Metal Cocatalyzed Tandem Alkynylative Cyclization Reaction of in Situ Formed N-Iminoisoquinolinium Ylides with Bromoalkynes via C–H Bond Activation

Synthesis of 2-(Trifluoromethyl)-[1,2,4]triazolo[5,1-a]isoquinoline via Cycloaddition of C,N-Cyclic Azomethine Imine with CF3CN

A [3 + 2] cycloaddition of C,N-cyclic azomethine imine with in situ-generated CF3CN for the construction of 2-(trifluoromethyl)-[1,2,4]triazolo[5,1-a]isoquinoline is reported. Remarkably, this process shows a broad substrate scope with excellent functional group tolerance, which is scalable and enables a practical route to a library of 2-(trifluoromethyl)-[1,2,4]triazolo[5,1-a]isoquinoline derivatives in moderate to good yields.

Base-mediated [3 + 2]-cycloannulation strategy for the synthesis of pyrazolo[1,5-a]pyridine derivatives using (E)-β-iodovinyl sulfones

Pyrazolo[1,5-a]pyridines continue to occupy a special place in medicinal chemistry, but the direct construction of 3-sulfonyl analogues remains unexplored. Under basic conditions, pyridinium-N-amine and the corresponding dipolar aminide played a vibrant role in [3 + 2]-cycloaddition using (E)-β-iodovinyl sulfones. K₂CO₃-mediated tandem cycloannulative-desulfonylation of (E)-β-iodovinyl sulfones with 1-aminopyridinium iodide is realized to access 2-substituted pyrazolo[1,5-a]pyridines in good to high yields. An essential modification of the dipolar N-tosylpyridinium imide allows the first preparative synthesis of 3-sulfonyl-pyrazolo[1,5-a]pyridines in moderate to high yields. Of note, the metal-free protocol features a broad substrate scope with good functional group tolerance and compatibility. The efficacy of the process was proved with gram-scale reactions, and a plausible mechanism is also presented based on concrete results.

Transition Metal-Catalyzed Reactions of Alkynyl Halides

BACKGROUND

Transition metal-catalyzed reactions of alkynyl halides are a versatile means of synthesizing a wide array of products. Their use is of particular interest in cycloaddition reactions and in constructing new carbon-carbon and carbon-heteroatom bonds. Transition metal-catalyzed reactions of alkynyl halides have successfully been used in [4+2], [2+2], [2+2+2] and [3+2] cycloaddition reactions. Many carbon-carbon coupling reactions take advantage of metal-catalyzed reactions of alkynyl halides, including Cadiot-Chodkiewicz, Suzuki-Miyaura, Stille, Kumada-Corriu and Inverse Sonogashira reactions. All the methods of constructing carbon-nitrogen, carbon-oxygen, carbon-phosphorus, carbon-sulfur, carbon-silicon, carbon-selenium and carbon-tellurium bonds employed alkynyl halides.

OBJECTIVE

The purpose of this review is to highlight and summarize research conducted in transition metalcatalyzed reactions of alkynyl halides in recent years. The focus will be placed on cycloaddition and coupling reactions, and their scope and applicability to the synthesis of biologically important and industrially relevant compounds will be discussed.

CONCLUSION

It can be seen from the review that the work done on this topic has employed the use of many different transition metal catalysts to perform various cycloadditions, cyclizations, and couplings using alkynyl halides. The reactions involving alkynyl halides were efficient in generating both carbon-carbon and carbonheteroatom bonds. Proposed mechanisms were included to support the understanding of such reactions. Many of these reactions face retention of the halide moiety, allowing additional functionalization of the products, with some new products being inaccessible using their standard alkyne counterparts.

Recent advances in the synthesis of bridgehead (or ring-junction) nitrogen heterocycles via transition metal-catalyzed C–H bond activation and functionalization

An update on recent advances in the synthesis of bridgehead nitrogen fused heterocycles via transition metal-catalyzed C–H activation and functionalization is reported.

Copper-catalyzed synthesis of pyrazolo[5,1-a]isoquinoline derivatives from 2-gem-dipyrazolylvinylbromobenzenes

An efficient copper-catalyzed synthesis of pyrazolo[5,1-a]isoquinolines from 2-gem-dipyrazolylvinylbromobenzenes under mild conditions has been developed.

Hetero-bimetallic cooperative catalysis for the synthesis of heteroarenes

Review covering the synthesis of 5- and 6-membered as well as condensed heteroarenes, focussing on the combinations in cooperative catalytic systems in strategies used to achieve selectivity and also highlights the mode of action for the cooperative catalysis leading to the synthesis of commercially and biologically relevant heteroarenes.

Relay tricyclic Pd(ii)/Ag(i) catalysis: design of a four-component reaction driven by nitrene-transfer on isocyanide yields inhibitors of EGFR

A four-component reactions promoted by Pd(ii)/Ag(i) relay catalysis paved the way for the development of a new EGFR inhibitor.

Synthesis of pyrazolo[5,1-a]isoquinolines through copper-catalyzed regioselective bicyclization of N-propargylic sulfonylhydrazones

An expeditious strategy for the synthesis of pyrazolo[5,1-a]isoquinolines through copper(ii)-catalyzed regioselective bicyclization of N-propargylic sulfonylhydrazones has been developed.

Silver-catalysed reactions of alkynes: recent advances

Silver is a less expensive noble metal. Superior alkynophilicity due to π-coordination with the carbon-carbon triple bond makes silver salts ideal catalysts for alkyne-based organic reactions. This review highlights the progress in alkyne chemistry via silver catalysis primarily over the past five years (ca. 2010-2014). The discussion is developed in terms of the bond type formed with the acetylenic carbon (i.e., C-C, C-N, C-O, C-Halo, C-P and C-B). Compared with other coinage metals such as Au and Cu, silver catalysis is frequently observed to be unique. This critical review clearly indicates that silver catalysis provides a significant impetus to the rapid evolution of alkyne-based organic reactions, such as alkynylation, hydrofunctionalization, cycloaddition, cycloisomerization, and cascade reactions.

1,3-Dipolar cycloadditions of azomethine imines

Azomethine imines are considered 1,3-dipoles of the aza-allyl type which are transient intermediates and should be generated in situ but can also be stable and isolable compounds. They react with electron-rich and electron-poor olefins as well as with acetylenic compounds and allenoates mainly by a [3 + 2] cycloaddition but they can also take part in [3 + 3], [4 + 3], [3 + 2 + 2] and [5 + 3] with different dipolarophiles. These 1,3-dipolar cycloadditions (1,3-DC) can be performed not only under thermal or microwave conditions but also using metallo- and organocatalytic systems. In recent years enantiocatalyzed 1,3-dipolar cycloadditions have been extensively considered and applied to the synthesis of a great variety of dinitrogenated heterocycles with biological activity. Acyclic azomethine imines derived from mono and disubstituted hydrazones could be generated by prototropy under heating or by using Lewis or Brønsted acids to give, after [3 + 2] cycloadditions, pyrazolidines and pyrazolines. Cyclic azomethine imines, incorporating a C-N bond in a ring, such as isoquinolinium imides are the most widely used dipoles in normal and inverse-electron demand 1,3-DC allowing the synthesis of tetrahydro-, dihydro- and unsaturated pyrazolo[1,5-a]isoquinolines in racemic and enantioenriched forms with interesting biological activity. Pyridinium and quinolinium imides give the corresponding pyrazolopyridines and indazolo[3,2-a]isoquinolines, respectively. In the case of cyclic azomethine imines with an N-N bond incorporated into a ring, N-alkylidene-3-oxo-pyrazolidinium ylides are the most popular stable and isolated dipoles able to form dinitrogen-fused saturated and unsaturated pyrazolopyrazolones as racemic or enantiomerically enriched compounds present in many pharmaceuticals, agrochemicals and other useful chemicals.

Ni(0)–Cu(i): a powerful combo catalyst for simultaneous coupling and cleavage of the C–N bond with cyclization to valuable amide-based pyrroles and 4-pyridones

We demonstrate unprecedented Ni(0)–Cu(i) combo catalysis for sequential bond activated domino N–C/C–C coupled annulation with N–C bond cleavage to afford valuable amide-based polysubstituted pyrroles and 4-pyridones selectively from β-ketoanilides.

Substrate selective synthesis of pyrazolo[1,5-a]pyridines through [3 + 2] cycloaddition of N-aminopyridines and β-nitro styrenes

Synthesis of 2 or 3-(hetero)aryl pyrazolo[1,5-a]pyridines through [3 + 2] cycloaddition ofN-aminopyridine with β-nitrostyrenes followed byin situdenitration under metal-free and mild conditions are described.

Copper-mediated synthesis of pyrazolo[1,5-a]pyridines through oxidative linkage of C–C/N–N bonds

Copper-mediated synthesis of pyrazolo[1,5-a]pyridine-3-carboxylates through oxidative linkage of C–C and N–N bonds under mild reaction conditions with broad substrate scope is described.

Synthesis of 2-trifluoromethylpyrazolo[5,1-a]isoquinolines via silver triflate-catalyzed or electrophile-mediated one-pot tandem reaction

An efficient one-pot tandem cyclization/[3 + 2] cycloaddition reaction of N’-(2-alkynylbenzylidene)hydrazides with ethyl 4,4,4-trifluorobut-2-ynoate under silver triflate-catalyzed or electrophile-mediated conditions is described. Various trifluoromethylated pyrazolo[5,1-a]isoquinolines were afforded in moderate to excellent yield by this developed method.

Progress of the synthesis of condensed pyrazole derivatives (from 2010 to mid-2013)

Condensed pyrazole derivatives are important heterocyclic compounds due to their excellent biological activities and have been widely applied in pharmaceutical and agromedical fields. In recent years, numerous condensed pyrazole derivatives have been synthesized and advanced to clinic studies with various biological activities. In this review, we summarized the reported synthesis methods of condensed pyrazole derivatives from 2010 until now. All compounds are divided into three parts according to the rings connected to pyrazole-ring, i.e. [5, 5], [5,F 6], and [5, 7]-condensed pyrazole derivatives. The biological activities and applications in pharmaceutical fields are briefly introduced to offer an orientation for the design and synthesis of condensed pyrazole derivatives with good biological activities.

Palladium/norbornene-mediated tandem C-H amination/C-I alkenylation reaction of aryl iodides with secondary cyclic O-benzoyl hydroxylamines and activated terminal olefins

A novel palladium-catalyzed norbornene-mediated three-component reaction for the construction of ortho-alkenyl aromatic tertiary amines has been achieved, which represents a useful extension of the Catellani-type tandem ortho-selective CH amination transformations.

Silver(I)-catalyzed addition-cyclization of alkyne-functionalized azomethines

AgOTf can catalyze an addition-cyclization tandem between alkyne-azomethine and a nucleophile such as ketone, nitroalkane, water, and terminal alkyne to give a polycyclic amide via six-exo-trig selectivity.

'One-pot' synthesis of dihydrobenzo[4,5][1,3]oxazino[2,3-a] isoquinolines via a silver(I)-catalyzed cascade approach

An efficient approach for the synthesis of biologically interesting fused tetracyclic isoquinolines in high yields and with a broad substrate scope has been developed. The strategy features an AgNO₃ catalyzed ‘one-pot’ cascade process involving formation of two new C–N bonds and one new C–O bond.