68294-33-7

Although cross-coupling reactions of amides by selective N?C cleavage are one of the most powerful and burgeoning areas in organic synthesis due to the ubiquity of amide bonds, the development of mechanochemical, solid-state methods remains a major challe

Microtubule targeting agents (MTAs) are among the most successful chemotherapeutic drugs, but their efficacy is often limited by the development of multidrug resistance (MDR). Therefore, the development of novel MTAs with the ability to overcome MDR is urgently needed. In this contribution, through modification of the unsymmetric biaryl compounds, we discovered a novel compound dxy-1-175 with potent anti-proliferative activity against cancer cells. Mechanistic study revealed that dxy-1-175 inhibited tubulin polymerization by interacting with the colchicine-binding site of tubulin, which caused cell cycle arrest at G2/M phase. Based on the predicted binding model of dxy-1-175 with tubulin, a series of new 4-benzoylbiphenyl analogues were designed and synthesized. Among them, the hydrochloride compound 12e with improved solubility and good stability in human liver microsome, exhibited the most potent anti-proliferative activity with IC50 value in the low nanomolar range, and markedly inhibited the growth of breast cancer 4T1 xenograft in vivo. Notably, 12e effectively overcame P-gp-mediated MDR and our preliminary data suggested that 12e may not be a substrate of P-glycoprotein (P-gp). Taken together, our study reveals a novel MTA 12e targeting the colchicine-binding site with potent anticancer activity and the ability to circumvent MDR.

The actually direct Suzuki-Miyaura coupling with "protected" R-B(dan) (dan = naphthalene-1,8-diaminato) was demonstrated to smoothly occur without in situ deprotection of the B(dan) moiety. The use of t-BuOK (Ba(OH)2 in some cases) as a base under anhydrous conditions is the key to the successful cross-coupling, where R-B(dan) is readily converted into a transmetalation-active borate-form, regardless of the well-accepted diminished boron-Lewis acidity.

The Suzuki-Miyaura arylation of aryl trifluoromethyl sulfones via C-SO2 bond cleavage has been developed by means of cooperative palladium/rhodium catalysis. A series of aryl trifluoromethyl sulfones and arylboronic acid neopentylglycol esters are converted to the corresponding biaryls. Mechanistic investigations suggest that (1) the rhodium catalyst mediates the transfer of the aryl ring from arylboronate to palladium, resulting in the acceleration of the transmetalation step, and (2) the C-C bond-forming reductive elimination step is the turnover-limiting step.

A practical nickel-catalyzed cross-coupling of (hetero)aryl or alkynylzinc pivalates with various unsaturated nonaflates or triflates is described. Organozinc pivalates allow these cross-couplings to take place with high yields and a low catalyst loading (0.5 mol %). Couplings with (E)- and (Z)-alkenyl triflates proceed with retention of configuration.

The Suzuki-Miyaura cross-coupling reaction is one of the most reliable methods for the construction of carbon-carbon bonds in solution. However, examples for the corresponding solid-state cross-coupling reactions remain scarce. Herein, we report the first broadly applicable mechanochemical protocol for a solid-state palladium-catalyzed organoboron cross-coupling reaction using an olefin additive. Compared to previous studies, the newly developed protocol shows a substantially broadened substrate scope. Our mechanistic data suggest that olefin additives might act as dispersants for the palladium-based catalyst to suppress higher aggregation of the nanoparticles, and also as stabilizer for the active monomeric Pd(0) species, thus facilitating these challenging solid-state C-C bond forming cross-coupling reactions.

Nickel-catalyzed Negishi-type cross-coupling of aryl methyl sulfoxides with arylzinc reagents has been developed. By consuming the catalyst-oxidizing methanesulfenate anion through oxidative homocoupling of the arylzinc reagent, smooth catalyst turnover c

N,N,O-Tridentate palladium(ii) complexes [Pd(OAc){R-C4H8N2(CH2Ar)}] (R = Ph, Ar = 4-tBu-C6H3-OH (4a)) and [2,4-di-tBu-C6H2-OH, R = benzyl (4b)] 4a and 4b have been synthesized from the corresponding 2-((4-arylpiperazin-1-yl)methyl)phenol ligands 3a and 3b in quantitative yields. The synthesized ligands and their palladium(ii) complexes were characterized by NMR, IR and HRMS analyses. Complex 4a has been used as an efficient catalyst for the Suzuki cross-coupling reaction of 5-iodovanillin and 5-bromosalicylaldehyde with various arylboronic acids in low catalytic amounts (0.01-0.05 mol% of 4a). Moreover, this catalytic system is even applicable for Suzuki coupling reactions of deactivated aryl bromides and aryl chlorides, affording the cross-coupling products in good to excellent yields with a broad substrate scope.

A novel, highly versatile and efficient method has been developed for the Barbier-Grignard-type arylation of ketones and an unexpected cross-coupling of phenolic ketones was observed using unactivated bromides and magnesium in tetrahydrofuran/toluene at 96°C promoted by multicatalysts of cupric bromide (15 mol%), bismuth chloride (5 mol%) and silver bromide (10 mol%). The substituent and electronic effects on the reaction have been discussed. High yields of arylation and cross-coupling have been attained under mild conditions. A novel reasonable mechanism involving a quinone intermediate is proposed. The high chemical selectivity in the cross-coupling to the hydroxy group of phenolic ketones should help ketones find new applications.

P,N,N-Pincer nickel complexes [Ni(Cl){N(2-R2PC6H 4)(2′-Me2NC6H4)}] (R = Ph, 3a; R = Pri, 3b; R = Cy, 3c) were synthesized and their catalysis toward the Kumada or Negishi cross-coupling reaction of aryl fluorides and chlorides was evaluated. Complex 3a effectively catalyzes the cross-coupling of (hetero)aryl fluorides with aryl Grignard reagents at room temperature. Complex 3a also catalyzes the cross-coupling of (hetero)aryl chlorides and arylzinc reagents at 80 °C with low catalyst loadings and good functional group compatibility. the Partner Organisations 2014.

Ni(PCy3)2Cl2 was demonstrated to effectively catalyze cross-coupling of aryl fluorides and organozinc reagents. Both electron-poor and -rich aryl fluorides can react effectively with nucleophiles including aryl-, methyl-, and benzylzinc chlorides. A wide range of substituents and functional groups are tolerated. In the presence of a directing group, PhC(O), the reaction is selective for cleavage of the C-F bond ortho to the carbonyl substituent in a difluoroarene.

Organozinc compounds of the type R1—Ar1—ZnY (1) can be reacted with different functionalized aryl halides R2—Ar2—X (2) in the presence of catalytic amounts of Ni or Fe in a polar solvent or solvent mixture to form polyfunctional biaryles of the type R1—Ar1—Ar2—R2 (3). Organozinc compounds of the type (1) can be represented by the transmetallation reaction of functionalized aryl magnesium halides or lithium aryl compounds with e.g. ZnBr2.

The photosolvolysis of several biphenyl methanols (Ph-PhCH[Ph]OH) substituted with hydroxy or methoxy groups on the benzene ring not containing the -CH(Ph)OH moiety has been studied in aqueous solution. This work is a continuation of our studies of photosolvolysis of hydroxy-substituted arylmethanols that generate quinone methide intermediates, some of which are known to be relevant intermediates in toxicology and in biological and organic chemistry in general. In this study, we further probe the ability of the biphenyl ring system to transmit charge from the ring substituted with a potential electron-donating group (hydroxy and methoxy) to the adjacent benzene ring that contains a labile benzyl alcohol moiety. We show that in systems with a hydroxy substituent, biphenyl quinone methides (BQM) are the first formed intermediates that are detectable by nanosecond laser flash photolysis, and are responsible for the observed overall photosolvolysis reaction of these compounds. The highly conjugated BQM are found to absorb at long wavelengths (λmax 580 and ～750 nm for the p,p′ and o,p′-isomers, respectively) with relatively long lifetimes in neutral aqueous solution (500 and 30 μs, respectively). The BQM from the o,p′-isomer was found to undergo a competing intramolecular Friedel-Crafts alkylation, to give a fluorene derivative.

A combination of diethyl phosphite-DMAP and Ni(II) salts forms a very effective catalytic system for the cross-coupling reactions of arylzinc halides with aryl, heteroaryl, and alkenyl bromides, chlorides, triflates, and nonaflates. The choice of solvent is quite important and the mixture of THF-N-ethylpyrrolidinone (NEP) (8:1) was found to be optimal. The reaction usually requires only 0.05 mol % of NiCl2 or Ni(acac)2 as catalyst and proceeds at room temperature within 1-48 h.

N,N′-Bis(2,6-diisopropylphenyl)imidazolium chloride associated with nickel(II) acetylacetonate (3-5 mol%) was used as catalyst to efficiently cross-couple functionalized aryl bromides with organomanganese reagents. The reactions were performed between 0°C and room temperature, giving unsymmetrical biaryls in 0.25 to 24 h with 52 to 100% yields for isolated materials. Aryl chlorides showed slightly diminished reactivity in Ni/2 IPr-catalyzed cross-couplings and good yields could only be attained with activated or neutral substrates.

A range of aromatic organocopper or organomagnesium compounds undergo smooth cross-coupling reactions with aryl bromides, chlorides, fluorides and tosylates, leading to polyfunctionalized aromatics or heterocycles in the presence of cobalt salts (5-7.5 mol%) as catalysts. Very mild reaction conditions are needed and, in the case of cross-coupling with organocopper compounds, Bu4NI (1 equiv) and 4-fluorostyrene (20 mol%) are essential as promoters for successful couplings. Georg Thieme Verlag Stuttgart.

(Chemical Equation Presented) The combination of diethyl phosphite and DMAP as ligands for nickel in an 8:1 THF-N-ethylpyrrolidinone (NEP) mixture allows a very efficient cross-coupling reaction to be performed between various functionalized arylzinc halides and aryl bromides, triflates and activated chlorides. The reaction proceeds at 25°C within 1-48 h and requires only 0.05 mol % of the nickel catalyst.

(Chemical Equation Presented) Polyfunctionalized biphenyl and heteroaromatic compounds were formed in the presence of [Co(acac)2], Bu4Nl, and 4-fluorostyrene (3) through a smooth cross-coupling reaction between organocopper reagents 1, prepared by the transmetalation of functionalized aryl magnesium halides with CuCN·2 LiCl, and aryl halides 2 that bear electron-withdrawing substituents. acac = acetylacetonate, DME = 1,2-dimethoxyethane, DMPU = 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone.

Evidence is presented for the photochemical generation of novel biphenyl quinone methide (BQM)-type intermediates on photolysis of hydroxybiphenyl alkenes 7 and 8 and hydroxybiphenyl alcohols 9 and 10. Mechanistic investigations utilizing product, fluorescence, and nanosecond laser flash photolysis (LFP) studies indicate two distinct pathways for the formation of these BQMs depending upon the functional groups of the progenitor. Formal excited-state intramolecular proton transfer (ESIPT) between the phenol and the alkene led to BQMs upon irradiation of the hydroxybiphenyl alkenes 7 and 8, while excited-state proton transfer (ESPT) to solvent followed by dehydroxylation was responsible for BQM formation from the hydroxybiphenyl alcohols 9 and 10. Photolysis of 7 and 8 in aqueous CH3CN gave photohydration products via attack of water on the respective BQMs, while photolysis of the analogous methyl ethers (of the phenolic moiety) gave only carbocation intermediates. Hydroxybiphenyl alcohols 9 and 10 yielded the corresponding photomethanolysis products in aqueous methanol, through attack of CH3OH on the respective BQMs. Although no evidence was found for BQM formation in LFP studies of 8 and 10, due to its suspected short lifetime, the respective diaryl carbocation (λmax 420 nm, τ = 8.5 μs) has been observed upon irradiation of 8 in 2,2,2-trifluoroethanol. A BQM (λmax 580 nm) was observed for 9 but not for 10, the latter having more complex chemistry on laser excitation, resulting in a transient that appears to mask any BQM absorption. Significant quenching of fluorescence from the hydroxybiphenyl alkenes at low water content implies that H 2O is directly involved in reaction from the singlet excited state. The decrease in fluorescence intensity of 8 was found to depend on [H 2O]3; however, the distance required for ESIPT in these systems is too large to be bridged by a water trimer. The nonlinear quenching has been attributed to deprotonation of the phenol by two water molecules, with concerted protonation at the alkene by another molecule of water. Fluorescence quenching of the hydroxybiphenyl alcohols required much higher water content, implying a different mechanism of reaction, consistent with the proposal of ESPT (to solvent water) followed by dehydroxylation.

[reaction--see text] N,N-Bis-(2,6-diisopropylphenyl)dihydroimidazolium chloride with palladium(II) acetate (2 mol %) was used as catalyst, without added base, to efficiently cross couple aryl, vinyl, and alkyl boronates and boronic acids with aryldiazonium tetrafluoroborate substrates. The reactions were performed at 0 degrees C or rt, giving product in 2 to 4 h with 80 to 90% yields for isolated materials. Diazonium ions, formed in situ, also cross couple under these conditions.