Iridium‐Catalyzed Enantioselective Allylic Alkylation with Functionalized Organozinc Bromides

Iridium‐catalyzed enantioselective allylic alkylation of branched racemic carbonates with functionalized alkylzinc bromide reagents is described. Enabled by a chiral Ir/(P,olefin) complex, the method described allows allylic substitution with various primary and secondary alkyl nucleophiles with excellent regio‐ and enantioselectivities. The developed reaction was showcased in a concise, asymmetric synthesis of (?)‐preclamol.     

Multicomponent Synthesis of Chiral Bidentate Unsymmetrical Unsaturated N‐Heterocyclic Carbenes: Copper‐Catalyzed Asymmetric CC Bond Formation

A multicomponent strategy was applied to the synthesis of chiral bidentate unsaturated hydroxyalkyl‐ and carboxyalkyl‐N‐heterocyclic carbene (NHC) precursors. The newly developed low‐cost chiral ligands derived from amino alcohols and amino acids were evaluated in copper‐catalyzed asymmetric conjugated addition and asymmetric allylic alkylation, which afforded the desired tertiary and quaternary carbon stereocenters with excellent regio‐ and enantioselectivities (up to 99:1 e.r.).     

Photoelectrochemical C−H Alkylation of Heteroarenes with Organotrifluoroborates

A photoelectrochemical method for the C?H alkylation of heteroarenes with organotrifluoroborates has been developed. The merger of electrocatalysis and photoredox catalysis provides a chemical oxidant‐free approach for the generation and functionalization of alkyl radicals from organotrifluoroborates. A variety of heteroarenes were functionalized using primary, secondary, and tertiary alkyltrifluoroborates with excellent regio‐ and chemoselectivity.     

Diverse meta‐C−H Functionalization of Arenes across Different Linker Lengths

Arenes containing conformationally flexible long alkyl chains have been successfully functionalized at the meta‐position. Good to excellent meta selectivity is achieved for systems with up to 20 atoms between the target C?H bond and the coordinating heteroatom of the directing group. The palladium‐catalyzed functionalization reactions include alkylation, cyanation, olefination, and acetoxylation. The meta selectivity is exclusively governed by the design of flexible pyrimidine‐based scaffolds.     

Asymmetric Synthesis of Spirocyclic β‐Lactams through Copper‐Catalyzed Kinugasa/Michael Domino Reactions

The first copper‐catalyzed highly chemo‐, regio‐, diastereo‐, and enantioselective Kinugasa/Michael domino reaction for the desymmetrization of prochiral cyclohexadienones is described. In the presence of a chiral copper catalyst, alkyne‐tethered cyclohexadienones couple with nitrones to generate the chiral spirocyclic lactams with excellent stereoselectivity (up to 97 % ee, >20:1 dr). The new method provides direct access to versatile highly functionalized spirocyclic β‐lactams possessing four contiguous stereocenters, including one quaternary and one tetra‐substituted stereocenter.     

An Original L‐shape,Tunable N‐Heterocyclic Carbene Platform for Efficient Gold(I) Catalysis

The synthesis and characterization of original NHC ligands based on an imidazo[1,5‐a]pyridin‐3‐ylidene (IPy) scaffold functionalized with a flanking barbituric heterocycle is described as well as their use as tunable ligands for efficient gold‐catalyzed C?N, C?O, and C?C bond formations. High activity, regio‐, chemo‐, and stereoselectivities are obtained for hydroelementation and domino processes, underlining the excellent performance (TONs and TOFs) of these IPy‐based ligands in gold catalysis. The gold‐catalyzed domino reactions of 1,6‐enynes give rise to functionalized heterocycles in excellent isolated yields under mild conditions. The efficiency of the NHC gold 5^Me complex is remarkable and mostly arises from a combination of steric protection and stabilization of the cationic Au^I active species by ligand 1^Me .     

An Original L‐shape,Tunable N‐Heterocyclic Carbene Platform for Efficient Gold(I) Catalysis

The synthesis and characterization of original NHC ligands based on an imidazo[1,5‐a]pyridin‐3‐ylidene (IPy) scaffold functionalized with a flanking barbituric heterocycle is described as well as their use as tunable ligands for efficient gold‐catalyzed C?N, C?O, and C?C bond formations. High activity, regio‐, chemo‐, and stereoselectivities are obtained for hydroelementation and domino processes, underlining the excellent performance (TONs and TOFs) of these IPy‐based ligands in gold catalysis. The gold‐catalyzed domino reactions of 1,6‐enynes give rise to functionalized heterocycles in excellent isolated yields under mild conditions. The efficiency of the NHC gold 5^Me complex is remarkable and mostly arises from a combination of steric protection and stabilization of the cationic Au^I active species by ligand 1^Me .     

Preparation of planar‐chiral multidonor phosphanylferrocene carboxamides and their application as ligands for palladium‐catalysed asymmetric allylic alkylation

Amide coupling of (S_p)‐2‐(diphenylphosphanyl)ferrocene‐1‐carboxylic acid with appropriate terminal amines mediated by 1‐hydroxybenzotriazole and a carbodiimide affords multi‐donor amides terminally functionalized with planar‐chiral (S_p)‐2‐(diphenylphosphanyl)ferrocen‐1‐yl moieties in good to excellent yields. Palladium catalysts based on these ligands efficiently promote asymmetric allylic alkylation of 1,3‐diphenylallyl acetate with in situ generated dimethyl malonate anion to give the C‐alkylated product with ees up to 93% at room temperature. Copyright © 2010 John Wiley & Sons, Ltd.     

A Gold‐Catalyzed Domino Cyclization Enabling Rapid Construction of Diverse Polyheterocyclic Frameworks

We report herein an efficient gold(I)‐catalyzed post‐Ugi domino dearomatization/ipso‐cyclization/Michael sequence that enables access to libraries of diverse (hetero)arene‐annulated tricyclic heterocycles. This process affords novel complex polycyclic scaffolds in moderate to good yields from readily available acyclic precursors with excellent chemo‐, regio‐, and diastereoselectivity. The power of this strategy has been demonstrated by the rapid synthesis of 40 highly functionalized polyheterocycles bearing indole, pyrrole, (benzo)furan, (benzo)thiophene, pyrazole, and electron‐rich arene groups in two operational steps.     

Chiral N,N′‐Dioxide‐Organocatalyzed Regio‐, Diastereo‐ and Enantioselective Michael Addition–Alkylation Reaction

A highly regio‐, diastereo‐ and enantioselective Michael addition–alkylation reaction between α‐substituted cyano ketones and (Z)‐bromonitrostyrenes has been realized by using a chiral N,N′‐dioxide as organocatalyst. A variety of substrates performed well in this reaction, and the corresponding multifunctionalized chiral 2,3‐dihydrofurans were obtained in up to 95 % yield with 95:5 dr and 93 % ee.     

Highly Regioselective Alkylation of Hexabenzocoronenes: Fundamental Insights into the Covalent Chemistry of Graphene

Hexa‐peri ‐hexabenzocoronides (HBC) was successfully used as a model system for investigating the complex mechanism of the reductive functionalization of graphene. The well‐defined molecular HBC system enabled deeper insights into the mechanism of the alkylation of reductively activated nanographenes. The separation and complete characterization of alkylation products clearly demonstrate that nanographene functionalization proceeds with exceptionally high regio‐ and stereoselectivities on the HBC scaffold. Experimental and theoretical studies lead to the conclusion that the intact basal graphene plane is chemically inert and addend binding can only take place at either preexisting defects or close to the periphery.     

Phosphine‐Catalyzed β,γ‐Umpolung Domino Reaction of Allenic Esters: Facile Synthesis of Tetrahydrobenzofuranones Bearing a Chiral Tetrasubstituted Stereogenic Carbon Center

An enantio‐, diastereo‐, regio‐, and chemoselective phosphine‐catalyzed β,γ‐umpolung domino reaction of allenic esters with dienones has been developed for the first time. The designed sequence, involving oxy‐Michael and Rauhut–Currier reactions, produced highly functionalized tetrahydrobenzofuranones, bearing a chiral tetrasubstituted stereogenic center, in up to 96 % ee.     

Nucleophile Coordination Enabled Regioselectivity in Palladium‐Catalyzed Asymmetric Allylic C−H Alkylation

Branched selectivity in asymmetric allylic C?H alkylation is enabled by using 2‐acylimidazoles as nucleophiles in the presence of a chiral phosphoramidite‐palladium catalyst. A wide range of terminal alkenes, including 1,4‐dienes and allylarenes, are nicely tolerated and provide chiral 2‐acylimidazoles in moderate to high yields and with high levels of regio‐, and enantio‐, and E/Z‐selectivities. Mechanistic studies using density‐functional theory calculations suggest a nucleophile‐coordination‐enabled inner‐sphere attack mode for the enantioselective carbon–carbon bond‐forming event.     

Electrooxidation Enables Selective Dehydrogenative [4+2] Annulation between Indole Derivatives

Dearomative annulation of indoles has emerged as a powerful tool for the preparation of polycyclic indoline‐based alkaloids. Compared with well‐established methods towards five‐membered‐ring‐fused indolines, the six‐membered‐ring‐fused indolines are rarely accessed under thermal conditions. Herein, a dearomative [4+2] annulation between different indoles is developed through an electrochemical pathway. This transformation offers a remarkably regio‐ and stereoselective route to highly functionalized pyrimido[5,4‐b]indoles under oxidant‐ and metal‐free conditions. Notably, this electrochemical approach maintains excellent functional‐group tolerance and can be extended as a modification tactic for pharmaceutical research. Preliminary mechanism studies indicate that the electrooxidation annulation proceeds through radical–radical cross‐coupling between an indole radical cation and an N‐centered radical generated in situ.     

Enantioselective Rhodium‐Catalyzed Allylic Alkylation of β,γ‐Unsaturated α‐Amino Nitriles: Synthetic Homoenolate Equivalents

An enantioselective rhodium‐catalyzed allylic alkylation of β,γ‐unsaturated α‐amino nitriles is described. This protocol provides a novel approach for the construction of β‐stereogenic carbonyl derivatives via the catalytic asymmetric alkylation of a homoenolate equivalent. The particularly challenging nature of this transformation is highlighted by the fact that three modes of selectivity must be manipulated, namely regio‐ and enantioselectivity, in addition to geometrical control. The γ‐stereogenic cyanoenamine products can be readily hydrolyzed in situ to afford the β‐substituted carboxylic acids, which in turn provide expedient access to a number of related carbonyl derivatives. Additionally, control experiments indicate that the chiral rhodium‐allyl intermediate facilitates the selective formation of the E‐cyanoenamine products, which is critical since the Z‐isomer affords significantly lower enantiocontrol.     

Synthesis of Novel Polycyclic Indole‐Annulated Thiopyranocoumarin Derivatives via Domino Knoevenagel–Hetero‐Diels–Alder Reaction in Aqueous Media

An efficient synthesis of polycyclic indole derivatives is achieved via domino Knoevenagel–hetero‐Diels–Alder reaction of O‐acrylated salicylaldehyde derivatives with dihydroindole‐2‐thiones in H₂O as solvent. The products are formed in good‐to‐excellent yields with high regio‐ and stereoselectivity.     

Asymmetric P−C Bond Formation: Diastereoselective Synthesis of Adjacent P,C‐Stereogenic Allylic Phosphorus Compounds

A novel catalytic asymmetric P?C bond formation between phosphinates/phosphine oxide and allylic carbonates was developed. This methodology could not only afford a variety of functionalized adjacent P,C‐stereogenic phosphorus compounds in high yields with high regio‐ and diastereoselectivities but also provide an alternative strategy to access enantiomerically enriched (S_P)‐phosphinates through kinetic resolution.     

Palladium‐Catalyzed Asymmetric Construction of Vicinal Tertiary and All‐Carbon Quaternary Stereocenters by Allylation of β‐Ketocarbonyls with Morita–Baylis–Hillman Adducts

Palladium‐catalyzed regio‐, diastereo‐, and enantioselective allylic alkylation of β‐ketocarbonyls with Morita–Baylis–Hillman adducts has been developed using a spiroketal‐based diphosphine (SKP) as the ligand, thus affording a range of densely functionalized products bearing vicinal tertiary and all‐carbon quaternary stereodyad in high selectivities. The utility of the protocol was demonstrated by the facile synthesis of some complex molecules by simple product transformations.     

Enantioselective Template‐Directed [2+2] Photocycloadditions of Isoquinolones: Scope,Mechanism and Synthetic Applications

A strategy for the enantioselective [2+2] photocycloaddition of isoquinolones with alkenes is presented, in which the formation of a supramolecular complex between a chiral template and the substrate ensures high enantioface differentiation by shielding one face of the substrate. Fifteen different electron‐deficient alkenes and ten different substituted isoquinolones undergo efficient photocycloaddition, yielding the cyclobutane products in excellent yields and with outstanding regio‐, diastereo‐ and enantioselectivities (up to 99 % ee). The mechanism of the reaction is investigated by means of triplet sensitization/quenching and radical clock experiments, the results of which are consistent with the involvement of a triplet excited state and a 1,4‐biradical intermediate. The variety of functionalized cyclobutanes obtained using this approach can be further increased by straightforward synthetic transformations of the photoadducts, allowing rapid access to libraries of compounds for various applications.     

Rhodium‐Catalyzed Regioselective N2‐Alkylation of Benzotriazoles with Diazo Compounds/Enynones via a Nonclassical Pathway

A novel rhodium‐catalyzed highly selective N²‐alkylation of benzotriazoles with diazo compounds/enynones is achieved, providing N²‐alkylated benzotriazoles in good to excellent yields and with excellent N² selectivities. Importantly, different to traditional carbene insertion into X?H (X=N, O etc) bonds, DFT calculations disclose that this selective N²‐alkylation probably proceeds through a formal 1,3‐ rather than 1,2‐H shift to give the final products.