Regio- and Enantioselective Allylic Cyanomethylation by Synergistic Rhodium and Silane Catalysis

Rh/silane-cocatalyzed regio- and enantioselctive allylic cyanomethylation with inert acetonitrile directly has been developed. Addition of a catalytic amount neutral silane reagent as an acetonitrile anion carrier is essential for the success of this reaction. The synthesis of mono- and bis-allylation products can be switched by adjusting the size of substituents on the silane, ligands, and temperature. Chiral homoallylic nitriles could be synthesized in above 20:1 branch/linear ratio, up to 98% yield and >99% ee.

Diastereoselective Direct Catalytic Asymmetric Mannich-Type Reactions of Alkylnitriles with a Ni(II)-Carbene Complex

Despite recent advances in reactions using alkylnitriles as carbon nucleophiles, diastereoselective direct catalytic asymmetric reactions, in which two consecutive chiral centers could be controlled, remain largely unexplored. Herein, we report the addition of alkylnitriles (such as propionitrile) to imines in the presence of a catalytic amount of a chiral pincer-type Ni-carbene complex and potassium 2,6-di-tert-butyl-4-methylphenoxide (KBHT). BHT and molecular sieves were used as additives to improve the yields, diastereoselectivity, and enantiomeric ratio up to >99%, 90:10 anti/syn, and 97.5:2.5 er, respectively. The Mannich adducts can be readily converted to the corresponding β-amino acids.

Nickel-Catalyzed C(sp3)-H Functionalization of Benzyl Nitriles: Direct Michael Addition to Terminal Vinyl Ketones

An efficient nickel(0)-catalyzed addition of benzyl nitriles to terminal vinyl ketones via C(sp³)-H functionalization has been developed. The reaction provides a novel and efficient protocol for the synthesis of α-functionalized benzyl nitriles with a wide range of structural diversity under mild reaction conditions while obviating the use of a strong base. The work might be potentially useful toward the development of an enantioselective variant using chiral nitrogen ligands.

Rational design of pincer-nickel complexes for catalytic cyanomethylation of benzaldehyde: A systematic DFT study

The current study dwells upon the efforts to computationally probe a phosphine-free pincer-nickel complex that would demonstrate an efficiency better than the reported phosphine-based pincer-nickel complex (^iPr2 POCN^Et2 )Ni(CH₂ CN) for cyanomethylation reaction. For this purpose, the mechanism of cyanomethylation of benzaldehyde was studied quantum mechanically for a series of 11 pincer-nickel complexes. The energetics of various intermediates and transition states involved in the catalytic cycle for each catalyst was compared with the corresponding energetics of the Miller's catalyst (^iPr2 POCN^Et2 )Ni(CH₂ CN) that is reported to accomplish the cyanomethylation at room temperature. While pincer complexes (^iPr4 NNN)Ni(CH₂ CN) and (^iPr4 NCN)Ni(CH₂ CN) containing strong σ-donating amines were found to fare poorly, pincer-nickel complexes (^iPr2 NCN)Ni(CH₂ CN) and (^dm PheboxNCN)Ni(CH₂ CN) based on weaker σ-donating imines had energetics more favorable than the reported efficient catalyst (^iPr2 POCN^Et2 )Ni(CH₂ CN). While strong trans-influencing C as the pincer central atom was found to be pivotal for lowering the cyanomethylation kinetics, presence of a poor trans-influencing N proved to be detrimental on the overall energetics.

Direct Catalytic Asymmetric Addition of Alkylnitriles to Aldehydes with Designed Nickel-Carbene Complexes

A direct catalytic asymmetric addition of acetonitrile to aldehydes that realizes over 90 % ee is the ultimate challenge in alkylnitrile addition chemistry. Herein, we report achieving high enantioselectivity by the strategic use of a sterically demanding Ni^II pincer carbene complex, which afforded highly enantioenriched β-hydroxynitriles. This highly atom-economical process paves the way for exploiting inexpensive acetonitrile as a promising C2 building block in a practical synthetic toolbox for asymmetric catalysis.

Asymmetric Transfer Hydrogenation of α-Substituted-β-Keto Carbonitriles via Dynamic Kinetic Resolution

A catalytic protocol for the enantio- and diastereoselective reduction of α-substituted-β-keto carbonitriles is described. The reaction involves a DKR-ATH process with the simultaneous construction of β-hydroxy carbonitrile scaffolds with two contiguous stereogenic centers. A wide range of α-substituted-β-keto carbonitriles were obtained in high yields (94%-98%) and excellent enantio- and diastereoselectivities (up to >99% ee, up to >99:1 dr). The origin of the diastereoselectivity was also rationalized by DFT calculations. Furthermore, this methodology offers rapid access to the pharmaceutical intermediates of Ipenoxazone and Tapentadol.

Cu-catalyzed cyanomethylation of imines and α,β-alkenes with acetonitrile and its derivatives

We describe copper-catalyzed cyanomethylation of imines and α,β-alkenes with a methylnitrile source and provide an efficient route to synthesize arylacrylonitriles and β,γ-unsaturated nitriles. This method tolerates aliphatic and aromatic alkenes substituted with a variety of functional groups such as F, Cl, Br, Me, OMe, tert-Bu, NO2, NH2 and CO2H with good to excellent yields (69-98%). These systems consist of inexpensive, simple copper catalyst and acetonitrile with its derivatives (α-bromo/α-iodo-acetonitrile) and are highly applicable in the industrial production of acrylonitriles.

Recent advances in pincer-nickel catalyzed reactions

Organometallic catalysts have played a key role in accomplishing numerous synthetically valuable organic transformations that are either otherwise not possible or inefficient. The use of precious, sparse and toxic 4d and 5d metals are an apparent downside of several such catalytic systems despite their immense success over the last several decades. The use of complexes containing Earth-abundant, inexpensive and less hazardous 3d metals, such as nickel, as catalysts for organic transformations has been an emerging field in recent times. In particular, the versatile nature of the corresponding pincer-metal complexes, which offers great control of their reactivity via countless variations, has garnered great interest among organometallic chemists who are looking for greener and cheaper alternatives. In this context, the current review attempts to provide a glimpse of recent developments in the chemistry of pincer-nickel catalyzed reactions. Notably, there have been examples of pincer-nickel catalyzed reactions involving two electron changes via purely organometallic mechanisms that are strikingly similar to those observed with heavier Pd and Pt analogues. On the other hand, there have been distinct differences where the pincer-nickel complexes catalyze single-electron radical reactions. The applicability of pincer-nickel complexes in catalyzing cross-coupling reactions, oxidation reactions, (de)hydrogenation reactions, dehydrogenative coupling, hydrosilylation, hydroboration, C-H activation and carbon dioxide functionalization has been reviewed here from synthesis and mechanistic points of view. The flurry of global pincer-nickel related activities offer promising avenues in catalyzing synthetically valuable organic transformations.

Copper-promoted cyanoalkylation/ring-expansion of vinylcyclopropanes with α-C-H bonds in alkylnitriles toward 3,4-dihydronaphthalenes

A copper-promoted oxidative cyanomethylation/ring-expansion of vinylcyclopropanes with α-C(sp3)-H bonds in alkyl nitriles is established for the generation of 1-cyanoethylated 3,4-dihydronaphthalenes. This cyanomethylation/ring-expansion involves a radical pathway and proceeds via cyanomethyl radical formation, radical addition and ring-expansion. This ring-expansion strategy offers a highly atom-economical route for the construction of nitrile-containing 3,4-dihydronaphthalenes, which can be transformed into other useful products under simple conditions.

Recent advances in C–CN and C–H bond activation of green nitrile (MeCN) for organo-complexation, cyanation and cyanomethylation

The use of green and inexpensive organic nitrile (MeCN) as a cyano and cyano-methyl source for organo-complexation, cyanation, and cyanomethylation is reviewed.

Cu2O-catalyzed selective 1,2-addition of acetonitrile to α,β-unsaturated aldehydes

A cyanomethylation of α,β-unsaturated aldehydes with acetonitrile as a nucleophile is disclosed. The reaction is promoted with Cu₂O as an inexpensive catalyst. Mild conditions are used, and the reaction completes within a few minutes.

Reductive C-C Coupling from α,β-Unsaturated Nitriles by Intercepting Keteniminates

We present an atom-economic strategy to catalytically generate and intercept nitrile anion equivalents using hydrogen transfer catalysis. Addition of α,β-unsaturated nitriles to a pincer-based Ru-H complex affords structurally characterized κ-N-coordinated keteniminates by selective 1,4-hydride transfer. When generated in situ under catalytic hydrogenation conditions, electrophilic addition to the keteniminate was achieved using anhydrides to provide α-cyanoacetates in high yields. This work represents a new application of hydrogen transfer catalysis using α,β-unsaturated nitriles for reductive C-C coupling reactions.

"On Water" Direct Organocatalytic Cyanoarylmethylation of Isatins for the Diastereoselective Synthesis of 3-Hydroxy-3-cyanomethyl Oxindoles

An "on water" organocatalytic cyanoarylmethylation of aryl acetonitrile to isatins is developed, giving products in high yields and up to excellent diastereoselectivities. A remarkable enhancement of reaction rates and diastereoselectivities by water was observed under mild conditions. Moreover, this approach provides a highly efficient and environmentally benign access to thermodynamic 3-hydroxy-3-cyanomethyl oxindoles.

Organocatalytic Decarboxylative Cyanomethylation of Difluoromethyl and Trifluoromethyl Ketones

An efficient organocatalytic method for the synthesis of difluoromethyl and trifluoromethyl substituted β-hydroxynitriles is introduced. The decarboxylative cyanomethylation of fluorinated ketones with readily available cyanoacetic acid gives a variety of tertiary alcohols in high yields and without concomitant water elimination. The reaction occurs in the presence of catalytic amounts of triethylamine, can be upscaled and applied to chlorofluoromethyl ketones and difluoromethyl ketimines.

Enantioselective synthesis of α,α-disubstituted α-amino acids via direct catalytic asymmetric addition of acetonitrile to α-iminoesters

Chiral N-heterocyclic carbene complexes of [Ir(cod)(OMe)]₂ in combination with Barton's base enabled direct enantioselective addition of acetonitrile to α-iminoesters.

An efficient aldol-type direct reaction of isatins with TMSCH2CN

Cesium fluoride catalyzed direct cyanomethylation of various isatins by using trimethylsilyl acetonitrile (TMSAN) as a nucleophile has been developed. The reaction has been explored for a number of isatins, with various substitutions on its aromatic ring. Further, the versatility of the reaction is demonstrated by converting the direct aldol adducts to various corresponding intermediates.

Covalent organic polymer framework with C–C bonds as a fluorescent probe for selective iron detection

Iron detection has just gone heterogeneous, thanks to the selective quenching of fluorescence by the nanoporous polymers that are tuned for optimal processability.

Direct coupling of nitriles and aniline to form the triazapentadiene species [upper bond 1 start]Rh(III){NH=C(R)N(Ph)C(R=N[upper bond 1 end]H}

The facile and high-yield reaction between aniline and cis-positioned nitriles of [((t)bpy)(2)Rh(NCR)(2)][OTf](3) [R = Me (2), Ph (3); (t)bpy = 4,4'-di-tert-butyl-2,2'-bipyridine; OTf = CF(3)SO(3)(-)] produces the Rh(III)-triazapentadiene species [((t)bpy)(2)[upper bond 1 start]Rh{NH=C(R)N(Ph)C(R=N[upper bond 1 end]H}][OTf](3) [R = Me (4), Ph (5)]. It represents the first example of direct coupling between two RCN ligands and a primary amine to form this type of metallacycle. X-ray structures of 2 and 4 are reported.