Copper-Mediated SN2′ Allyl–Alkyl and Allyl–Boryl Couplings of Vinyl Cyclic Carbonates

Copper-Catalyzed Regio-, Diastereo-, and Enantioselective Allylic Alkylation with 1,1-Diborylalkanes

We report a copper-catalyzed regio-, diastereo-, and enantioselective allylic alkylation of allyl bromides using 1,1-diborylalkanes as prochiral nucleophiles. This methodology employs copper(I) bromide as a catalyst, an (R)-BINOL-derived phosphoramidite as a ligand, and lithium benzoate as a crucial additive. The reaction affords enantioenriched homoallylic boronic esters possessing vicinal stereocenters in good yields and high diastereo- and enantioselectivity. The developed method demonstrates a broad substrate scope with respect to a wide range of 1,1-diborylalkanes and allyl bromides. Mechanistic studies, including deuterium-labeling experiments and DFT calculations, provide insights into the reaction pathway and the origin of the stereoselectivity. The synthetic utility of this method is showcased through various transformations of the obtained enantioenriched homoallylic boronic esters into valuable chiral building blocks.

Benzoxaborinine, New Chemotype for Carbonic Anhydrase Inhibition: Ex Novo Synthesis, Crystallography, In Silico Studies, and Anti-Melanoma Cell Line Activity

The benzoxaborinine scaffold, a homologue of benzoxaborole with an additional carbon atom in the boracycle, shows significant potential in developing new therapeutic agents. This study reports the synthesis, inhibition assays against four human carbonic anhydrase (hCA, EC 4.2.1.1) isoforms, and anti-melanoma evaluation of 7-aryl(thio)ureido-substituted benzoxaborinines. Some derivatives, particularly compound 11, exhibited potent inhibitory activity (below 65 nM) against hCA IX and XII and stronger antiproliferative effects than SLC-0111 on human melanoma cells under hypoxia. Crystallographic studies of benzoxaborinine 3 adducts with hCA I and II demonstrated the binding mode of this chemotype, revealing that although both benzoxaborinine 3 and benzoxaborole 10 share a similar zinc-binding mode, the expanded ring in benzoxaborinine led to a different orientation within the active site. These findings suggest that benzoxaborinines hold promise for designing novel carbonic anhydrase inhibitors.

Chemo-, Regio- and Stereoselective Preparation of (Z)-2-Butene-1,4-Diol Monoesters via Pd-Catalyzed Decarboxylative Acyloxylation

(Z)-alkenes are useful synthons but thermodynamically less stable than their (E)-isomers and typically more difficult to prepare. The synthesis of 1,4-hetero-bifunctionalized (Z)-alkenes is particularly challenging due to the inherent regio- and stereoselectivity issues. Herein we demonstrate a general, chemoselective and direct synthesis of (Z)-2-butene-1,4-diol monoesters. The protocol operates within a Pd-catalyzed decarboxylative acyloxylation regime involving vinyl ethylene carbonates (VECs) and various carboxylic acids as the reaction partners under mild and operationally attractive conditions. The newly developed process allows access to a structurally diverse pool of (Z)-2-butene-1,4-diol monoesters in good yields and with excellent regio- and stereoselectivity. Various synthetic transformations of the obtained (Z)-2-butene-1,4-diol monoesters demonstrate how these synthons are of great use to rapidly diversify the portfolio of these formal desymmetrized (Z)-alkenes.

Stereoselective Control of the Cu Activation of β,β-Diboryl Acrylates for Allylic Coupling Protocols with Concomitant Lactonization

The key to a successful C-B activation is to discriminate between two geminal boryl moieties that are exposed to the same reaction conditions. Here we describe a stereoselective C-B activation of β,β-diboryl acrylates forming exclusively the (Z)-α-borylalkenyl copper(I) key intermediate, for subsequent allylic alkylation reactions. The new borylated (Z)-skipped dienoates followed a feasible iodo-lactonization sequence for the preparation of borylated lactone cores, which can be used in drug discovery.

Vinyl and Alkynyl Substituted Heterocycles as Privileged Scaffolds in Transition Metal Promoted Stereoselective Synthesis

ConspectusBiologically active compounds and pharmaceutically relevant intermediates often feature sterically congested stereogenic centers, in particular, carbon stereocenters that are either tertiary tetrasubstituted ones or quaternary in nature. Synthons that comprise such bulky and often structurally complex core units are of high synthetic value and represent important incentives for communities connected to drug discovery and development. Streamlined approaches that give access to a diverse set of compounds incorporating acyclic bulky stereocenters are relatively limited, though vital. They enable further exploration of three-dimensional entities that can be designed and implemented in discovery programs, thereby extending the pool of molecular properties that is inaccessible for flat molecules. However, the lack of modular substrates in particular areas of chemical space inspired us to consider functionalized heterocycles known as cyclic carbonates and carbamates as a productive way to create sterically crowded alkenes and stereocenters.In this Account, we describe the major approximations we followed over the course of 8 years using transition metal (TM) catalysis as an instrument to control the stereochemical course of various allylic and propargylic substitution processes and related transformations. Allylic substitution reactions empowered by Pd-catalysis utilizing a variety of nucleophiles are discussed, with amination being the seed of all of this combined work. These procedures build on vinyl-substituted cyclic carbonates (VCCs) that are simple and easy-to-access precursors and highly modular in nature compared to synthetically limited vinyl oxiranes. Overall these decarboxylative conversions take place with either "linear" or "branched" regioselectivities that are ligand controlled and offer access to a wide scope of functional allylic scaffolds. Alternative approaches, including dual TM/photocatalyzed transformations, allowed us to expand the repertoire of challenging stereoselective conversions. This was achieved through key single-electron pathways and via formal umpolung of intermediates, resulting in new types of carbon-carbon bond formation reactions significantly expanding the scope of allylic substitution reactions.Heterocyclic substrate variants that have triple bond functional groups were also designed by us to enable difficult-to-promote stereoselective propargylic substitution reactions through TM catalysis. In these processes, inspired by the Nishibayashi laboratory and their seminal findings in the area, we discovered various new reactivity patterns. This provided access to a range of different stereodefined building blocks such as 1,2-diborylated 1,3-dienes and tetrasubstituted α-allenols under Cu- or Ni-catalysis. In this realm, the use of lactone-derived substrates gives access to elusive chiral γ-amino acids and lactams with high stereofidelity and good structural diversity.Apart from the synthetic efforts, we have elucidated some of the pertinent mechanistic manifolds operative in these transformations to better understand the limitations and opportunities with these specifically functionalized heterocycles that allowed us to create complex synthons. We combined both theoretical and experimental investigations that lead to several unexpected outcomes in terms of enantioinduction models, catalyst preactivation, and intermediates that are intimately connected to rationales for the observed selectivity profiles. The combined work we have communicated over the years offers insight into the unique reactivity of cyclic carbonates/carbamates acting as privileged precursors. It may inspire other members of the synthetic communities to widen the scope of precursors toward novel stereoselective transformations with added value in drug discovery and development in both academic and commercial settings.

α-Boryl Carbanions: The Influence of Geminal Heteroatoms in C-C Bond Formation

The wide applications of alpha-boryl carbanions in selective coupling with organohalides, imines/carbonyls and conjugated unsaturated substrates has become an interesting tool for organic synthesis. Strategically, the inclusion of heteroatoms, such as Si, S, N, F, Cl, Br and I in the alpha position opens a new venue towards multifunctionalities in molecular design. Here, a conceptual and practical view on powerful carbanions, containing α-silicoboron, α-thioboron, α-haloboron and α-aminoboron is given, as well as a prespective on their efficient application for selective electrophilic trapping.

Cu-Catalyzed Divergent Transformations of Allenylethylene Carbonates with Diboron Reagents

Divergent transformations of allenylethylene carbonates with diboron reagents catalyzed by copper are disclosed. By using CuCl/IPr·HCl as the catalyst, the allenylethylene carbonates react with B2hex2 to afford 2,4-dien-1-ols as the product in the presence of Cs2CO3 as the base, iPrOH as the additive, and 1,4-dioxane as the solvent. And they react with B2pin2 to form boronic half acids in the presence of NaOtBu as the base, water as the additive, and THF as the solvent. The reactions afford corresponding products in good stereoselectivities and yields, and further derivatizations of boronic half acids and study of the mechanism are also demonstrated.

Stereoselective Synthesis of Tri- and Tetrasubstituted Allylsilanes via Copper-Catalyzed Decarboxylative Silylation of Vinylethylene Carbonates

Herein, a stereoselective copper-catalyzed decarboxylative silylation of readily available vinylethylene carbonates (VECs) with PhMe2Si-Bpin is reported, affording a wide range of tri- and tetrasubstituted allylsilanes in moderate to high yields with E-selectivity. This protocol was characterized by high stereoselectivity, broad substrate scope, operational simplicity, and mild reaction conditions, which were amenable to diverse derivatizations and gram-scale synthesis.

Iso-Pentadienyl Carbonate as a Five Carbon Synthon in Manganese(I)-Catalyzed Selective Linear 1,3-Dienylation

Selective linear 1,3-dienylations are essential transformations, and numerous synthetic efforts have been documented. However, a general method enabling access to electron-rich, -poor, and biologically relevant dienyl molecules is in high demand. Hence, we report a straightforward method of manganese(I)-catalyzed C-H dienylation of arenes by using iso-pentadienyl carbonate as a five carbon synthon. This is a highly unprecedented report for selective linear 1,3-dienylation using manganese C-H activation catalysis. Our method facilitates the synthesis of varieties of dienes, including those suitable for normal or inverse electron demand Diels-Alder reactions, dienyl glycoconjugates, and unnatural amino acids. Extensive mechanistic studies, including isolation of C-H activated organo-manganese complex and isotopic analyses, have supported the proposed mechanism of this dienylation. The synthetic applicability of this method eased to deliver a 6/6/5-fused tricyclic nagilactone scaffold.

Palladium-catalyzed decarboxylative allylation of vinyloxazolidin-2-ones with sodium sulfinates: stereoselective assembly of highly functionalized (Z)-allylic amines

We report a general approach to highly functionalized (Z)-allylic amines by decarboxylative allylation of vinyloxazolidin-2-ones. This process engages sodium sulfinates as nucleophiles to form a new carbon-sulfur bond, utilizing a palladium catalyst generated from Pd(OAc)2 and diphosphine ligand dpppe. The scope of the protocol is illustrated by the synthesis of 30 representative allylic amines with high regio- and stereoselectivity. Mechanistic studies show that the Z-selectivity of the reaction stems from the formation of a palladacycle intermediate through Pd-N chelation. The synthetic utility of this method was further exemplified by the gram-scale synthesis and subsequent transformations to various compounds.

Organophosphorus-Catalyzed Borylative Ring-Opening of Vinylcyclopropanes: A Stereoselective Route to δ-Valerolactones

We report an operationally simple route to δ-valerolactones through an organophosphorus-catalyzed borylative ring-opening/allylation of vinylcyclopropanes providing δ-hydroxy esters stereoselectively. The δ-hydroxy esters were lactonized to obtain densely substituted δ-valerolactones. The present methodology exhibited enhanced functional group tolerance compared to the existing metal-mediated methods. A plausible mechanism for borylative ring-opening reaction has been suggested. ³¹P NMR studies indicated the involvement of a phosphonium zwitterionic species. The synthetic utility of the intermediate allyl boronates was demonstrated.

Palladium-Catalyzed Borylative Cyclizations of α-(2-Bromoaryl) Ketones to Form 1,2-Benzoxaborinines

Herein, we report that palladium catalyzes the borylative cyclization of α-(2-bromoaryl) ketones to afford 1,2-benzoxaborinines. The developed system is compatible with a variety of functionalities (Me, t-Bu, OMe, NMe₂, F, Cl, CN, CF₃, CO₂Me, and heteroaryl groups) and is applicable to the synthesis of B-O-containing tri- and tetracyclic fused-ring compounds.

Regio- and enantioselective formation of tetrazole-bearing quaternary stereocenters via palladium-catalyzed allylic amination

A general and efficient method via catalysis by readily available Pd(0)/DACH-naphthyl catalyst under mild conditions, unlocks a new platform that permits the synthesis of elusive quaternary N2-allylic tetrazoles, even in the context of late-stage functionalization.

Selective approach to N-substituted tertiary 2-pyridones

Commercially available 2-hydroxypyridines are converted into enantiomerically enriched allylic 2-pyridones with elusive N-substituted tertiary carbon by means of Pd-catalyzed allylic amination of vinyl cyclic carbonates.

Palladium-catalyzed stereoselective decarboxylative allylation of azlactones: access to (Z)-trisubstituted allylic amino acid derivatives

A palladium-catalyzed stereoselective decarboxylative allylation of azlactones with vinyl methylene cyclic carbonates affords a series of trisubstituted allylic amino acid derivatives in good yields with an exclusive (Z)-configuration.

Ligation of Boratabenzene and 9-Borataphenanthrene to Coinage Metals

The reactions of boratabenzene and borataphenanthrene anions with group 11 Ph₃PMCl reagents furnished η² coordination complexes, with the exception of the copper boratabenzene species that adopted an η⁶ mode. The binding of arene ligands to copper in an η⁶ manner is rare, and altering the ancillary ligand on copper to an N-heterocyclic carbene switched the binding of the boratabenzene to η², indicating that such ligands are capable of vacating coordination sites. The η² coordination complexes bind side-on, akin to olefins, via a borataalkene unit, although with the carbon atom much more proximal to the metal center than boron.

Pd/Cu Dual-Catalyzed Asymmetric Synthesis of Highly Functional All-Carbon Quaternary Stereocenters from Vinyl Carbonates

The challenging metal-catalyzed asymmetric synthesis of highly functional quaternary carbon centers using decarboxylative C(sp³ )-C(sp³ ) bond formation reactions is reported. The key substrate, a vinyl cyclic carbonate, is activated to provide concomitantly both the requisite nucleophile (by formal umpolung) and electrophile reaction partner preceding the asymmetric cross-coupling process. A wide screening of reaction conditions, additives and catalyst precursors afforded a protocol that gave access to a series of compounds featuring densely functionalized, elusive quaternary carbon stereocenters in appreciable yield and with enantiomeric ratios (er's) of up to 90 : 10.

Ni-Catalyzed Reductive Allylation of α-Chloroboronates to Access Homoallylic Boronates

The transition-metal-catalyzed allylation reaction is an efficient strategy for the construction of new carbon-carbon bonds alongside allyl or homoallylic functionalization. Herein we describe a Ni-catalyzed reductive allylation of α-chloroboronates to efficiently render the corresponding homoallylic boronates, which could be readily converted into valuable homoallylic alcohols or amines or 1,4-diboronates. This reaction features a broad substrate scope with good functional group compatibility that is complementary to the existing methods for the preparation of homoallylic boronates.

Five-Membered Cyclic Carbonates: Versatility for Applications in Organic Synthesis, Pharmaceutical, and Materials Sciences

This review presents the recent advances involving several applications of five-membered cyclic carbonates and derivatives. With more than 150 references, it covers the period from 2012 to 2020, with special emphasis on the use of five-membered cyclic carbonates as building blocks for organic synthesis and material elaboration. We demonstrate the application of cyclic carbonates in several important chemical transformations, such as decarboxylation, hydrogenation, and transesterification reactions, among others. The presence of cyclic carbonates in molecules with high biological potential is also displayed, together with the importance of these compounds in the preparation of materials such as urethanes, polyurethanes, and flame retardants.

Nickel-catalyzed asymmetric reductive aryl-allylation of unactivated alkenes

Herein we report a nickel-catalyzed asymmetric reductive aryl-allylation of aryl iodide-tethered unactivated alkenes, wherein both acyclic allyl carbonates and cyclic vinyl ethylene carbonates can serve as the coupling partners. Furthermore, the direct use of allylic alcohols as the electrophilic allyl source in this reaction is also viable in the presence of BOC anhydride. Remarkably, this reaction proceeds with high linear/branched-, E/Z- and enantio-selectivity, allowing the synthesis of various chiral indanes and dihydrobenzofurans (50 examples) containing a homoallyl-substituted quaternary stereocenter with high optical purity (90-98% ee). In this reductive reaction, the use of pregenerated organometallics can be circumvented, giving this process good functionality tolerance and high step-economy.

Copper-Mediated Dichotomic Borylation of Alkyne Carbonates: Stereoselective Access to (E)-1,2-Diborylated 1,3-Dienes versus Traceless Monoborylation Affording α-Hydroxyallenes

A mild copper-mediated protocol has been developed for borylation of alkynyl cyclic carbonates. Depending on the nature of the borylating reaction partner, either stereoselective diborylation of the propargylic surrogate takes place, providing convenient access to (E)-1,2-borylated 1,3-dienes, or traceless monoborylation occurs, which leads to α-hydroxyallenes as the principal product. The dichotomy in this borylation protocol has been scrutinized by several control experiments, illustrating that a relatively small change in the diboron(4) reagent allows for competitive alcohol-assisted protodemetalation to forge an α-hydroxyallene product under ambient conditions.

Palladium-catalyzed asymmetric allylic amination of a vinylethylene carbonate with N-heteroaromatics

Highly enantioselective allylic amination of a vinylethylene carbonate with N-heteroaromatics is enabled by asymmetric palladium catalysis for the synthesis of chiral acyclic nucleosides and isonucleosides.

Copper-catalyzed 1,6-conjugate addition of para-quinone methides with diborylmethane

Presented herein is the first 1,6-conjugate addition of diborylmethane. This reaction features high yields, mild reaction conditions, and broad functional group compatibilities.

Palladium-Catalyzed Regio- and Stereoselective Cross-Coupling of Vinylethylene Carbonates with Ketimine Esters to Generate (Z)-Tri- and Tetra-substituted Allylic Amino Acid Derivatives

Herein we report the palladium-catalyzed regio- and stereoselective cross-coupling of vinylethylene carbonates with ketimine esters to construct allylic amino acid scaffolds. This operationally simple protocol furnished (Z)-tri- and tetra-substituted allylic amino acid derivatives in good to excellent yields with distinguished geometric control under mild reaction conditions and proved to be sufficient in large-scale synthesis while retaining excellent reactivity and stereoselectivity, highlighting the practical value of this transformation.

Facile access to versatile aza-macrolides through iridium-catalysed cascade allyl-amination/macrolactonization

Direct access to benzo-fused aza-macrolides was successfully realised via the first iridium-catalysed intermolecular decarboxylative couplings of vinylethylene carbonates with isatoic anhydrides under relatively mild conditions.