Rhodium-Catalyzed Addition of Aryl Boronic Acids to 2,2-Disubstituted Malononitriles

β-Ketonitriles bearing a quaternary carbon at the 2-position were prepared through Rh-catalyzed addition of aryl boronic acids to 2,2-disubstituted malononitriles. In contrast to the previously described transnitrilative cyanation of aryl boronic acids with dialkylmalononitriles, the present reaction avoids retro-Thorpe collapse of the intermediate addition product through the use of a milder base. The reaction was amenable to a variety of aryl boronic acids and disubstituted malononitriles, providing a diverse array of β-ketonitriles. The products could be further derivatized to valuable chiral α,α-disubstituted-β-aminonitriles through addition reactions to the corresponding N-tert-butanesulfinyl imines.     

Decarboxylative Conjunctive Cross‐coupling of Vinyl Boronic Esters using Metallaphotoredox Catalysis

The synthesis of complex alkyl boronic esters through conjunctive cross‐coupling of vinyl boronic esters with carboxylic acids and aryl iodides is described. The reaction proceeds under mild metallaphotoredox conditions and involves an unprecedented decarboxylative radical addition/cross‐coupling cascade of vinyl boronic esters. Excellent functional‐group tolerance is displayed, and application of a range of carboxylic acids, including secondary α‐amino acids, and aryl iodides provides efficient access to highly functionalized alkyl boronic esters. The decarboxylative conjunctive cross‐coupling was also applied to the synthesis of sedum alkaloids.     

Chelation‐Assisted Cross‐Coupling of Anilines through In Situ Activation as Diazonium Salts with Boronic Acids under Ligand‐, Base‐, and Salt‐Free Conditions

We describe the coupling of anilines with aryl boronic acids, under ligand‐, base‐, and salt‐free conditions at room temperature. This new reaction proceeds through the formation of an aryl palladium alkoxo complex, which allows the transmetalation step with aryl boronic acids without any external base. Importantly, this sustainable procedure generates only environmentally friendly byproducts such as tBuOH, H₂O, N₂, and B(OH)₃. The reaction mechanism has been deeply investigated through experimental and theoretical studies.     

Synthesis of 4‐halo‐2 (5H)‐furanones and their suzuki‐coupling reactions with organoboronic acids. A general route to 4‐aryl‐2 (5 H) ‐furanones

4‐Halo‐2(5H)‐furanones were prepared by the halolactonization of 2,3‐allenoic acids. The subsequent Suzuki coupling reaction of 4‐halo 2(5H)‐furanones with aryl boronic acids was carried out to produce 4‐aryl‐2(5H)‐furanones in excellent yields.     

Rhodium‐Catalyzed Arylation of Cyclopropenes Based on Asymmetric Direct Functionalization of Three‐Membered Carbocycles

A variety of highly diastereo‐ and enantiomerically enriched arylcyclopropanes is obtained through the asymmetric rhodium‐catalyzed arylation reaction of achiral nonfunctionalized cyclopropene derivatives with commercially available aryl boronic acids in the presence of (R,S)‐Josiphos.     

The Development of Copper‐Catalyzed Aerobic Oxidative Coupling of H‐Tetrazoles with Boronic Acids and an Insight into the Reaction Mechanism

The development of a highly efficient and practical protocol for the direct C?N coupling of H‐tetrazole and boronic acid was presented. A careful and patient optimization of a variety of reaction parameters revealed that this conventionally challenge reaction could indeed proceed efficiently in a very simple system, that is, just by stirring the tetrazoles and boronic acids under oxygen in the presence of different Cu^I or Cu^II salts with only 5 mol % loading in DMSO at 100 °C. Most significantly, the reaction could proceed very smoothly in a regiospecific manner to afford the 2,5‐disubstituted tetrazoles in high to excellent yields. A mechanistic study revealed that both tetrazole and DMSO are crucial for the generation of catalytically active copper species in the reaction process in addition to their role as reactant and solvent, respectively. It is demonstrated that in the reaction cycle, the Cu^I catalyst could be oxidized to Cu^II by oxygen to form a [CuT₂D] complex (T=tetrazole anion; D=DMSO) through an oxidative copper amination reaction. The Cu^II complex thus formed was confirmed to be the real catalytically active copper species. Namely, the Cu^II complex disproportionates to aryl Cu^III and Cu^I in the presence of boronic acid. Facile elimination of the Cu^III species delivers the C?N‐coupled product. The results presented herein not only provide a reliable and efficient protocol for the synthesis of 2,5‐disubstituted tetrazoles, but most importantly, the mechanistic results would have broad implications for the de novo design and development of new methods for Cu‐catalyzed coupling reactions.     

Palladium‐Catalyzed Enantioselective Cacchi Reaction: Asymmetric Synthesis of Axially Chiral 2,3‐Disubstituted Indoles

We report herein the first examples of a palladium‐catalyzed enantioselective Cacchi reaction for the synthesis of indoles bearing a chiral C2‐aryl axis. In the presence of a catalytic amount of Pd(OAc)₂ and (R,R)‐QuinoxP* ligand, reaction of N‐aryl(alkyl)sulfonyl‐2‐alkynylanilides with arylboronic acids under oxygen atmosphere afforded enantioenriched 2,3‐disubstituted indoles in high yields and enantioselectivity. The indole ring is constructed de novo in this process and a complexation‐induced chirality transfer is proposed to account for the observed enantioselectivity.     

Synthesis of 5‐Amino‐3,3‐dimethyl‐7‐phenyl‐3H‐[1,2]oxathiolo[4,3‐b]pyridine‐6‐carbonitrile 1,1‐Dioxides

The reaction of 4‐amino‐5,5‐dimethyl‐5H‐1,2‐oxathiole 2,2‐dioxide ( 1 ) with 2‐(arylidene)malononitriles 2 in ethanol, at reflux, using piperidine as catalyst, afforded 5‐amino‐3,3‐dimethyl‐7‐aryl‐3H‐[1,2]oxathiolo[4,3‐b]pyridine‐6‐carbonitrile 1,1‐dioxides ( 3 ) in moderate chemical yields.     

Rhodium(III)‐Catalyzed [4+1] Annulation of Aromatic and Vinylic Carboxylic Acids with Allenes: An Efficient Method Towards Vinyl‐Substituted Phthalides and 2‐Furanones

A highly regio‐ and stereoselective synthesis of 3,3‐disubstituted phthalides from aryl carboxylic acids and allenes using a rhodium(III) catalyst has been demonstrated. The reaction features broad functional group tolerance and provides a simple and straightforward route to the synthesis of various 3‐vinyl‐substituted phthalides. Furthermore, the catalytic reaction can also be applied to the synthesis of biologically active 5‐vinyl‐substituted 2‐furanones from α,β‐unsaturated carboxylic acids and allenes. The reactions proceed through a carboxylate‐assisted ortho‐C?H activation and [4+1] annulation. The preliminary mechanistic studies suggest that a C?H cleavage is the rate‐determining step.     

One‐pot Synthesis of 2,5‐Disubstituted‐1,3,4‐oxadiazoles Based on the Reaction of N,N‐Dimethyl Amides with Acid Hydrazides

Convenient and efficient one pot method for the synthesis of 2,5‐disubstituted‐1,3,4‐oxadiazoles based on the reaction of N,N‐dimethyl amides with acid hydrazides has been developed. The methodology is applied to a wide range of difference aryl hydrazide and difference N,N‐dimethyl amides to 2,5‐disubstituted‐1,3,4‐oxadiazoles yield the in good to excellent yields. It will be possible wide useful application in synthesis.     

The Discovery of a Palladium(II)‐Initiated Borono‐Catellani Reaction

Reported is a novel palladium(II)‐initiated Catellani‐type reaction that utilizes widely accessible aryl boronic acids as the substrates instead of aryl halides, thereby greatly expanding the existing scope of this powerful transformation. This borono‐Catellani reaction was promoted by cooperative catalysis between Pd(OAc)₂ and the inexpensive 5‐norbornene‐2‐carbonitrile. Practicality is the striking feature of the reaction: it is run open to air at ambient temperature and no phosphine ligand is needed. This mild, chemoselective, and scalable protocol is compatible with a large range of readily available functionalized aryl boronic acids and bromides, as well as terminating olefins (50 examples, 39–97 % yields). Moreover, the orthogonal reactivity between the borono‐Catellani and classical Catellani reaction was demonstrated. This work is expected to open new avenues for developing novel Catellani‐type reactions.     

Decarboxylative Conjunctive Cross-coupling of Vinyl Boronic Esters using Metallaphotoredox Catalysis

The synthesis of complex alkyl boronic esters through conjunctive cross-coupling of vinyl boronic esters with carboxylic acids and aryl iodides is described. The reaction proceeds under mild metallaphotoredox conditions and involves an unprecedented decarboxylative radical addition/cross-coupling cascade of vinyl boronic esters. Excellent functional-group tolerance is displayed, and application of a range of carboxylic acids, including secondary α-amino acids, and aryl iodides provides efficient access to highly functionalized alkyl boronic esters. The decarboxylative conjunctive cross-coupling was also applied to the synthesis of sedum alkaloids.     

Direct Monofluoromethylthiolation with S‐(Fluoromethyl) Benzenesulfonothioate

An electrophilic shelf‐stable monofluoromethylthiolating reagent S ‐(fluoromethyl) benezenesulfonothioate ( 1 ) was developed. In the presence of a copper catalyst, reagent 1 coupled with a variety of aryl boronic acids to give the corresponding monofluoromethylthiolated arenes in high yields. In addition, addition of reagent 1 to alkyl alkenes in the presence of a silver catalyst gave alkyl monofluoromethylthioethers in high yields.     

Stereoselective Csp3–Csp2 Bond‐Forming Reactions by Transition‐Metal‐Free Reductive Coupling of Cyclic Tosylhydrazones with Boronic Acids

The reactions between alkenylboronic acids and tosylhydrazones derived from substituted cyclohexanones lead to the construction of disubstituted cyclohexanes with total regio‐ and stereoselectivity. In these transition‐metal‐free processes, a Csp³?Csp² and Csp³?H bond are formed on the same carbon atom. The stereoselective reaction is general for 2‐, 3‐, and 4‐substituted cyclohexanone tosylhydrazones, as well as for 2‐substituted cyclopentanones. However, no stereoselectivity is observed for acyclic derivatives. DFT computational modeling suggests that the stereoselectivity of the reaction is determined by the approach of the boronic acid to the diazocyclohexane on its most stable chair conformation through an equatorial trajectory.     

Visible‐Light‐Mediated Chan–Lam Coupling Reactions of Aryl Boronic Acids and Aniline Derivatives

The copper(II)‐catalyzed aerobic oxidative coupling reaction between aryl boronic acids and aniline derivatives was found to be improved significantly under visible‐light‐mediated photoredox catalysis. The substrate scope of this oxidative Chan–Lam reaction was thus expanded to include electron‐deficient aryl boronic acids as viable starting materials.     

Facile and Versatile Synthesis of End‐Functionalized Poly(phenylacetylene)s: A Multicomponent Catalytic System for Well‐Controlled Living Polymerization of Phenylacetylenes

A rhodium‐based multicomponent catalytic system for well‐controlled living polymerization of phenylacetylenes has been developed. The catalytic system is composed of readily available and bench‐stable [Rh(nbd)Cl]₂, aryl boronic acid derivatives, diphenylacetylene, 50 % aqueous KOH, and PPh₃. This system offers a method for the facile and versatile synthesis of various end‐functionalized cis‐stereoregular poly(phenylacetylene)s because components from aryl boronic acids and diphenylacetylene were introduced to the initiating end of the polymers. The polymerization reaction shows a typical living nature with a high initiation efficiency, and the molecular weight of the resulting poly(phenylacetylene)s can be readily controlled with very narrow molecular‐weight distributions (M_w/M_n=1.02–1.09). The experimental results suggest that the present catalytic system has a higher polymerization activity than the polymerization activities of other rhodium‐based catalytic systems previously reported.     

Metal‐Free Tandem Rearrangement/Lactonization: Access to 3,3‐Disubstituted Benzofuran‐2‐(3H)‐ones

A novel metal‐free synthesis of 3,3‐disubstituted benzofuran‐2‐(3H)‐ones through reacting α‐aryl‐α‐diazoacetates with triarylboranes is presented. Initially, triarylboranes were successfully investigated in α‐arylations of α‐diazoacetates, however in the presence of a heteroatom in the ortho position, the boron enolate intermediate undergoes an intramolecular rearrangement to form a quaternary center. The intermediate cyclizes to afford valuable 3,3‐disubstituted benzofuranones in good yields.     

Base‐Free Conditions for Rhodium‐Catalyzed Asymmetric Arylation To Produce Stereochemically Labile α‐Aryl Ketones

The asymmetric arylation of 2,2‐dialkyl cyclopent‐4‐ene‐1,3‐diones with aryl boronic acids was found to be efficiently catalyzed by a chiral diene–rhodium μ‐chloro dimer, [{RhCl((R)‐diene*)}₂], in the absence of bases in toluene/H₂O to give 2,2‐dialkyl 4‐aryl cyclopentane‐1,3‐diones in high yields with high enantioselectivity. Such compounds can not be obtained with high enantiomeric purity under the standard basic conditions used for rhodium‐catalyzed asymmetric arylation because the α‐aryl ketone products undergo racemization under the basic conditions.     

PhSO2SCF2H: A Shelf‐Stable,Easily Scalable Reagent for Radical Difluoromethylthiolation

A new shelf‐stable and easily scalable difluoromethylthiolating reagent S‐(difluoromethyl) benzenesulfonothioate (PhSO₂SCF₂H) was developed. PhSO₂SCF₂H is a powerful reagent for radical difluoromethylthiolation of aryl and alkyl boronic acids, decarboxylative difluoromethylthiolation of aliphatic acids, and a phenylsulfonyl‐difluoromethylthio difunctionalization of alkenes under mild reaction conditions.     

A Highly Efficient Catalyst for the Suzuki Cross‐coupling Reaction of 3‐Chloro‐5‐oxadiazol‐2‐yl Pyridine

A facile access to diversely substituted 3‐aryl/heteroaryl‐5‐oxadiazol‐2‐yl‐pyridines using PdCl₂(dtbpf) as palladium precursor has been developed. The method is compatible with a wide range of aryl/heteroaryl boronic acids.