Synthesis of Fluorenes via Tandem Copper-Catalyzed [3 + 2] Cycloaddition and Rhodium-Catalyzed Denitrogenative Cyclization in a 5-Exo Mode from 2-Ethynylbiaryls and N-Sulfonyl Azides in One Pot

Rh2(II)-Catalyzed Enantioselective Intramolecular Büchner Reaction and Aromatic Substitution of Donor-Donor Carbenes

The chiral dirhodium(ii) tetracarboxylate-catalyzed enantioselective intramolecular Büchner reaction of donor/donor-carbenes was reported and a series of valuable chiral polycyclic products were synthesized. Both aryloxy enynones and diazo compounds were efficient carbene precursors for this reaction. Excellent yields (up to 99%) and outstanding enantioselectivities (up to >99% ee) were achieved under standard conditions. For furyl substituted chiral cyclohepta[b]benzofurans bearing a substituent at the C4 position on cycloheptatrienes, control reactions showed that the chiral Büchner products could slowly racemize either under dark or natural light conditions. A diradical-involved mechanism rather than a zwitterionic intermediate was proposed to explain the racemization. Furthermore, furyl substituted chiral fluorene derivatives were obtained via asymmetric aromatic substitution when biaryl enynones were employed as carbene precursors.

The chiral dirhodium(ii) tetracarboxylate-catalyzed enantioselective intramolecular Büchner reaction and aromatic substitution of donor/donor-carbenes were reported and a series of valuable chiral polycyclic products were synthesized.

Regitz Diazo Transfer Reaction for the Synthesis of 1,4,5-Trisubstituted 1,2,3-Triazoles and Subsequent Regiospecific Construction of 1,4-Disubstituted 1,2,3-Triazoles via C-C Bond Cleavage

A straightforward and efficient methodology has been developed for the synthesis of 1,4,5-trisubstituted dicarbonyl 1,2,3-triazoles and 1,4-disubstituted sole-carbonyl 1,2,3-triazoles via a C-C bond cleavage process. The Regitz diazo transfer and C-C bond cleavage were the key steps of this transformation, which provided diverse carbonyl-substituted structural 1,2,3-triazoles. This reaction featured with excellent regioselectivity, wide functional group tolerance, and mild conditions.

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.

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.

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.

Catalytic Divergent [3+3]- and [3+2]-Cycloaddition by Discrimination Between Diazo Compounds

Highly selective divergent cycloaddition reactions of enoldiazo compounds and α-diazocarboximides catalyzed by copper(I) or dirhodium(II) have been developed. With tetrakis(acetonitrile)copper(I) tetrafluoroborate as the catalyst epoxypyrrolo[1,2-a]azepine derivatives were prepared in good yields and excellent diastereoselectivities through the first reported [3+3]-cycloaddition of a carbonyl ylide. Use of Rh2 (pfb)4 or Rh2 (esp)2 directs the reactants to regioselective [3+2]-cycloaddition generating cyclopenta[2,3]pyrrolo[2,1-b]oxazoles with good yields and excellent diastereoselectivities.

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 Intramolecular Transannulation Reaction of Alkynyl Thiadiazole Enabled 5,n-Fused Thiophenes

A method for the synthesis of a wide range of fused thiophenes, including those fused with lactams, lactones, or cyclic ethers, was developed from a rhodium-catalyzed intramolecular transannulation reaction of alkynyl thiadiazoles. This transannulation reaction provides an efficient platform for the construction of a variety of 5,n-fused thiophenes from readily available starting materials together with the release of molecular nitrogen.

Rhodium-catalyzed synthesis of 1,2-dihydropyridine by a tandem reaction of 4-(1-acetoxyallyl)-1-sulfonyl-1,2,3-triazole

A tandem reaction of 4-(1-acetoxyallyl)-1-sulfonyl-1,2,3-triazole involving α-imino rhodium carbene was reported and 1,6-dihydropyridin-3-yl acetate was obtained.

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.

1,3-Dien-5-ynes: Versatile Building Blocks for the Synthesis of Carbo- and Heterocycles

1,3-Dien-5-ynes have been extensively used as starting materials for the synthesis of a wide number of different carbo- and heterocycles. The aim of this review is to give an overview of their utility in organic synthesis, highlighting the variety of compounds that can be directly accessed from single reactions over these systems. Thus, cycloaromatization processes are initially commented, followed by reactions directed toward the syntheses of five-membered rings, other carbocycles and, finally, heterocycles. The diverse methodologies that have been developed for the synthesis of each of these types of compounds from 1,3-dien-5-ynes are presented, emphasizing the influence of the reaction conditions and the use of additional reagents in the outcome of the transformations.

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.

Rhodium(ii)-catalyzed intramolecular annulation of 1-sulfonyl-1,2,3-triazoles with indoles: facile synthesis of functionalized tetrahydro-β-carbolines

A novel rhodium(ii)-catalyzed intramolecular annulation of 1-sulfonyl-1,2,3-triazoles with indoles has been developed, which enables the facile synthesis of various 4-functionalized tetrahydro-β-carbolines and relevant scaffolds from readily available starting materials.

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.