolyl-1-indanone derivatives is reported. 1,2-Acyl migration occurs with an intermediate α-imino rhodium carbenoid generated from the triazolyl moiety.

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.

Synthesis of benzothiazonine by rhodium-catalyzed denitrogenative transannulation of 1-sulfonyl-1,2,3-triazole and thiochromone

A facile synthesis of multi-functionalized benzothiazonine was achieved by the rhodium-catalyzed denitrogenative annulation of 1-sulfonyl-1,2,3-triazole and thiochromone. In view of the excellent atom economy, broad substrate scope and easy availability of starting materials, the protocol provided an efficient strategy for the construction of medium N,S-heterocycles.

Domino Construction of Benzoxazole-Derived Sulfonamides via Metal-Free Denitrogenation of 5-Iodo-1,2,3-triazoles in the Presence of SO2 and Amines

A straightforward domino approach to assemble benzoxazole-derived sulfonamides has been developed. The method is based on annulation-induced in situ generation of diazo compounds from readily available 2-(5-iodo-1,2,3-triazolyl)phenols, followed by metal-free denitrogenative transformation upon the action of 1,4-diazabicyclo[2.2.2]octane bis(sulfur dioxide) (DABSO) and amines. The protocol is operationally simple and features a broad substrate scope, furnishing a library of target compounds in generally good yields.

Assembly of Thiosubstituted Benzoxazoles via Copper-Catalyzed Coupling of Thiols with 5-Iodotriazoles Serving as Diazo Surrogates

An efficient cascade approach to thiosubstituted benzoxazoles has been developed. The transformation starts with in situ generation of a diazo compound via annulation-triggered electrocyclic opening of the 1,2,3-triazole ring. The subsequent Cu-catalyzed trapping of diazo intermediates by various thiols affords the desired heterocycles in generally good yields of up to 91%. The protocol features very good functional group tolerance and is applicable to substrates with different electronic properties.

Rhodium-catalyzed Sommelet–Hauser type rearrangement of α-diazoimines: synthesis of functionalized enamides

An efficient rhodium catalyzed Sommelet–Hauser type rearrangement of sulfur ylides derived from α-thioesters and N-sulfonyl-1,2,3-triazoles has been successfully accomplished for the synthesis of various functionalized enamides.

Intramolecular azavinyl carbene-triggered rearrangement of furans

An intramolecular rhodium-catalyzed reaction of 1-tosyl-1,2,3-triazoles with furans has been explored. The tosylimino functionality was found to play a significant chemical role participating in the subsequent domino-transformations of a key reaction intermediate. One of the reaction pathways leads to valuable 2-formyl- and 2-acetylpyridine building blocks, which could be obtained in one-pot starting from easily accessible (furan-2-ylmethyl)propargyl amines. An original method for the synthesis of highly functionalized indolizines from the obtained pyridines has been proposed.

Mechanisms of phosphine-catalyzed [3+3] cycloaddition of ynones and azomethine imines: a DFT study

Mechanisms of PPh₃-catalyzed [3+3] cycloaddition between a ynone and an azomethine imine.

Thio-Michael addition of thioamides and allenes for the selective construction of polysubstituted 2-arylthiophenes via TBAI/H2O2 promoted tandem oxidative annulation and 1,2-sulfur migration

A novel TBAI-catalyzed tandem thio-Michael addition/oxidative annulation of allenes and thioamides for the construction of polysubstituted 2-arylthiophenes under a sulfur migration transformation protocol has been developed. The transition-metal-free protocol achieves the oxidative cyclization reaction of thioamides containing electron-rich substituents with allenes to construct polysubstituted thiophenes selectively by controlling oxidation conditions.

Zinc-catalyzed reaction of isoxazoles with thioynol ethers involving an unprecedented 1,2-sulfur migration

A novel zinc-catalyzed reaction of isoxazoles with thioynol ethers involving an unprecedented 1,2-sulfur migration has been developed, which represents the first example of a non-noble metal-catalyzed reaction between isoxazoles and alkynes. This method allows the facile and atom-economical synthesis of a range of valuable β-keto enamides. Moreover, the computational study provides further evidence for the feasibility of the proposed reaction mechanism.

Metal-free synthesis of 2-aminonaphthalenes by intramolecular transannulation of 1-sulfonyl-4-(2-alkenylphenyl)-1,2,3-triazoles

A facile metal-free synthesis of naphthalenes by intramolecular transannulation of 1-sulfonyl-4-(2-alkenylphenyl)-1,2,3-triazoles was realized. The in situ formed ketenimine was proposed as the key intermediate, and the desired 2-aminonaphthalenes were generated in up to 87% yield in refluxing 1,2-dichloroethane without any catalyst or additive.

Diversity-oriented synthesis of heterocycles and macrocycles by controlled reactions of oxetanes with α-iminocarbenes

Using N-sulfonyl triazoles as substrates, compounds as diverse as 2-imino tetrahydrofurans, 13- and 15-membered ring aza-macrocycles can be prepared selectively via formal [1 + 4], [5 + 4 + 4] and [3 + 4 + 4 + 4] condensations of α-imino carbenes and oxetanes under Rh(ii)-catalysis or thermal activation. Spirocyclic N-heterocycles are also accessible by means of Buchwald-Hartwig and Pictet-Spengler cyclizations. By reaction control, substrate selection or further derivatization, a large variety of chemical structures is thus achievable. Finally, using triazoles reacting under thermal activation, interesting mechanistic insight was obtained.

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.

Rhodium(ii)-catalyzed intermolecular [3 + 2] annulation of N-vinyl indoles with N-tosyl-1,2,3-triazoles via an aza-vinyl Rh carbene

This study opens up a new synthetic approach for the construction of various functionalized indoles having a dihydropyrrole moiety from the Rh(ii)-catalyzed annulation of N-vinyl indoles with 4-aryl-N-tosyl-1,2,3-triazoles under mild conditions.

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

An efficient diastereoselective rhodium catalyzed synthesis of indolines possessing two contiguous tetrasubstituted carbon centers has been achieved with good to excellent yields using ortho-vinylanilines and iminocarbenes derived from N-sulfonyl-1,2,3-triazoles.

An efficient diastereoselective rhodium catalyzed synthesis of indolines possessing two contiguous tetrasubstituted carbon centers has been achieved with good to excellent yields using ortho-vinylanilines and iminocarbenes derived from N-sulfonyl-1,2,3-triazoles. The reaction affords excellent cis-diastereoselectivity through the initial formation of a N-ylide followed by intramolecular trapping with unactivated alkenes via 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.

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.

Straightforward regioselective construction of 3,4-dihydro-2H-1,4-thiazine by rhodium catalysed [3 + 3] cycloaddition of thiirane with 1-sulfonyl-1,2,3-triazole: a pronounced acid additive effect

A rhodium catalyzed regioselective coupling of thiirane with 1-sulfonyl-1,2,3-triazole has been realized to give a formal [3 + 3] cycloaddition product 3,4-dihydro-2H-1,4-thiazine via the 1,3-insertion model of azavinyl carbene.

Base-induced synthesis of N-dialkylaminomethyl-2H-1,2,3-triazoles from N-sulfonyl-1,2,3-triazoles

A facile synthetic method to access N-dialkylaminomethyl-2H-1,2,3-triazoles has been developed from N-sulfonyl-1,2,3-triazoles by a base induced reaction. Moreover, 4-phenyl-1H-1,2,3-triazoles can also give the same product even in the absence of a base at high temperature.

A new method to access triazole-fused spiro-guanidines from the reaction of isothiocyanates tethered N-sulfonyl-1,2,3-triazoles and amines

The reaction of isothiocyanate tethered N-sulfonyl-1,2,3-triazoles and amines afforded asymmetrical guanidines in fair to excellent yields through a two-component tandem reaction process.

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 N-sulfonyl-1,2,3-triazoles. The reaction involves tandem rhodium catalyzed 1,2-sulfur migration in β-thio-α-diazoimines, generated from thio-tethered N-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 in situ trapping of the intermediate, 1-azadiene, with various dienophiles such as enol ether, enamine, ketene S,S-acetal, alkyne, alkene and diene. Furthermore, the direct conversion of propargyl sulfides to (fused)-tetrahydropyridines was also achieved through the successful integration of copper and rhodium catalysts in one-pot.

Rhodium(II)-Catalyzed Annulation of Azavinyl Carbenes Through Ring-Expansion of 1,3,5-Trioxane: Rapid Access to Nine-Membered 1,3,5,7-Trioxazonines

The rhodium(II)-catalyzed denitrogenative coupling of N-alkylsulfonyl 1,2,3-triazoles with 1,3,5-trioxane led to nine-membered-ringed trioxazonines in moderate-to-good yields. 1,3,5-Trioxane, acting as an oxygen nucleophile, reacted with the α-aza-vinylcarbene intermediate, giving rise to ylide formation, which was probably the key step in the reaction. Triazoles that contained aryl substituents with various electronic and steric features on the C4 carbon atom were well-tolerated. The synthesis of trioxazonine derivatives was achieved through a one-pot, two-step procedure from 1-mesylazide and a terminal alkyne by combining Cu(I)-catalyzed 1,3-dipolar cycloaddition and rhodium-catalyzed transformations.