Unsymmetrical Biaryls Research Articles

Palladium nanoparticle catalysis: borylation of aryl and benzyl halides and one-pot biaryl synthesis via sequential borylation-Suzuki–Miyaura coupling

Palladium nanoparticles generated in PEG catalyze the reaction of bis(pinacolato)diboron with various aryl/benzyl halides to afford aryl/benzyl boronates in high yield. Arylboronates thus prepared, have been directly used in the Suzuki–Miyaura coupling reaction with different aryl halides and benzyl halides in a convenient one-pot, two-step solvent free green synthesis of unsymmetrical biaryls and diarylmethanes.

ChemInform Abstract: Palladium‐Catalyzed Direct C—H Arylation of Unactivated Arenes with Aryl Halides.

AbstractAn unprecedented oxidative coupling of aryl iodides and bromides with unactivated arenes to yield either symmetrical or unsymmetrical biaryls is possible under conditions A) at different temperatures.

Selective Stille Coupling Reactions of 3-Chloro-5-halo(pseudohalo)-4H-1,2,6-thiadiazin-4-ones

A series of 3-chloro-5-halo(pseudohalo)-4H-1,2,6-thiadiazin-4-ones (halo/pseudohalo = Br, I, OTf) are prepared from 3,5-dichloro-4H-1,2,6-thiadiazin-4-one (3) in good yields. Of these the triflate reacts with tributyltin arenes (Stille couplings) chemoselectively to give only the 5-aryl-3-chloro-4H-1,2,6-thiadiazin-4-ones in high yields. This allowed the preparation of a series of unsymmetrical biaryl thiadiazines and ultimately a series of oligomers. Furthermore, treatment of 3-chloro-5-iodo-4H-1,2,6-thiadiazin-4-one (10) with Bu(3)SnH and Pd(OAc)(2) gave the bithiadiazinone which can also be further arylated via the Stille reaction to give bisthien-2-yl and bis(N-methylpyrrol-2-yl) analogs.

Ultrasound-assisted synthesis of unsymmetrical biaryls by Stille cross-coupling reactions

We describe herein an efficient method for the synthesis of unsymmetrically-substituted biphenyls using a sonochemical variation of the Stille coupling, whose results have also been compared with the conventional silent reaction. Ultrasound significantly enhances this useful organometallic transformation affording products in higher yields and in shorter reaction times than non-irradiated reactions. The scope has been explored with a selection of arylstannanes as precursors and, remarkably, no by-products resulting from homo-coupling could be detected.

Synthesis of Biaryls by Pd‐Catalyzed Decarboxylative Homo‐ and Heterocoupling of Substituted Benzoic Acids

AbstractBy carefully choosing the right substrate ratio, catalyst combination, and base, symmetrical and unsymmetrical biaryls can be readily synthesized through the Pd‐catalyzed decarboxylative homo‐ and heterocoupling of substituted benzoic acids. The reaction gave the desired products in 40–90 % yield and is compatible with 2‐nitro‐, 2‐methoxy‐, 2‐fluoro‐, and 2‐chloro‐substituted benzoic acids.

Copper catalyzed Gomberg–Buchmann–Hey reaction using aryldiazonium tosylate

Copper catalyzed modification of Gomberg–Bachmann–Hey reaction to synthesize symmetrical/unsymmetrical biaryls via diazotization of anilines with p-TSA and NaNO 2 system at 50 °C, in aromatic liquids as solvents and second partners was successfully developed. Aniline and 3-nitronaniline gave biphenyl and 3-nitrobiphenyl, respectively, with moderate yields. All para-substituted anilines gave comparatively higher yields while in the other cases including ortho-substituted anilines yields were lower. Except anilines with o-NHCOCH 3 and o-CONH 2 which gave symmetrical biaryls, all others gave selectively unsymmetrical biaryls.

Palladium-catalyzed direct C–H arylation of unactivated arenes with aryl Halides

An efficient palladium-catalyzed direct C–H arylation of unactivated arenes has been discovered. This method employs aryl halides as the direct coupling partners with arenes without using any external ligands. This catalysis opens a new methodology for the preparation of symmetrical as well as unsymmetrical biaryls in a user-friendly approach.

ChemInform Abstract: A Phosphine‐Free Carbonylative Cross‐Coupling Reaction of Aryl Iodides with Arylboronic Acids Catalyzed by Immobilization of Palladium in MCM‐41.

AbstractThe reaction affords unsymmetrical biaryl ketones (IV) and various electron‐donating and electron‐withdrawing grous on the aryl iodide (II) are tolerated.

Palladium‐Catalyzed Borylation of Aryl Mesylates and Tosylates and Their Applications in One‐Pot Sequential Suzuki–Miyaura Biaryl Synthesis

Top of the one-pots! The first palladium-catalyzed borylation of aryl tosylates and mesylates is described. The reaction conditions are mild and provide excellent functional-group compatibility (e.g., R=CN, CHO, COOMe, C(O)R, NH2, or NH-indole; see scheme). Pd/MeO-CM-phos allows one-pot sequential reactions in the preparation of unsymmetrical biaryls.

Cross-Coupling Reactions Catalyzed by Iron Group Metals and <i>N</i>-Heterocyclic Carbenes via Nonconventional Reaction Mechanisms

New cross-coupling reactions catalyzed by iron or iron group metals (IGMs), consisting of Fe, Co, and Ni with N-heterocyclic carbenes (NHCs), are described in this report. Highly selective biaryl cross-coupling reactions between aryl halides and aryl Grignard reagents were achieved by using a combination of fluoride salts of IGMs and NHCs. In the course of the study, an unexpected alkenylative cross-coupling between alkyl aryl sulfides and aryl Grignard reagents was found, in which a typical Ni/NHC catalyst displayed unprecedented reactivity toward sulfide substrates. Theoretical studies suggest that the biaryl coupling and the alkenylative coupling reactions proceed via two nonconventional mechanisms, which are substantially different from the widely-accepted cross-coupling mechanism: In the biaryl cross-coupling, treatment of the catalyst mixtures of IGM fluorides and NHCs with an excess amount of the aryl Grignard reagent results in the generation of organometalate complexes, [Ar1MIIF2]MgBr (M=Fe, Co, and Ni). These organometalate species undergo oxidative addition of aryl halide substrates to form intermediates in a high oxidation state (most likely a+IV state) possessing two different aryl groups, Ar1Ar2MIVF2. The heteroleptic diaryl organometallic intermediates collapse easily to afford unsymmetrical biaryls in a highly selective manner. On the other hand, the alkenylative coupling reaction using a Ni/NHC catalyst involves formation of a low-oxidation-state Ni(0)-thioaldehyde complex, which is transformed to an alkenylnickel species via α-deprotonation of the thioaldehyde and subsequent C-S bond cleavage of the resulting enethiolate intermediate. The alkenylnickel species undergoes transmetalation with an aryl Grignard reagent to form alkenyl/aryl coupling products via reductive elimination. The present cross-coupling reactions catalyzed by IGMs with NHC ligands provide highly selective Csp2-Csp2 coupling methods for the synthesis of unsymmetrical biaryls and styrene derivatives, offering an opportunity to gain new mechanistic insights into IGM-catalyzed cross-coupling reactions.

A phosphine-free carbonylative cross-coupling reaction of aryl iodides with arylboronic acids catalyzed by immobilization of palladium in MCM-41

The phosphine-free heterogeneous carbonylative cross-coupling of aryl iodides with arylboronic acids under an atmospheric pressure of carbon monoxide was achieved in anisole at 80 °C in the presence of a 3-(2-aminoethylamino)propyl-functionalized MCM-41-immobilized palladium(II) complex [MCM-41–2N–Pd(II)], yielding a variety of unsymmetrical biaryl ketones in good to high yield. This heterogeneous palladium catalyst exhibited higher activity and selectivity than PdCl2(PPh3)2, can be recovered and recycled by a simple filtration of the reaction solution, and used for at least 10 consecutive trials without any decrease in activity. Our system not only avoids the use of phosphine ligands, but also solves the basic problem of palladium catalyst recovery and reuse.

C–H arylation of unactivated arenes with aryl halides catalyzed by cobalt porphyrin

A general procedure for cobalt-catalyzed direct C–H arylation of unactivated arenes has been discovered. This method employs aryl halides as the direct coupling partners with arenes without using any Grignard-type reagents. This catalysis opens a new methodology for the preparation of symmetrical as well as unsymmetrical biaryls in a user-friendly approach.

Pd/C: An Efficient, Heterogeneous and Reusable Catalyst for Phosphane‐Free Carbonylative Suzuki Coupling Reactions of Aryl and Heteroaryl Iodides

AbstractThe carbonylative Suzuki coupling reaction of aryl boronic acid with different aryl and heteroaryl iodides was carried out to synthesize various unsymmetrical biaryl ketones by using Pd/C as an efficient, heterogeneous and reusable catalyst. The catalyst exhibits remarkable activity, and its reusability was tested up to four consecutive cycles. The reaction is applicable for various aryl and heteroaryl iodides having different steric and electronic properties. It provides good to excellent yield of the desired products. The developed protocol is advantageous with regard to the ease in handling the catalyst and the simple work‐up procedure; it is also an environmentally benign process with effective catalyst recyclability.

ChemInform Abstract: Controlled “Decomposition” of “Kinetic” Higher Order Cyanocuprates: A New Route to Unsymmetrical Biaryls

ChemInform Abstract: Controlled “Decomposition” of “Kinetic” Higher Order Cyanocuprates: A New Route to Unsymmetrical Biaryls

ChemInform Abstract: Synthesis of Unsymmetrical Biaryl Ketones (IV) via Palladium-Catalyzed Carbonylative Cross-Coupling Reaction of Arylboronic Acids (I) with Iodoarenes (II).

ChemInform Abstract: Synthesis of Unsymmetrical Biaryl Ketones (IV) via Palladium-Catalyzed Carbonylative Cross-Coupling Reaction of Arylboronic Acids (I) with Iodoarenes (II).

Metal-Free Regioselective Oxidative Biaryl Coupling Leading to Head-to-Tail Bithiophenes: Reactivity Switching, a Concept Based on the Iodonium(III) Intermediate

A new synthetic concept for obtaining unsymmetrical biaryl coupling products by an oxidative method is reported. Our synthetic strategy casts light on the reaction intermediate for switching the reactivity of 3-substituted thiophenes. On the basis of this strategy, a novel direct method for the synthesis of head-to-tail bithiophenes using hypervalent iodine(III) reagents has been developed.

Base-Free Aryl Coupling of Diazonium Compounds and Boronic Esters

The authors report an unprecedented application of self-activated boronic esters in a base-free cross-coupling reaction with diazonium salts under mild and user-friendly conditions. The protocol tolerates a wide range of functional groups and affords unsymmetrical biaryls in high yields.

ChemInform Abstract: Synthesis of Functionally Substituted Unsymmetrical Biaryls via a Novel Double Metal Catalyzed Coupling Reaction.

Abstract Unsymmetrical biaryls containing “reactive” functional groups (e.g., nitrile or ester groups) can be synthesized in an efficient manner by the direct Ni- or Pd-catalyzed coupling of aryl halides (X = Cl, Br, I) with aryl Grignard (or -lithium) reagents, provided that a catalytic amount of a Zn or Cd salt is also present.

Diaryl Sulfates as Electrophiles in Kumada Cross-Coupling Reactions

Diaryl sulfates were successfully used as electrophiles in nickel-catalyzed Kumada cross-couplings. The reaction affords unsymmetrical biaryls in high yields. The only byproducts are harmless inorganic salts.

Carbonylative cross-coupling of aryl halides with sodium tetraphenylborate catalyzed by MCM-41-supported bidentate phosphine palladium(II) complex

The first heterogeneous carbonylative cross-coupling reaction of aryl halides with sodium tetraphenylborate under an atmospheric pressure of carbon monoxide was achieved in DMF at 80 °C or 130 °C in the presence of a catalytic amount of MCM-41-supported bidentate phosphine palladium(II) complex [MCM-41-2P-Pd(II)] to yield unsymmetrical biaryl ketones in good to high yields. This polymeric palladium catalyst can be reused many times without any decrease in activity.