Approach to Access Benzo[j]phenanthridinones from 1,7-Enynes and Aryldiazonium Salts via a Domino Radical Relay Process Enabled by a P/N-Heteroleptic Cu(I)-Photosensitizer.

A mild approach for the synthesis of benzo[j]phenanthridin-6(5H)-one derivatives from 1,7-enynes and aryldiazonium salts has been successfully developed involving a domino radical relay process enabled by a heteroleptic Cu(I)-photosensitizer under visible-light-driven photocatalytic conditions. Mechanistic studies disclosed that the oxidative quenching of the excited state of PS 4 with aryldiazonium salts via an SET process generated aryl radicals, which could play a radical initiator-terminator dual role within the whole radical relay process, namely, at the initial step acting as a radical donor to trigger the radical addition to the olefin moieties of 1,7-enynes while at the final stage serving as a radical acceptor to complete the cyclization.

Aryl boronic acid-controlled divergent ring-contraction and ring-opening/isomerization reaction of tert-cyclobutanols enabled by nickel catalysis.

In this work, we wish to present a nickel-catalyzed divergent ring-contraction and ring-opening/isomerization reaction of tert-cyclobutanols. The key to control these two different reaction pathways is to choose appropriate boronic acid, where the use of phenylboronic acid and pyrimidin-5-ylboronic acid enables a ring-contraction and ring-opening reaction/isomerization, respectively. Both cyclopropyl aryl methanones and 1-aryl butan-1-ones could be selectively obtained.

Nickel-catalyzed divergent formylation and carboxylation of aryl halides with isocyanides.

Herein, we describe a nickel-catalyzed divergent formylation and carboxylation reaction of aryl halides with isocyanides. A rich array of aromatic aldehydes and carboxylic acids can be, respectively, accessed in moderate to good yields. Some sensitive functional groups such as hydroxyl, iodine, cyano, and indolyl are fairly tolerant of nickel catalysis. In the carboxylation reactions, the combination of isocyanide and H2O is first employed as a promising carbonyl surrogate instead of gaseous CO and CO2.

P/N-heteroleptic Cu(I)-photosensitizer-catalyzed domino radical relay annulation of 1,6-enynes with aryldiazonium salts.

A visible-light driven photocatalytic construction of benzo[b]fluorenones from 1,6-enynes and aryldiazonium salts has been achieved via a P/N-heteroleptic Cu(I)-photosensitizer-catalyzed domino radical relay annulation process. Preliminary mechanistic studies revealed that the aryl radicals in situ generated from aryldiazonium salts with the excited state of the Cu(I)-photosensitizer played a dual role of a radical initiator and a radical terminator in the concise construction of the highly fused benzo[b]fluorenone scaffold.

P/N-Heteroleptic Cu(I)-Photosensitizer-Catalyzed [3 + 2] Regiospecific Annulation of Aminocyclopropanes and Functionalized Alkynes.

We report here a regiospecific [3 + 2] annulation between aminocyclopropanes and various functionalized alkynes enabled by a P/N-heteroleptic Cu(I) photosensitizer under photoredox catalysis conditions. Thus, a divergent construction of 3-aminocyclopentene derivatives including methylsulfonyl-, arylsulfonyl-, chloro-, ester-, and trifluoromethyl-functionalized aminocyclopentenes could be achieved with advantages of high regioselectivity, broad substrate compatibility, and mild and environmentally benign reaction conditions.

Nickel-catalyzed cascade hydrosilylation/cyclization of 1,7-enynes leading to silyl-containing quinolinones.

We herein describe a nickel-catalyzed cascade hydrosilylation/cyclization reaction of 1,7-enynes with bulky triphenylsilane. A series of silyl-containing quinolinone derivatives are obtained in good to excellent yields under mild reaction conditions. This reaction also features excellent chemoselectivity, broad functional group tolerance, and gram-scale synthesis.

Nickel-catalyzed cyanation reaction of aryl/alkenyl halides with alkyl isocyanides.

We herein describe a nickel-catalyzed cyanation reaction of aryl/alkenyl halides with alkyl isocyanides. Both aryl/alkenyl iodines and bromides were found to be competent electrophiles that reacted with alkyl isocyanides, affording nitrile compounds in moderate to good yields. A range of functional groups including halogens as well as hydroxyl, formyl, and acetamino groups were fairly compatible with the nickel catalysis. This protocol featured broad functional group tolerance, simple reaction conditions, and gram-scale synthesis.

Nickel-Catalyzed Arylation/Alkenylation of tert-Cyclobutanols with Aryl/Alkenyl Triflates via a C-C Bond Cleavage.

Herein, we first present a nickel-catalyzed arylation and alkenylation of tert-cyclobutanols with aryl/alkenyl triflates via a C-C bond cleavage. An array of γ-substituted ketones was obtained in moderate-to-good yields, thus featuring earth-abundant nickel catalysis, broad substrate scope, and simple reaction conditions. Preliminary mechanistic experiments indicated that ß-carbon elimination pathways might be involved in the catalytic cycle.

Nickel-catalyzed remote hydrosilylation of unconjugated enones with bulky triphenylsilane.

Herein we describe a nickel-catalyzed remote hydrosilylation of unconjugated enones with bulky triphenylsilane. A range of Z-silyl enol ethers are obtained as major isomers due to the process of nickel triggered alkene isomerization. Notably, some specific alkyl silyl enol ethers can be prepared from this protocol, which are not easily accessed by the traditional strategy using a strong base and chlorosilane. This reaction features 100% atom economy, simple reaction conditions, and good yields.

NHC-catalyzed Truce-Smiles rearrangement of N-aryl methacrylamides for the synthesis of trans-cinnamides.

Herein we describe a NHC-catalyzed Truce-Smiles rearrangement of N-aryl methacrylamides which enables the cleavage of an inert aryl C-N bond. A range of trans-cinnamides could be obtained by the direct construction of a C(aryl)-C(alkenyl) bond and functional groups such as Br, Cl, CN, and pyridinyl are compatible with NHC catalysis. The reaction features high atom-economy, transition-metal free catalysis, and easily available substrates.

Bifunctional Phosphine Ligand-Enabled Gold(I)-Catalyzed O-Nucleophilic Addition of N-Hydroxybenzo[1,2,3]-triazin-4(3H)-ones to Alkynes Followed by [3,3]-Rearrangement: Simultaneous Formation of C-O and C-N Bonds.

We describe a gold (I)-catalyzed tandem O-nucleophilic addition/[3,3]-rearrangement reaction of N-hydroxybenzo[1,2,3]-triazin-4(3H)-ones with alkynes enabled by a biphenyl-2-yl phosphine ligand featuring a pendant amide moiety (L1). A variety of 1-(2-oxo-2-arylethyl)benzo [d][1,2,3]triazin-4(1H)-one derivatives were synthesized in good to excellent yields. The present protocol gives a rare example of simultaneous formation of C-O and C-N bonds in the gold(I)-catalyzed [3,3]-sigmatropic rearrangements.

Diboron-Assisted Copper-Catalyzed Z-Selective Semihydrogenation of Alkynes Using Ethanol as a Hydrogen Donor.

We herein describe a B2Pin2-assisted copper-catalyzed semihydrogenation of alkynes. A variety of alkenes were obtained in good to excellent yields with Z-selectivity under mild reaction conditions. Mechanistic studies indicated that a transfer hydrogenation process was involved and ethanol acted as both a solvent and a hydrogen donor in this reaction. The present protocol enabled convenient synthesis of deuterium-substituted Z-alkenes such as Z-Combretastain A4- d2 in a high deuteration ratio by using readily available ethanol- d1 as the deuterium source.

I2O5-Mediated 1,5-Cyclization of Aryldiynes with H2O: A Way To Access 3-Acyl-1-indenone Derivatives.

A facile I2O5-mediated 1,5-cyclization of aryldiynes with H2O has been successfully developed, leading to a broad range of substituted 3-acyl-1-indenones in moderate to excellent yields. The protocol has advantages of a metal-free process, mild reaction conditions, simple operation, and broad functional group tolerance. In the reaction, H2O is used as both a cosolvent and an oxygen source.

I2O5-Mediated Iodocyclization Cascade of N-(1-Arylallyl)pyridine-2-amines with Concomitant C═C Bond Cleavage: A Synthesis of 3-Iodoimidazo[1,2- a]pyridines.

A facile method for the synthesis of 3-iodoimidazo[1,2- a]pyridines has been successfully developed involving an I2O5-mediated iodocyclization cascade of N-(1-arylallyl)pyridin-2-amines with concomitant C═C bond cleavage. Preliminary mechanistic studies reveal that this protocol might undergo an oxidative cyclization/decarboxylation/iodination sequence in which I2O5 is used as both an oxidant and an iodine source. The present protocol has advantages of wide substrate scope, simple operation, and metal-free conditions.

Copper-catalyzed three-component reaction of N-heteroaryl aldehydes, nitriles, and water.

An efficient and straightforward method for the synthesis of N-heteroaroyl imides has been successfully developed involving a copper-catalyzed radical-triggered three-component reaction of N-heteroaryl aldehydes, nitriles, and water. Mechanistic studies indicate that the reaction may undergo a radical-triggered Ritter-type reaction in which water serves as the oxygen source for the formation of the C-O bond. The reaction has advantages such as a broad substrate scope for the N-heteroaryl aldehydes, atom economy, and simple operation.

Copper(0)/Selectfluor System-Promoted Oxidative Carbon-Carbon Bond Cleavage/Annulation of o-Aryl Chalcones: An Unexpected Synthesis of 9,10-Phenanthraquinone Derivatives.

A general and efficient protocol for the synthesis of 9,10-phenanthraquinone derivatives has been successfully developed involving a copper(0)/Selectfluor system-promoted oxidative carbon-carbon bond cleavage/annulation of o-aryl chalcones. A variety of substituted 9,10-phenanthraquinones were synthesized in moderate to good yields under mild reaction conditions.

Palladium-Catalyzed sp(3) C-H Nitration of 8-Methylquinolines.

Palladium-catalyzed nitration of 8-methylquinolines with t-BuONO to give 8-(nitromethyl)quinolines in moderate to excellent yields has been developed involving an sp(3) C-H bond activation. The resulting (nitromethyl)quinolines could be selectively reduced to (1,2,3,4-tetrahydroquinolin-8-yl)methanamines by NaBH4 in the presence of a catalytic amount of NiCl2·6H2O.

Selectfluor-Mediated Simultaneous Cleavage of C-O and C-C Bonds in α,ß-Epoxy Ketones Under Transition-Metal-Free Conditions: A Route to 1,2-Diketones.

Selectfluor-mediated simultaneous cleavage of C-O and C-C bonds in α,ß-epoxy ketones has been successfully achieved under transition-metal-free conditions. The reaction gives 1,2-diketone compounds in moderate to good yields involving a ring-opening/benzoyl rearrangement/C-C bond cleavage sequence under oxidative conditions.

Palladium-catalyzed aromatic C-H bond nitration using removable directing groups: regiospecific synthesis of substituted o-nitrophenols from related phenols.

A general and regiospecific transformation of substituted phenols into the related o-nitrophenols has been achieved via a three-step process involving the palladium-catalyzed chelation-assisted ortho-C-H bond nitration as the key step. In the process, 2-pyridinyloxy groups act as removable directing groups for the palladium-catalyzed ortho-nitration of substituted 2-phenoxypridines, and they can be readily removed in the subsequent conversion of the resulting 2-(2-nitrophenoxy)pyridines into 2-nitrophenols.

Copper-catalyzed oxidative cyclization of 1,5-enynes with concomitant C-C bond cleavage: an unexpected access to 3-formyl-1-indenone derivatives.

A Cu(0)/Selectfluor system-mediated oxidative cyclization of 1,5-enynes with concomitant C-C bond cleavage to access 3-formyl-1-indenone derivatives is described. Preliminary mechanistic investigations disclosed that the C-C bond cleavage involved a novel water-participated oxygen-insertion ß-carbon elimination through double oxycuprations.