32865-61-5Relevant academic research and scientific papers
Steric effect of NHC ligands in Pd(II)–NHC-catalyzed non-directed C–H acetoxylation of simple arenes
Mandal, Tanmoy,Yadav, Sudha,Choudhury, Joyanta
, (2021/09/06)
Although there has been a lot of progress in oxidative arene C–H functionalization reactions catalyzed by Pd(II/IV) system, the non-directed, site-selective functionalization of arene molecules is still challenging. It has been established that ligands play a pivotal role in controlling rate- as well as selectivity-determining step in a catalytic cycle involving well-defined metal-ligand bonding. N-heterocyclic carbene (NHC) ligands have had a tremendous contribution in the recent extraordinary success of achieving high reactivity and excellent selectivity in many catalytic processes including cross-coupling and olefin-metathesis reactions. However, the immense potential of these NHC ligands in improving site-selectivity of non-directed catalytic C–H functionalization reactions of simple arenes is yet to be realized, where overriding the electronic bias on deciding selectivity is a burdensome task. The presented work demonstrated an initiative step in this regard. Herein, a series of well-defined discrete [Pd(NHCR′R)(py)I2] complexes with systematically varied degree of spatial congestion at the Pd centre, exerted through the R and R’ substituents on the NHC ligand, were explored in controlling the activity as well as the site-selectivity of non-directed acetoxylation of representative monosubstituted and disubstituted simple arenes (such as toluene, iodobenzene and bromobenzene, naphthalene and 1,2-dichlorobenzene). The resulting best yields were found to be 75% for toluene and 65% for bromobenzene with [Pd(NHCMePh)(py)I2], 75% for iodobenzene and 79% for naphthalene with [Pd(NHCMeMe)(py)I2], and 41% for 1,2-dichlorobenzene with [Pd(NHCCyCy)(py)I2]. Most importantly, with increasing the bulkiness of the NHC ligand in the complexes, the selectivity of the distal C-acetoxylated products in comparison to the proximal ones, was enhanced to a great extent in all cases. Considering the vast library of NHC ligands, this study underscores the future opportunity to develop more strategies to improve the activity and the crucial site-selectivity of C–H functionalization reactions in simple as well as complex organic molecules.
Regioselectivity Influences in Platinum-Catalyzed Intramolecular Alkyne O-H and N-H Additions
Costello, Jeff P.,Ferreira, Eric M.
supporting information, p. 9934 - 9939 (2019/12/24)
The steric and electronic drivers of regioselectivity in platinum-catalyzed intramolecular hydroalkoxylation are elucidated. A branch point is found that divides the process between 5-exo and 6-endo selective processes, and enol ethers can be accessed in good yields for both oxygen heterocycles. The main influence arises from an electronic effect, where the alkyne substituent induces a polarization of the alkyne that leads to preferential heteroatom attack at the more electron-deficient carbon. The electronic effects are studied in other contexts, including hydroacyloxylation and hydroamination, and similar trends in directionality are predominant although not uniformly observed.
Metathesis-active ligands enable a catalytic functional group metathesis between aroyl chlorides and aryl iodides
Lee, Yong Ho,Morandi, Bill
, p. 1016 - 1022 (2018/09/06)
Current methods for functional group interconversion have, for the most part, relied on relatively strong driving forces which often require highly reactive reagents to generate irreversibly a desired product in high yield and selectivity. These approaches generally prevent the use of the same catalytic strategy to perform the reverse reaction. Here we describe a catalytic functional group metathesis approach to interconvert, under CO-free conditions, two synthetically important classes of electrophiles that are often employed in the preparation of pharmaceuticals and agrochemicals—aroyl chlorides (ArCOCl) and aryl iodides (ArI). Our reaction design relies on the implementation of a key reversible ligand C–P bond cleavage event, which enables a non-innocent, metathesis-active phosphine ligand to mediate a rapid aryl group transfer between the two different electrophiles. Beyond enabling a practical and safer approach to the interconversion of ArCOCl and ArI, this type of ligand non-innocence provides a blueprint for the development of a broad range of functional group metathesis reactions employing synthetically relevant aryl electrophiles.
Highly Selective and Modular Synthesis of 3-Aryl-4-(arylethynyl)-2H-chromen-2-ones from 2-Iodoaryl 2-Arylacetates through a Carbonylative Sonogashira Coupling–Intramolecular Aldol Cascade Reaction
Chandrasekhar, Attoor,Ramkumar, Venkatachalam,Sankararaman, Sethuraman
, p. 4041 - 4049 (2016/08/24)
A modular method for the synthesis of 3-aryl-4-(arylethynyl)-2H-chromen-2-ones from 2-iodoaryl 2-arylacetates and arylacetylenes has been developed. The carbonylative Sonogashira coupling–intramolecular aldol casade reaction was carried out in the presence of Pd(PPh3)2(Cl)2as the catalyst. The one-pot approach that involves the in situ formation of the 2-iodoaryl 2-arylacetates from the corresponding 2-iodophenols and 2-arylacetyl chlorides followed by the palladium-catalyzed carbonylative annulation in the presence of the arylacetylene has also been described for the formation of the 3-aryl-4-(arylethynyl)-2H-chromen-2-ones.
Alkoxyboration: Ring-closing addition of B-O σ bonds across alkynes
Hirner, Joshua J.,Faizi, Darius J.,Blum, Suzanne A.
supporting information, p. 4740 - 4745 (2014/04/17)
For nearly 70 years, the addition of boron-X σ bonds to carbon-carbon multiple bonds has been employed in the preparation of organoboron reagents. However, the significantly higher strength of boron-oxygen bonds has thus far precluded their activation for addition, preventing a direct route to access a potentially valuable class of oxygen-containing organoboron reagents for divergent synthesis. We herein report the realization of an alkoxyboration reaction, the addition of boron-oxygen σ bonds to alkynes. Functionalized O-heterocyclic boronic acid derivatives are produced using this transformation, which is mild and exhibits broad functional group compatibility. Our results demonstrate activation of this boron-O σ bond using a gold catalysis strategy that is fundamentally different from that used previously for other boron addition reactions.
Expanded-ring N-heterocyclic carbenes efficiently stabilize gold(I) cations, leading to high activity in π-acid-catalyzed cyclizations
Morozov, Oleg S.,Lunchev, Andrey V.,Bush, Alexander A.,Tukov, Aleksandr A.,Asachenko, Andrey F.,Khrustalev, Victor N.,Zalesskiy, Sergey S.,Ananikov, Valentine P.,Nechaev, Mikhail S.
supporting information, p. 6162 - 6170 (2014/05/20)
A series of six- and seven-membered expanded-ring N-heterocyclic carbene (er-NHC) gold(I) complexes has been synthesized using different synthetic approaches. Complexes with weakly coordinating anions [(er-NHC)AuX] (X -=BF4-, NTf2-, OTf -) were generated in solution. According to their 13C NMR spectra, the ionic character of the complexes increases in the order X -=Cl-2--4-. Additional factors for stabilization of the cationic complexes are expansion of the NHC ring and the attachment of bulky substituents at the nitrogen atoms. These er-NHCs are bulkier ligands and stronger electron donors than conventional NHCs as well as phosphines and sulfides and provide more stabilization of [(L)Au+] cations. A comparative study has been carried out of the catalytic activities of five-, six-, and seven-membered carbene complexes [(NHC)AuX], [(Ph3P)AuX], [(Me2S)AuX], and inorganic compounds of gold in model reactions of indole and benzofuran synthesis. It was found that increased ionic character of the complexes was correlated with increased catalytic activity in the cyclization reactions. As a result, we developed an unprecedentedly active monoligand cationic [(THD-Dipp)Au]BF4 (1,3-bis(2,6-diisopropylphenyl) -3,4,5,6-tetrahydrodiazepin-2-ylidene gold(I) tetrafluoroborate) catalyst bearing seven-membered-ring carbene and bulky Dipp substituents. Quantitative yields of cyclized products were attained in several minutes at room temperature at 1 mol% catalyst loadings. The experimental observations were rationalized and fully supported by DFT calculations. What a difference a ring makes: Expanded-ring N-heterocyclic carbenes (er-NHC) surpass their five-membered ring counterparts, as well as Ph3P and Me2S, in the stabilization of cationic gold(I) species due to increased steric protection and electron-donating properties. A monoligand cationic [(THD-Dipp)Au]BF 4 (Dipp=2,6-diisopropylphenyl) complex bearing a seven-membered ring carbene and bulky Dipp substituents exhibits unprecedentedly high catalytic activity in indole and benzofuran synthesis (see scheme).
Benzofurans or isochromenes via the ring-opening cyclization of cyclopropene derivatives with organolithiums
Liu, Yu,Ma, Shengming
supporting information; experimental part, p. 720 - 723 (2012/04/17)
A new and efficient approach to benzocycles from cyclopropene derivatives is described. Deprotection by organolithiums and subsequent ring-opening cyclization of the related 2-cyclopropenyl phenyl or benzyl acetates generated benzofurans and isochromenes in one pot.
Design and pharmacophore modeling of biaryl methyl eugenol analogs as breast cancer invasion inhibitors
Abdel Bar, Fatma M.,Khanfar, Mohammad A.,Elnagar, Ahmed Y.,Badria, Farid A.,Zaghloul, Ahmed M.,Ahmad, Kadria F.,Sylvester, Paul W.,El Sayed, Khalid A.
experimental part, p. 496 - 507 (2010/05/02)
Cell invasion and migration are required for the parent solid tumor cells to metastasize to distant organs. Microtubules form a polarized network, enabling organelle and protein movement throughout the cell. Cytoskeletal elements coordinately regulate cell's motility, adhesion, migration, exocytosis, endocytosis, and division. Thus, microtubule disruption can be a useful target to control cancer cell invasion and metastasis. The phenolic ether methyl eugenol (1), the major component of the essential oil of the leaves of Melaleuca ericifolia Sm. (Myrtaceae), was used as a starting scaffold to design eleven new and three known anti-tubulin agents 2-15 using carbon-carbon coupling reactions. A computer-assisted approach was used to design these new biaryl derivatives using colchicine-binding site of tubulin as the molecular target and colchicine as an active ligand. Several derivatives showed potent inhibitory activity against MDA-MB-231 cell migration at the 1-4 μM dose range. The Z isomers, 4 and 15 were more active as invasion inhibitors compared to their structurally related E isomers, 2 and 14. The cytotoxic activities of compounds 2-15 against two breast cancer cell lines MDA-MB-231 and MCF-7 were evaluated. Anti-invasive activity of the semisynthetic derivatives is not due to a direct cytotoxic effect on MDA-MB-231. Analogs 2-15 may promote their anti-invasive activity through the induction of changes in cell morphology. A pharmacophore model was generated involving seven essential features for activity, which was consistent with a previously generated colchicine site inhibitors model.
Synthesis of novel oxygen heterocycles: 1,10-dioxa-cyclopenta[a]fluorene and benzo[b]naphtho[2, 1-d]furans via D?tz intramolecular benzannulation
Sen, Subhabrata,Kulkarni, Parag,Borate, Kailaskumar,Pai, Nandini R.
scheme or table, p. 4128 - 4131 (2009/12/01)
Novel fused heterocycles 1,10-dioxa-cyclopenta[a]fluorene and benzo[b]naphtho[2, 1-d]furans were synthesized via D?tz intramolecular benzannulation of alkyne tethered aryloxy chromium Fischer carbenes.
Novel PdII-mediated cascade carboxylative annulation to construct benzo[b]furan-3-carboxylic acids
Liao, Yun,Smith, Jennifer,Fathi, Reza,Yang, Zhen
, p. 2707 - 2709 (2007/10/03)
(Chemical Equation Presented) Benzo[b]furan-3-carboxylic acid (2) was generated from 1 by forming three new bonds in one step via a Pd II-mediated cascade carboxylative annulation. The proposed mechanism was supported by the observation of an u
