Copper-Catalyzed Umpolung of Imines through Carbon-to-Nitrogen Boryl Migration

Vinylidene rearrangements of internal borylalkynes via 1,2-boryl migration

Vinylidene rearrangement of alkynes is a well-established and powerful method for alkyne transformations, while use of borylalkynes has remained largely unexplored. This paper describes vinylidene rearrangements of internal borylalkynes using a cationic ruthenium complex. This rearrangement is applicable to alkynes with both tri-(B(pin), B(dan)) and tetracoordinate (B(mida)) boryl groups, and the reaction rate is dramatically affected by the Lewis acidity of the boryl group. Mechanistic study revealed that the rearrangement proceeds via 1,2-boryl migration regardless of the coordination number of the boron center. The migration mode was elucidated by theoretical calculations to indicate that the migration of the tricoordinate boryl groups is an electrophilic process in contrast to the previous vinylidene rearrangements of internal alkynes with two carbon substituents.

Synthesis of Homoallylamines Enabled by Cobalt or Palladium Catalyzed Allylic Substitution of Azaarylmethylamines

Pd(OAc)2/Nixantphos or CoI2/Nixantphos catalyzed allylic substitutions with weakly acidic C(sp)3-H bonds of azaarylmethylamines are described. This method facilitates access to various kinds of heteroaryl rings containing homoallylamines (39 examples, 30-98% yields) with excellent functional group tolerance and diastereoselectivity. Compared with the Pd/Nixantphos complex, the Co/Nixantphos catalysis could obtain the cyclic products with good to excellent diastereoselectivities. Importantly, the CoI2/(R,R)-Me-Duphos catalyzed reactions exhibit moderate enantioselectivity. Additionally, the scalability of this transformation is successfully demonstrated.

Remote 1,4-Carbon-to-Carbon Boryl Migration: From a Mechanistic Challenge to a Valuable Synthetic Application of Bicycles

The present paper reports a remote carbon-to-carbon boryl migration via an intramolecular 1,4-B/Cu shift, which establishes an in situ stereospecific electrophilic trap on the alkene moiety. The synthetic application is developed to prepare functionalized cyclopentenes by means of a palladium-catalyzed regioselective intramolecular coupling that completes a strategic cyclopropanation and generates valuable structural bicyclic systems. The mechanism is characterized by DFT (density functional theory) calculations which showed that the 1,4-migration proceeds through an intramolecular, nucleophilic attack of the copper-alkyl moiety on the boron atom bonded to the C(sp2), leading to a 5-membered boracycle structure. The computation of the 1,3- and 1,4-B/Cu shifts is also compared as is the impact of the endo- or exocyclic alkene on the reaction kinetics.

Acyclic Boryl Complexes of Copper(I)

Reaction of (6-Dipp)CuOtBu (6-Dipp=C{NDippCH2 }2 CH2 , Dipp=2,6-iPr2 C6 H3 ) with B2 (OMe)4 provided access to (6-Dipp)CuB(OMe)2 via σ-bond metathesis. (6-Dipp)CuB(OMe)2 was characterised by NMR spectroscopy and X-ray crystallography and shown to be a monomeric acyclic boryl of copper. (6-Dipp)CuB(OMe)2 reacted with ethylene and diphenylacetylene to provide insertion compounds into the Cu-B bond which were characterised by NMR spectroscopy in both cases and X-ray crystallography in the latter. It was also competent in the rapid catalytic deoxygenation of CO2 in the presence of excess B2 (OMe)4 . Alongside π-insertion, (6-Dipp)CuB(OMe)2 reacted with LiNMe2 to provide a salt metathesis reaction at boron, giving (6-Dipp)CuB(OMe)NMe2 , a second monomeric acyclic boryl, which also cuproborated diphenylacetylene. Computational interrogation validated these acyclic boryl species to be electronically similar to (6-Dipp)CuBpin.

Heterogeneous Single-Atom Zinc on Nitrogen-Doped Carbon Catalyzed Electrochemical Allylation of Imines

Organometallic reagents are effective for carbon-carbon bond formation; however, consumption of stoichiometric amounts of metals is problematic. We developed electrochemical allylation reactions of imines catalyzed by nitrogen-doped carbon-supported single-atom zinc, which were fixed on a cathode to afford a range of homoallylic amines efficiently. The system could suppress generation of metallic waste, and the catalyst electrode showed advantages over bulk zinc in terms of activity and robustness. An electrochemical flow reaction was also successfully performed to produce the homoallylic amine continuously with minimum amounts of waste.

Copper-Catalyzed Borylation of Acyl Chlorides with an Alkoxy Diboron Reagent: A Facile Route to Acylboron Compounds

Herein, the copper‐catalyzed borylation of readily available acyl chlorides with bis(pinacolato)diboron, (B₂pin₂) or bis(neopentane glycolato)diboron (B₂neop₂) is reported, which provides stable potassium acyltrifluoroborates (KATs) in good yields from the acylboronate esters. A variety of functional groups are tolerated under the mild reaction conditions (room temperature) and substrates containing different carbon‐skeletons, such as aryl, heteroaryl and primary, secondary, tertiary alkyl are applicable. Acyl N‐methyliminodiacetic acid (MIDA) boronates can also been accessed by modification of the workup procedures. This process is scalable and also amenable to the late‐stage conversion of carboxylic acid‐containing drugs into their acylboron analogues, which have been challenging to prepare previously. A catalytic mechanism is proposed based on in situ monitoring of the reaction between p‐toluoyl chloride and an NHC‐copper(I) boryl complex as well as the isolation of an unusual lithium acylBpinOBpin compound as a key intermediate.

Dinitrogen Cleavage and Functionalization with Carbon Dioxide in a Dititanium Dihydride Framework

The activation and functionalization of dinitrogen (N₂) with carbon dioxide (CO₂) are of great interest and importance but highly challenging. We report here for the first time the reaction of N₂ with CO₂ in a dititanium dihydride framework, which leads to N-C bond formation and N-N and C-O bond cleavage. Exposure of a dinitrogen dititanium hydride complex {[(^acriPNP)Ti]₂(μ₂-η¹:η²-N₂)(μ₂-H)₂} (1) (^acriPNP = 4,5-bis(diisopropylphosphino)-2,7,9,9-tetramethyl-9H-acridin-10-ide) to a CO₂ atmosphere at room temperature rapidly yielded a nitrido/N,N-dicarboxylamido complex {[(^acriPNP)Ti]₂(μ₂-N)[μ₂-N(CO₂)₂]} (2, 28%) and a diisocyanato/dioxo complex {[(^acriPNP)Ti]₂(NCO)₂(μ₂-O)₂} (3, 52%) with release of H₂. When the reaction of 1 with CO₂ (1 atm) was carried out at -50 °C, complex 2 was selectively formed in 82% yield within 5 min. Heating 2 at 80 °C under 1 atm CO₂ for 30 min afforded 3 in 67% yield. When 1 was allowed to react with 1.5 equiv of CO₂ at room temperature, an isocyanato/nitrido/oxo complex {[(^acriPNP)Ti]₂(NCO)(μ₂-N)(μ₂-O)} (4) was exclusively formed in 89% yield within 5 min. The reaction of 4 with CO₂ at room temperature almost quantitatively yielded the dioxo/diisocyanato complex 3 within 5 min. The mechanistic details were clarified by the ¹⁵N- and ¹³C-labeled experiments and density functional theory (DFT) calculations, providing unprecedented insights into the reaction of N₂ with CO₂. A titanium-mediated cycle for the synthesis of trimethylsilyl isocyanate Me₃SiNCO from N₂, CO₂, and Me₃SiCl using H₂ as a reducing agent was also established.

Unexpected chiral vicinal tetrasubstituted diamines via borylcopper-mediated homocoupling of isatin imines

Addressing the asymmetric synthesis of oxindole-based α-aminoboronic acids, instead of the expected products we disclosed the efficient homocoupling of oxindole-based N-tert-butanesulfinyl imines, with the generation of chiral, quaternary 1,2-diamines in a mild and completely stereoselective way. The obtained 3,3′-bisoxindole derivatives were fully characterized by NMR and single-crystal X-ray diffraction analysis and proved to be single diastereoisomers and atropisomers. A plausible mechanism for the one-pot Cu(II)-catalyzed Bpin addition to the isatin-derived ketimine substrate and subsequent homocoupling is described.

Challenges and recent advancements in the transformation of CO2 into carboxylic acids: straightforward assembly with homogeneous 3d metals

Transformation of carbon dioxide (CO2) into valuable organic carboxylic acids is essential for maintaining sustainability. In this review, such CO2 thermo-, photo- and electrochemical transformations under 3d-transition metal catalysis are described from 2017 until 2022.

First-Row d-Block Element-Catalyzed Carbon-Boron Bond Formation and Related Processes

Organoboron reagents represent a unique class of compounds because of their utility in modern synthetic organic chemistry, often affording unprecedented reactivity. The transformation of the carbon-boron bond into a carbon-X (X = C, N, and O) bond in a stereocontrolled fashion has become invaluable in medicinal chemistry, agrochemistry, and natural products chemistry as well as materials science. Over the past decade, first-row d-block transition metals have become increasingly widely used as catalysts for the formation of a carbon-boron bond, a transformation traditionally catalyzed by expensive precious metals. This recent focus on alternative transition metals has enabled growth in fundamental methods in organoboron chemistry. This review surveys the current state-of-the-art in the use of first-row d-block element-based catalysts for the formation of carbon-boron bonds.

Palladium catalyzed cascade umpolung allylation/acetalation for the construction of quaternary 3-amino oxindoles

Herein we reported a highly diastereoselective synthesis of quaternary 3-amino oxindoles bearing an acetal unit via a palladium catalyzed three-component cascade umpolung allylation/acetalation process. An array of 3-amino 3-allyl oxindoles incorporating diversified functional groups were prepared in good yields with exclusive diastereoselectivities. Further investigation demonstrated that the current method could also be extended to cascade umpolung allenylation/acetalation.

Transition-metal-free allylation of 2-azaallyls with allyl ethers through polar and radical mechanisms

Allylation of nucleophiles with highly reactive electrophiles like allyl halides can be conducted without metal catalysts. Less reactive electrophiles, such as allyl esters and carbonates, usually require a transition metal catalyst to facilitate the allylation. Herein, we report a unique transition-metal-free allylation strategy with allyl ether electrophiles. Reaction of a host of allyl ethers with 2-azaallyl anions delivers valuable homoallylic amine derivatives (up to 92%), which are significant in the pharmaceutical industry. Interestingly, no deprotonative isomerization or cyclization of the products were observed. The potential synthetic utility and ease of operation is demonstrated by a gram scale telescoped preparation of a homoallylic amine. In addition, mechanistic studies provide insight into these C(sp3)-C(sp3) bond-forming reactions.

Ambiphilic Al-Cu Bonding

Copper-alumanyl complexes, [LCu-Al(SiN^Dipp )], where L=carbene=NHC^iPr (N,N'-diisopropyl-4,5-dimethyl-2-ylidene) and ^Me2 CAAC (1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethyl-pyrrolidin-2-ylidene) and featuring unsupported Al-Cu bonds, have been prepared. Divergent reactivity observed with carbodiimides and CO₂ implies an ambiphilicity in the Cu-Al interaction that is dependent on the identity of the carbene co-ligand.

Ligand-Controlled Copper-Catalyzed Regiodivergent Carbonylative Synthesis of α-Amino Ketones and α-Boryl Amides from Imines and Alkyl Iodides

Regioselective transformation is among the long-standing challenges in organic synthesis. In this communication, a copper-catalyzed selectivity controlled regiodivergent borocarbonylation of imines with alkyl iodides has been developed. Various α-amino ketones and α-boryl amides were produced in moderate to good yields from the same substrates. The choice of the ligand is key for the regioselectivity control: α-amino ketones were produced selectively in good yields with (p-CF₃ C₆ H₄ )₃ P as the ligand, whereas the corresponding α-boryl amides were obtained with high regioselectivities when using ^Me IMes as the ligand.

Copper-catalyzed thioamination of maleimides with diethylphosphorodithioate and amines

The first copper-catalyzed oxidative aminophosphorothiolation of maleimides with secondary alkylamines and diethylphosphorodithioate has been established.

Nucleophilic reactivity of the gold atom in a diarylborylgold(i) complex toward polar multiple bonds

A di(o-tolyl)borylgold complex was synthesized via the metathesis reaction of a gold alkoxide with tetra(o-tolyl)diborane(4). The resulting diarylborylgold complex exhibited a Lewis acidic boron center and a characteristic visible absorption that arises from its HOMO–LUMO excitation, which is narrower than that of a previously reported dioxyborylgold complex. The diarylborylgold complex reacted with isocyanide in a stepwise fashion to afford single- and double-insertion products and a C–C coupled product. Reactions of this diarylborylgold complex with C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O/N double bond species furnished addition products under concomitant formation of Au–C and B–O/N bonds, which suggests nucleophilic reactivity of the gold metal center. DFT calculations provided details of the underlying reaction mechanism, which involves an initial coordination of the CO/N bond to the boron vacant p-orbital of the diarylboryl ligand followed by a migration of the gold atom from the tetracoordinate sp³-hybridized boron center, which is analogous to the reactivity of the conventional sp³-hybridized borate species. The DFT calculations also suggested a stepwise mechanism for the reaction of this diarylborylgold complex with isocyanide, which afforded three different reaction products depending on the applied reaction conditions.

A di(o-tolyl)borylgold complex added to CO/N double bond to form Au–C and B–O/N bonds. DFT calculations revealed a two-step mechanism consisting of the coordination of O/N atom to B atom followed by nucleophilic migration of Au atom.

Snapshots of magnesium-centred diborane heterolysis by an outer sphere SN2 process

Reactions of a magnesium diboranate as a source of [Bpin]^– anions are initiated by ‘outer sphere’ attack of C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> N bonded substrates.

Reactions of the β-diketiminato magnesium diboranate derivative, [(BDI)Mg{pinB(n-Bu)Bpin}] (BDI = HC{(Me)CNDipp}₂; Dipp = 2,6-i-Pr₂C₆H₃), with N,N′-dialkyl and N,N′-diaryl carbodiimides provided the corresponding C-borylated magnesium borylamidinates. This reactivity occurs with the displacement of n-BuBpin and with the apparent addition of a nucleophilic {Bpin} anion to the electrophilic unsaturated carbodiimide carbon centres. In contrast, while analogous reactions of [(BDI)Mg{pinB(n-Bu)Bpin}] with N-alkyl or N-aryl aldimines and ketimines also resulted in facile displacement of n-BuBpin, they provided the organomagnesium products of {Bpin} addition to the imine nitrogen atom rather than the more electrophilic trigonal imine carbon. Computational assessment by density functional theory (DFT) indicated that, although the energetic differences are marginal, the organomagnesium products may be considered as the kinetic outcome of these reactions with respect to the generation of alternative amidomagnesium regioisomers. This latter deduction was borne out by the thermally-induced conversion of two such organomagnesium species to their C-borylated amidomagnesium isomers, both of which occur with negligible entropies of activation indicative of purely intramolecular processes. Detailed analysis by DFT of the reaction of [(BDI)Mg{pinB(n-Bu)Bpin}] with PhN Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CHPh indicated that B–N bond formation is initiated by attack of the imine nitrogen at the three-coordinate boron atom of the diboranate anion rather than the more crowded magnesium centre. Consistent with an effectively spontaneous reaction, the resultant cleavage of the B–B bond of the diboranate unit is accomplished via the traversal of two very modest barriers of only 8.3 and 6.7 kcal mol^–1. This analysis was also supportive of a subsequent intramolecular B–N to B–C isomerisation process. Of greater general significance, however, the addition of the {Bpin}^– anion to the reducible aldimine is best rationalised as a consequence of the electrophilic character of this three-coordinate boron centre rather than any intrinsic nucleophilicity associated with the B–B bond of the [pinBB(n-Bu)pin]^– anion.