Silver(I)-Mediated Phosphorylation/Cyclization Cascade of N-Cyanamide Alkenes for Divergent Access to Quinazolinones and Dihydroisoquinolinones

Visible-light promoted radical cascade cyclization of 3-allyl-2-arylquinazolinones for the synthesis of phosphorylated dihydroisoquinolino[1,2-b]quinazolinones

A novel visible-light promoted metal-free radical cascade cyclization reaction has been developed with 3-allyl-2-arylquinazolinones as a new class of radical acceptor. This photocatalytic protocol represents an efficient approach to construct phosphorylated dihydroisoquinolino[1,2-b]quinazolinones featuring mild conditions, broad substrate scope, and gram-scale synthesis.

Cu2O-catalyzed cascade phosphinylation/cyclization of 2'-aminochalcones for the synthesis of hemi-indigo derivatives

A Cu2O-catalyzed cascade phosphinylation/cyclization reaction of 2'-aminochalcones and diphenylphosphine oxides to produce hemi-indigo derivatives has been developed. This strategy facilitates the sequential formation of a C-P bonds and a C-N bond in a single reaction step. Notably, the approach features one-pot operation, an earth-abundant copper catalyst, readily available starting materials, a broad substrate scope and high compatibility with functional groups, providing 33 compounds in acceptable yields.

Access to N-Fused Quinazolinones by Radical-Promoted Cascade Annulations of Alkenyl N-Cyanamides with Aromatic Aldehydes

A cascade radical cyclization of alkenyl N-cyanamides with aromatic aldehydes has been achieved for an expeditious synthesis of keto-methylated dihydropyrrolo-quinazolinones. Benzoyl radicals, generated from aryl aldehydes in the presence of di-tert-butyl peroxide (DTBP), promoted the domino annulations leading to distinctive functionalized quinazolinones in good yields. In addition, the robustness of the present protocol is validated by employing heterocyclic and natural product-based aldehydes.

Visible-Light-Promoted Radical Cascade Cyclization of 2-Vinyl Benzimidazoles: Access to Benzo[4,5]imidazo[1,2-b]isoquinolin- 11(6H)-ones

A visible-light-enabled photoredox radical cascade cyclization of 2-vinyl benzimidazole derivatives is developed. This chemistry is applicable to a wide range of N-aroyl 2-vinyl benzimidazoles as acceptors, and halo compounds, including alkyl halides, acyl chlorides and sulfonyl chlorides, as radical precursors. The Langlois reagent also serves as an effective partner in this photocatalytic oxidative cascade process. This protocol provides a robust alternative for rendering highly functionalized benzo[4,5]imidazo[1,2-b]isoquinolin-11(6H)-ones.

Access to CF2COR-Containing Quinazolinones via Visible-Light-Induced Domino Difluoroalkylation/Cyclization of N-Cyanamide Alkenes

A green and highly efficient visible-light-induced radical cascade difluoroalkylation/cyclization reaction of N-cyanamide alkenes has been developed. A variety of CF2COR-containing quinazolinones have been obtained in high yields with cheap non-metallic 4CzIPN as the photocatalyst. This photocatalytic reaction provides rapid, facile, and practical access to valuable polycyclic quinazolinone, and it is amenable to the gram scale.

Photocatalytic cyclization of 3-(2-isocyanophenyl)quinazolin-4(3H)-ones for the construction of quinoxalino[2,1-b]quinazolinones

A new kind of building unit, 3-(2-isocyanophenyl)quinazolin-4(3H)-ones, was designed and synthesized for the construction of novel quinoxalino[2,1-b]quinazolinones. The radical cyclization of 3-(2-isocyanophenyl)quinazolin-4(3H)-ones with ethers afforded ether-substituted tetracyclic quinoxalino[2,1-b]quinazolinones under photocatalytic and metal-free conditions. In the process, the isocyano accepts a carbon radical to give an imidoyl radical, which adds to the electron-deficient CN bond in quinazolin-4(3H)-one.

Oxidative cascade cyclization of N-arylacrylamides with TMSN3

An azido-radical-triggered cyclization of N-(o-cyanobiaryl)acrylamides with TMSN3via a C(sp3)-N/C(sp2)-C(sp3)/C(sp2)-N bond formation cascade is described. This reaction features mild conditions and high bond-forming efficiency, making it an efficient method for the construction of azide-substituted pyridophenanthridines.

Base-Mediated and Silver-Catalyzed Divergent Synthesis of Hydroxynaphthalenamides and Phosphorylated Dihydronaphthylamides from Enone-Oxazolones

An efficient divergent approach to functionalized naphthalene derivatives, the naphthalenamides, via base-mediated and silver-catalyzed cyclization has been developed using enone-oxazolones as the precursors. This protocol utilized base in methanol with heating to construct the corresponding hydroxynaphthalenamides 2 by a C-C bond formation, oxazolone ring-opening, and aromatization in good yields. On the other hand, phosphorylated dihydronaphthylamides 3 were generated by using H-phosphonate as the phosphonating reagent in a silver-catalyzed cyclization involving the phospha-1,4-addition/intramolecular ring closure with concomitant C-P/C-C bond formation in good yields.

Visible-Light-Promoted Cascade Cyclization of 3-Ethynyl-[1,1'-biphenyl]-2-Carbonitriles with Unsaturated α-Bromocarbonyls

A visible-light-promoted cascade cyclization of 3-ethynyl-[1,1'-biphenyl]-2-carbonitriles with unsaturated α-bromocarbonyls for the synthesis of tetrahydrobenzo[mn]cyclopenta[b]acridines is described. Three C(sp3)-C(sp2) bonds, one C(sp2)-N bond, and three cycles can be formed in a single reaction through the addition of a C-centered radical to the carbon-carbon triple bond and three radical cyclizations. This reaction features mild conditions, wide substrate scope, and high bond-forming efficiency.

Structure and Additive-free Transamidation of Planar N-Cyano Amides

Although transamidation of amides generally requires metals, additives, or harsh conditions, we present here a facile transamidation of N-cyano amides with various amines at ambient temperature without any additive. N-cyano amides preferred the trans conformation and have a reduced double bond character revealed by crystal analysis. The DFT study indicates that the transamidation reaction proceeds through the direct attack of amine on the amide carbonyl since the LUMO (or LUMO+1) is located at the carbonyl moiety.

Metal-Free Photoinduced Hydrocyclization of Unactivated Alkenes toward Ring-Fused Quinazolin-4(3H)-ones via Intermolecular Hydrogen Atom Transfer

A visible-light-induced hydrocyclization of unactivated alkenes was developed using 3CzClIPN as the photocatalyst to generate substituted α-methyldeoxyvasicinones and α-methylmackinazolinones in moderate to good yields. An intermolecular hydrogen atom transfer with THF as the hydrogen source was involved. Mechanism studies indicated that the intramolecular addition of the in situ formed aminal radical to the unactivated alkene generated the polycyclic quinazolinone.

Metal- and Base-Free Radical Cascade Cyclization/Hydrolysis of CN-Containing 1,6-Enynes with Ethers to Access Polyheterocycles

A convenient and straightforward approach for the radical cascade cyclization/hydrolysis of CN-containing 1,6-enynes with simple ethers under metal- and base-free conditions is described. This strategy provides a variety of valuable ethers-substituted polyheterocycles via the construction of three C-C bonds, one C=O bond, and two new six-membered rings within a single procedure. The resulting products can smoothly undergo follow-up conversions to various useful scaffolds. The methodology shows excellent functional group tolerance, high step- and atom- economy, and mild reaction conditions, which can be further scaled up to gram quantity in a satisfactory yield.

Synthesis of Trifluoromethylated γ-Lactams through Radical Cascades of N-Cyano Alkenes with CF3SO2Na

We report herein a facile strategy to synthesize trifluoromethylated γ-lactams through trifluoromethylcarbonylation of N-cyano alkenes using readily available CF₃SO₂Na as the CF₃ radical source. A range of trifluoromethyl-containing γ-lactams was obtained in good yields. This transition-metal-free protocol is demonstrated with mild conditions, broad substrate scope, good functional group tolerance, convenient reagents, and an easy-to-handle operating system.

The Renaissance of Organo Nitriles in Organic Synthesis

In the arena of functional group-oriented organic synthesis, the nitrile or cyano functionality is of immense importance. The presence of nucleophilic N -atom, π-coordinating ability of the triple bond, and electrophilic C-center imparts unique and interesting reactivity. Owing to the ability of the nitrile to transform into various other functional groups or intermediates, the chemistry is very rich and diverse. In particular, the involvement of nitrile in numerous organic reactions such as inter- or intramolecular alkyne insertion, [2 + 2 + 2] cycloaddition with alkynes, [3 + 2] cycloaddition with azides, [4 + 2] cycloaddition with diene allow the synthesis of many important carbocycles and heterocycles. Furthermore, the nitrile serves as a directing group in many C-H bond functionalization reactions to introduce diverse functionality and participate as a radical acceptor in radical cascade strategies to obtain a large variety of functional molecules. This review mainly focuses on the reactivity and diverse synthetic application of the nitrile including C-H bond functionalization, alkyne insertion, cycloaddition, and thermal or photochemical cascade strategy. The objective of the current review aims at bringing out the striking collection of various nitrile-triggered organic transformations.

Access to Phosphine-Containing Quinazolinones Enabled by Photo-Induced Radical Phosphorylation/Cyclization of Unactivated Alkenes

A mild and facile photo-induced cascade radical addition/cyclization of unactivated alkenes has been reported, through which a variety of biologically valuable phosphine-containing quinazolinones could be obtained in moderate to good yields. The protocol was characterized by mild conditions, broad substrate scope, and high atomic economy.

Facile One-Pot Synthesis of Functionalized Quinoline-Fused Fluorescent Dihydro/Spiro-quinazolinone Derivatives

A facile and efficient method has been developed for the synthesis of quinoline-fused fluorescent dihydro/spiro-quinazolinones. A plausible mechanism involving an acid-mediated enaminone intermediate is provided. The reaction proceeded using p-toluene sulfonic acid as a green promoter. The methodology was successful in synthesizing various quinoline-appended spiro-quinazolinones 4a-o. The synthetic utility of compounds 4a-o was demonstrated by synthesizing compounds 6a-d via Suzuki coupling as a key reaction. Significantly, the π-π* electronic transition of compounds 4c and 4k showed a blue shift. The molar extinction coefficient (ε), Stoke's shift (Δu̅), and quantum yield (Φ^f)_c were calculated for these derivatives (4c and 4k).

Palladium-catalyzed radical cascade cyanoalkylsulfonylation/cyclization of 3-arylethynyl-[1,1'-biphenyl]-2-carbonitriles with cyclobutanone oxime esters and DABSO

A palladium-catalyzed radical cascade cyanoalkylsulfonylation/cyclization of 3-arylethynyl-[1,1'-biphenyl]-2-carbonitriles with DABCO·(SO₂)₂ and cyclobutanone oxime esters via cleavage of a C-C single bond and insertion of SO₂ was described. A series of cyanoalkylsulfone-containing cyclopenta[gh]phenanthridines were obtained in moderate-to-good yields, thus featuring mild reaction conditions, a broad substrate scope, and a high functional group tolerance.

A Photosensitizer-Free Radical Cascade for Synthesizing CF3-Containing Polycyclic Quinazolinones with Visible Light

Herein, we report an efficient photoinduced radical tandem trifluoromethylation/cyclization reaction of N-cyanamide alkenes for the synthesis of functionalized quinazolinones. Importantly, the reaction is carried out under mild conditions without any additional photosensitizer, metal, or extra additives. A series of trifluoromethyl quinazolinones were prepared efficiently with good yields and excellent functional group tolerance. Preliminary mechanistic experiments were conducted to indicate that the transformation proceeds via a possible mechanism involving photoexcited EDA complex and chain propagation.

Highly Regioselective Tandem Reaction of Ene-Yne-Oxazolones Induced by H-Phosphonates: Construction of Phosphinylindane Derivatives

A highly regioselective divergent approach for the phosphine-containing indane/indene derivatives from the ene-yne-oxazolone precursors was reported. An insight into the reaction mechanism involving the phospha-1,4-addition followed by 5-exo-dig ring closure with a concomitant C-P/C-C bond formation was also proposed. This promising protocol utilized H-phosphonate as the phosphonating reagent in a silver-catalyzed or base-mediated cascade cyclization to construct the corresponding phosphorylated spiroindenoxazolones and amidoindenes, respectively, in good yields (up to 88% yield).

Nitriles as radical acceptors in radical cascade reactions

The application of the cyano group as a radical acceptor in the cascade reactions for the construction of various important heterocycles and carbocycles was summarized.

Catalysis and regioselectivity in hydrofunctionalization reactions of unsaturated carbon bonds. Part III

The review addresses the possibility of obtaining Markovnikov and anti-Markovnikov isomers in the reactions of unsaturated hydrocarbons with organophosphorus and organosulfur compounds having P–H and S–H bonds using metal salts or complexes as catalysts.

The bibliography includes 247 references.

Efficient synthesis of SCF3-substituted tryptanthrins by a radical tandem cyclization

Herein, we report a new, efficient and atom-economical strategy for the synthesis of SCF₃-substituted tryptanthrin derivatives. These previously unreported derivatives were obtained by means of a radical tandem cyclization. The reaction was triggered by addition of a SCF₃ radical to a carbon-carbon double bond and involved the formation of a C(sp³)-SCF₃ bond, a C(sp²)-C bond, and a C(sp²)-N bond. This method has mild conditions and a wide range of substrates which is particularly useful for the preparation of substituted indolquinazoline derivatives that widely exist in many natural products, but are not easy to obtain by conventional approaches.

TBPB-initiated cascade cyclization of 3-arylethynyl-[1,1'-biphenyl]-2-carbonitriles with sulfinic acids: access to sulfone-containing cyclopenta[gh]phenanthridines

A novel TBPB-initiated cascade cyclization of 3-arylethynyl-[1,1'-biphenyl]-2-carbonitriles with sulfinic acids via C-S, C-C and C-N bond formation for the synthesis of 3-sulfonated cyclopenta[gh]phenanthridines under metal-free conditions has been developed. This protocol features mild conditions, good functional group tolerance and a broad substrate scope. By using this protocol, a variety of potentially bioactive 3-sulfonated cyclopenta[gh]phenanthridines were facilely synthesized via direct annulation.

Defluorinative C(sp3 )-P Bond Construction for the Synthesis of Phosphorylation gem-Difluoroalkenes under Catalyst- and Oxidant-Free Conditions

Defluorinative C(sp³ )-P bond formation of α-trifluoromethyl alkenes with phosphine oxides or phosphonates have been achieved under catalyst- and oxidant-free conditions, giving phosphorylation gem-difluoroalkenes as products. α-Trifluoromethyl alkenes bearing various of aryl substituents such as halogen, cyano, ester and heterocyclic groups are available in this transformation. The results of control experiments demonstrated that the mechanism of dehydrogenative/defluorinative cross-coupling reactions was not a radical route, but might be an S_N 2' process involving phosphine oxide anion.

Mn(III)-Mediated Cascade Cyclization of 3-Isocyano-[1,1'-biphenyl]-2-carbonitrile with Arylboronic Acid: Construction of Pyrrolopyridine Derivatives

A Mn(III) mediated cascade cyclization of new designed multifunctionalized 3-isocyano-[1,1'-biphenyl]-2-carbonitrile with arylboronic acid to construct pyrrolopyridine derivatives is developed. A series of pyrroloporidine compounds have been constructed through the formation of two new C-C bonds and one C-N bond via a radical pathway.

Regioselective radical arylation: silver-mediated synthesis of 3-phosphorylated coumarins, quinolin-2(1H)-one and benzophosphole oxides

A silver-mediated domino radical addition/cyclization reaction of diaryl- or dialkyl-phosphine oxides with propynoic acid derivatives delivering 3-phosphorylated coumarins, quinolin-2(1H)-one and benzophosphole oxides is presented.

Regioselective synthesis of polycyclic sulfones via radical-induced three-component bicyclization cascades

New radical-triggered three-component bicyclization cascades of 2-alkynylaryldiazonium tetrafluoroborates with a sulfur dioxide surrogate DABCO·(SO₂)₂ and internal alkynes have been reported for the first time, leading to 49 examples of polycyclic sulfones with moderate to good yields.

Silver-mediated radical phosphorylation/cyclization of N-allylbenzamides to access phosphoryl-substituted dihydroisoquinolones

A silver-mediated phosphorylation/cyclization of N-allylbenzamides with phosphine oxides for the synthesis of phosphoryl-substituted dihydroisoquinolones was developed.

Synthesis of Diverse Boron-Handled N-Heterocycles via Radical Borylative Cyclization of N-Allylcyanamides

A synthetic method based on radical borylation/cyclization cascades of N-allylcyanamides was developed to construct diverse boron-substituted N-heterocycles. In the reaction process, the N-heterocyclic carbene-boryl radical underwent a chemo- and regioselective addition to the alkene moiety, followed by cyclization with the N-cyano group. The resulting amide-iminyl radical intermediates underwent further reactions to afford various boron-tethered N-heterocyclic molecules. Further transformations to access synthetically useful building blocks were also demonstrated.