Transition-metal-catalyzed denitrogenative transannulation: converting triazoles into other heterocyclic systems

One-step synthesis of nitrogen-containing medium-sized rings via α-imino diazo intermediates

Eight- and 9-membered dioxazocines and dioxazonines are readily synthesized starting from N-sulfonyl-1,2,3-triazoles in a single-step procedure. A perfect regioselectivity and generally good yields (up to 92%) are obtained under dirhodium catalysis using 1,3-dioxolane and 1,3-dioxane as solvents and reagents.

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.

Synthesis of pyrroles from terminal alkynes, N-sulfonyl azides, and alkenyl alkyl ethers through 1-sulfonyl-1,2,3-triazoles

A method for synthesis of substituted pyrroles has been developed. 1-Sulfonyl-1,2,3-triazoles generated from terminal alkynes gave α-imino rhodium carbene complexes, which when reacted with alkenyl alkyl ethers afforded substituted pyrroles. The method can be efficiently applied to a one-pot sequential reaction starting from terminal alkynes.

Intramolecular dearomatizing [3 + 2] annulation of α-imino carbenoids with aryl rings furnishing 3,4-fused indole skeletons

The rhodium-catalyzed dearomatizing [3 + 2] annulation reaction of 4-(3-arylpropyl)-1,2,3-triazoles is described. It provides a straightforward synthetic pathway from simple 5-aryl-1-alkynes leading to tricyclic 3,4-fused dihydroindoles via the corresponding 1,2,3-triazoles.

Iridium-catalyzed intermolecular azide-alkyne cycloaddition of internal thioalkynes under mild conditions

An iridium-catalyzed azide-alkyne cycloaddition reaction (IrAAC) of electron-rich internal alkynes is described. It is the first efficient intermolecular AAC of internal thioalkynes. The reaction exhibits remarkable features, such as high efficiency and regioselectivity, mild reaction conditions, easy operation, and excellent compatibility with air and a broad spectrum of organic and aqueous solvents. It complements the well-known CuAAC and RuAAC click reactions.

Palladium-catalyzed regioselective azidation of allylic C–H bonds under atmospheric pressure of dioxygen

A palladium-catalyzed allylic azidation of alkenes with sodium azide under atmospheric pressure of dioxygen was developed.

Unprecedented synthesis of aza-bridged benzodioxepine derivatives through a tandem Rh(ii)-catalyzed 1,3-rearrangement/[3+2] cycloaddition of carbonyltriazoles

Rh(ii)-catalyzed novel tandem intramolecular cycloisomerizations of aldehydes or ketones with 1-sulfonyl 1,2,3-triazoles have been disclosed, providing a facile protocol to access a series of functionalized aza-bridged benzodioxepine heterocycles.

The stereoselective synthesis of α-amino aldols starting from terminal alkynes

A new sequential procedure for the stereoselective synthesis of syn α-amino β-oxy ketones starting from terminal alkynes has been developed.

Stereoselective 1,3-insertions of rhodium(II) azavinyl carbenes

Rhodium(II) azavinyl carbenes, conveniently generated from 1-sulfonyl-1,2,3-triazoles, undergo a facile, mild, and convergent formal 1,3-insertion into N-H and O-H bonds of primary and secondary amides, various alcohols, and carboxylic acids to afford a wide range of vicinally bisfunctionalized (Z)-olefins with perfect regio- and stereoselectivity. Utilizing the distinctive functionality installed through these reactions, a number of subsequent rearrangements and cyclizations expand the repertoire of valuable organic building blocks constructed by reactions of transition-metal carbene complexes, including α-allenyl ketones and amino-substituted heterocycles.

Highly enantioselective dearomatizing formal [3+3] cycloaddition reactions of N-acyliminopyridinium ylides with electrophilic enol carbene intermediates

A effective dearomatizing formal [3+3]-cycloaddition reaction triggered by Rh(II)-catalyzed dinitrogen extrusion of enoldiazoacetates followed by vinylogous addition of metal enolcarbenes to N -acyliminopyridinium ylides that produces highly substituted 1,2,3,6-tetrahydropyridazines in up to 98% ee and in high yield has been developed.

Intramolecular transannulation of alkynyl triazoles via alkyne-carbene metathesis step: access to fused pyrroles

An intramolecular Rh-catalyzed transannulation reaction of alkynyl triazoles has been developed. This method allows efficient construction of various 5,5-fused pyrroles, including tetrahydropyrrolo and spiro systems. The method demonstrates excellent functional group compatibility. A rhodium carbene-alkyne metathesis mechanism is proposed for this transformation.

Regiocontrolled synthesis of polysubstituted pyrroles starting from terminal alkynes, sulfonyl azides, and allenes

1-Sulfonyl-1,2,3-triazoles, readily prepared from terminal alkynes and sulfonyl azides, react with allenes in the presence of a nickel(0) catalyst to produce the corresponding isopyrroles. The initially produced isopyrroles are further converted to a wide range of polysubstituted pyrroles through double bond transposition and Alder-ene reactions.

Transannulation of 1-sulfonyl-1,2,3-triazoles with heterocumulenes

Readily available 1-mesyl-1,2,3-triazoles are efficiently converted into a variety of imidazolones and thiazoles by Rh(II)-catalyzed denitrogenative reactions with isocyanates and isothiocyanates, respectively. The proposed triazole-diazoimine equilibrium results in the formation of highly reactive azavinyl metal-carbenes, which react with heterocumulenes causing an apparent swap of 1,2,3-triazole core for another heterocycle.