Oxidative Divergent Bicyclizations of 1,n-Enynes through α-C(sp3)-H Functionalization of Alkyl Nitriles

Diastereoselective Access to Ester-Substituted cis-Phenanthridinones via Hydrogen Atom Transfer-Involved 1,7-Enyne Bicyclization

An organophotoredox-catalyzed 1,7-enyne bicyclization for the cis-diastereoselective synthesis of ester-substituted phenanthridinones has been achieved through radical cascade cyclization involving 1,6-hydrogen atom transfer. This transition-metal- and oxidant-free one-pot protocol generates three distinct C-C bonds and two quaternary carbon centers.

Formation of cyclopenta[c]quinolines through visible-light-induced photoredox cascade bis-annulations of 1,7-enynes with sulfoxonium ylides

A novel visible-light-driven photoredox-catalyzed cascade bicyclization of 1,7-enynes with aqueous sulfoxonium ylides is reported. The reaction is highly chemoselective with three new C-C bonds, two new rings, and an all-carbon quaternary stereocenter constructed in a one-pot fashion. This mild protocol features a remarkably broad substrate scope with good functional group tolerance, providing a general and practical approach to access various cyclopenta[c]quinolines.

C-centered radical-initiated cyclization by directed C(sp3)–H oxidative functionalization

C(sp3)–H functionalization is attracting constant attention. This review emphasizes C-centered radicals initiated cyclization strategies by directed C(sp3)–H oxidative functionalization since 2012.

Cyanomethylative cyclization of unactivated alkenes with nitriles for the synthesis of cyano-containing ring-fused quinazolin-4(3H)-ones

The synthesis of cyano-containing pyrrolo- and piperidino-quinazolinones was developed using alkyl nitriles through radical cascade addition/cyclization under metal-free conditions.

Selective divergent radical cyclization of 1,6-dienes with alkyl nitriles

An efficient, selective, and step economical radical cyclization of 1,6-dienes with alkyl nitriles initiated by α-C(sp³)-H functionalization under the Sc(OTf)₃ and Ag₂CO₃ system is described here. The selective divergent cyclization relies on the substitution effect at the α-position of the acrylamide moiety and nitriles, which is terminated by hydrogen abstraction, direct cyclization with the aryl ring, or further cyclization with the CN bond and hydrolysis, respectively.

Copper/silver co-mediated three-component bicyclization for accessing indeno[1,2-c]azepine-3,6-diones

A new copper/silver-co-mediated three-component bicyclization of benzene-linked 1,6-enynes with ICF2CO2Et with TMSN3 was reported, and used to produce a wide range of hitherto unreported difluorinated tetrahydroindeno[1,2-c]azepine-3,6-diones with moderate to good yields. The mechanistic pathway consists of radical-induced 1,6-addition-cyclization, oxidative addition, reductive elimination, nitrene insertion and N-O cleavage, resulting in continuous multiple bond-forming events including C-C and C-N bonds to build up a 6/5/7 tricyclic framework.

Radical Tandem Bicyclization Triggered by the α-Position of α,β-Unsaturated Ketones Bearing Nonterminal 1,6-Enynes: Synthesis of the 5H-Benzo[a]fluoren-5-one Skeleton

A novel method for the synthesis of 5H-benzo[a]fluoren-5-one from inactive nonterminal 1,6-alkynes through a free radical tandem bicyclization process has been established. This process achieved a continuous cyclization triggered rarely by the α-position of α,β-unsaturated ketones. The reaction constructed three C-C bonds in one step with the readily accessible substrates and excellent substrate compatibility.

Cu/Ni-Catalyzed Cyanomethylation of Alkenes with Acetonitrile for the Synthesis of β,γ-Unsaturated Nitriles

We have developed a protocol for the Cu/Ni-catalyzed cyanomethylation of alkenes with acetonitrile for the synthesis of β,γ-unsaturated nitriles. This is the first example of a direct coupling of the alkene sp² C-H bond and the acetonitrile sp³ C-H bond for the preparation of β,γ-unsaturated nitriles. Acetonitrile, an inexpensive and stable solvent, is demonstrated to be a useful cyanomethyl source. The combination of copper and nickel catalysts resulted in a high reaction efficiency.

Cyanomethylation of Substituted Fluorenes and Oxindoles with Alkyl Nitriles

The first example of metal-free cyanomethylenation from alkyl nitriles of sp³ C-H bonds to afford quaternary carbon centers is described. This oxidative protocol is operationally simple and features good functional group compatibility. This method provides a novel approach to highly functionalized fluorene and oxindole derivatives, which are commonly used in material and pharmaceutical areas. Control experiments provide evidence of a radical reaction process.

Radical-mediated oxidative annulations of 1,n-enynes involving C–H functionalization

Recent progress in oxidative annulations of 1,n-enynes involving C–H functionalization is summarized.

Metal-Free Radical [2 + 2 + 1] Cyclization of ortho-Cyanoarylacrylamides with Alkyl Nitriles: Synthesis of Pyrrolo[3,2- c]quinolines

A novel radical [2 + 2 + 1] cyclization of ortho-cyanoarylacrylamides with dual α-C-H bonds in alkyl nitriles has been developed. The reaction provides new facile and straightforward access to cyano-substituted pyrrolo[3,2- c]quinolines, which are important nitrogen-containing polyheterocycles. A possible mechanism for the transformation is proposed.

Silver-mediated oxidative 1,2-alkylesterification of styrenes with nitriles and acids via C(sp3)–H functionalization

A new silver-mediated 1,2-alkylesterification of alkenes with nitriles and acids promoted by a catalytic amount of nickel catalyst for producing acyloxylated nitriles has been developed via a C(sp³)–H functionalization process.

Metal-free oxidative [2+2+1] heteroannulation of 1,7-enynes with thiocyanates toward thieno[3,4-c]quinolin-4(5H)-ones

A new metal-free oxidative [2+2+1] heteroannulation of 1,7-enynes with thiocyanates for producing thieno[3,4-c]quinolin-4(5H)-ones is presented. This reaction employs benzoylperoxide (BPO) as the oxidant and sodium thiocyanate as the sulfur source to enable the formation of three chemical bonds, two C-S bonds and one C-C bond, in a single reaction, and represents a new, practical access to S-heterocycles with the avoidance of the use of metal catalysts and excess bases.

Iron-catalyzed reductive cyclization reaction of 1,6-enynes for the synthesis of 3-acylbenzofurans and thiophenes

A facile synthesis of 3-acylbenzofurans and thiophenes via iron(ii)-catalyzed reductive cyclization of 1,6-enynes has been developed.

Synthesis of hybrid polycycles containing fused hydroxy benzofuran and 1H-indazoles via a domino cyclization reaction

A trifluoroacetic acid mediated [3+2] annulation reaction between 5-hydroxy-1H-indazoles – generated in situ – and p-benzoquinones has been reported.

Catalytic, metal-free alkylheteroarylation of alkenes via distal heteroaryl ipso-migration

A new direct alkylheteroarylation of alkenes with simple alkylnitriles via distal heteroaryl ipso-migration has been accomplished under metal-free conditions, in which inexpensive alkylnitriles served as radical precursors, which together with ease of operation makes this process a very practical protocol.

Oxidative three-component 1,2-alkylarylation of alkenes with alkyl nitriles and N-heteroarenes

Indium-promoted oxidative three-component 1,2-alkylarylation of alkenes with alkyl nitriles and N-heteroarenes is achieved by C(sp³)–H/C(sp²)–H functionalization.

Radical cascade cyclization of 1,n-enynes and diynes for the synthesis of carbocycles and heterocycles

This review highlights recent advances in radical cascade cyclization of 1,n-enynes and diynes for the construction of carbo- and heterocycles.

Diastereoselective building up polycyclic tetrahydrofurans via tandem annulation of 1,n-enynes with aliphatic acids

A silver-catalyzed tandem annulation of aniline-linked 1,7-enynes with aliphatic acids has been reported. These synergistic tandem annulations allowed for the straightforward and efficient synthesis of various highly diastereoselective polycyclic tetrahydrofurans.

Palladium-catalyzed dearomatizative [2 + 2 + 1] carboannulation of 1,7-enynes with aryl diazonium salts and H2O: facile synthesis of spirocyclohexadienone-fused cyclopenta[c]quinolin-4(5H)-ones

The first 1,7-enyne dearomatizative [2 + 2 + 1] carboannulation using aryl diazonium salts as the one-carbon units is described.