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Showing papers in "Journal of Organic Chemistry in 2003"


Journal ArticleDOI
TL;DR: A new method for calculating van der Waals volume has been developed, based on Bondi radii, and the results show that the van Der Waals volumes calculated from VABC are equivalent to the computer-calculated van derWaals volumes for organic compounds.
Abstract: The van der Waals volume is a widely used descriptor in modeling physicochemical properties. However, the calculation of the van der Waals volume (VvdW) is rather time-consuming, from Bondi group contributions, for a large data set. A new method for calculating van der Waals volume has been developed, based on Bondi radii. The method, termed Atomic and Bond Contributions of van der Waals volume (VABC), is very simple and fast. The only information needed for calculating VABC is atomic contributions and the number of atoms, bonds, and rings. Then, the van der Waals volume (A3/molecule) can be calculated from the following formula: VvdW = ∑ all atom contributions − 5.92NB − 14.7RA − 3.8RNR (NB is the number of bonds, RA is the number of aromatic rings, and RNA is the number of nonaromatic rings). The number of bonds present (NB) can be simply calculated by NB = N − 1 + RA + RNA (where N is the total number of atoms). A simple Excel spread sheet has been made to calculate van der Waals volumes for a wide r...

531 citations


Journal ArticleDOI
TL;DR: Rate constants, k(ArOH/dpph*)(S), for hydrogen atom abstraction from 13 hindered and nonhindered phenols by the diphenylpicrylhydrazyl radical, dpph*, have been determined in n-heptane and a number of alcoholic and nonalcoholic, hydrogen-bond accepting solvents.
Abstract: Rate constants, k(ArOH/dpph*)(S), for hydrogen atom abstraction from 13 hindered and nonhindered phenols by the diphenylpicrylhydrazyl radical, dpph*, have been determined in n-heptane and a number of alcoholic and nonalcoholic, hydrogen-bond accepting solvents. Abnormally enhanced k(ArOH/dpph*)(S) values of have been observed in alcohols. It is proposed that this is due to partial ionization of the phenols and a very fast electron transfer from phenoxide anion to dpph*. The popular assessment of the antioxidant activities of phenols with dpph* in alcohol solvents will generally lead to an overestimation of their activities.

404 citations


Journal ArticleDOI
TL;DR: Bismuth nitrate-catalyzed versatile Michael reaction was developed to reduce the complications that characterize the current standard Michael reaction and used for facile preparation of organic compounds of widely different structures.
Abstract: Bismuth nitrate-catalyzed versatile Michael reaction was developed to reduce the complications that characterize the current standard Michael reaction and used for facile preparation of organic compounds of widely different structures. For example, several substituted amines, imidazoles, thio compounds, indoles, and carbamates were prepared at room temperature by following this method. In contrast with the existing methods using many acidic catalysts, this method is very general, simple, high-yielding, environmentally friendly, and oxygen and moisture tolerant. However, the promoting role of bismuth nitrate in this reaction is not understood at this time.

365 citations


Journal ArticleDOI
TL;DR: An extended study of the reactivity of potassium aryl- and heteroaryltrifluoroborates in Suzuki-Miyaura cross-coupling reactions is presented, finding a low loading of PdCl(2)(dppf).
Abstract: An extended study of the reactivity of potassium aryl- and heteroaryltrifluoroborates in Suzuki-Miyaura cross-coupling reactions is presented. The coupling of aryl- and electron-rich heteroaryltrifluoroborates with aryl and activated heteroaryl bromides proceeds readily under ligandless conditions. When deactivated aryl- and heteroaryltrifluoroborates are coupled with aryl and heteroaryl bromides and chlorides, a low loading (0.5−2%) of PdCl2(dppf)·CH2Cl2 efficiently catalyzes the reactions. Under either condition, reactions can generally be carried out in an open atmosphere.

360 citations


Journal ArticleDOI
TL;DR: This methodology accommodates various alkynyl esters and has been successfully extended to the synthesis of polycyclic aromatic and biaryl compounds.
Abstract: A variety of substituted isocoumarins and α-pyrones are readily prepared in excellent yields under very mild reaction conditions by the reaction of o-(1-alkynyl)benzoates and (Z)-2-alken-4-ynoates with ICl, I2, PhSeCl, p-O2NC6H4SCl, and HI. This methodology accommodates various alkynyl esters and has been successfully extended to the synthesis of polycyclic aromatic and biaryl compounds.

308 citations


Journal ArticleDOI
TL;DR: The simplest binaphthyldiamino salen-type Zn complex gave the five-membered cyclic carbonate 2 in excellent yield in the presence of triethylamine using a Lewis acid and Lewis base cocatalyzed mechanism.
Abstract: Binaphthyldiamino salen-type Zn, Cu, and Co complexes can efficiently catalyze reactions of epoxides with carbon dioxide in the presence of various catalytic amounts of organic bases. The simplest binaphthyldiamino salen-type Zn complex gave the five-membered cyclic carbonate 2 in excellent yield in the presence of triethylamine. A Lewis acid and Lewis base cocatalyzed mechanism is proposed.

297 citations


Journal ArticleDOI
TL;DR: The fastest aminations of thiazoles, benzimidazoles, and benzoxazoles occurred with the combination of palladium trifluoroacetate and P(t)Bu(3) as catalyst.
Abstract: Detailed studies have been conducted to determine the activity of palladium catalysts for the amination of five-membered heterocyclic halides and to determine the factors that control the scope of this reaction. Palladium-catalyzed aminations of the electron-rich furanyl, thiophenyl, and indolyl halides and of the related 2-halogenated thiazoles, benzimidazole, and benzoxazole have been shown to occur with a subset of amines. Various combinations of palladium precursors and P(t)Bu(3) were tested as catalysts for reaction of 3-bromothiophene with N-methylaniline, and the fastest reactions occurred with the Pd(I) dimer, [PdBr(P(t)Bu(3))](2). The fastest aminations of thiazoles, benzimidazoles, and benzoxazoles occurred with the combination of palladium trifluoroacetate and P(t)Bu(3) as catalyst.

285 citations


Journal ArticleDOI
TL;DR: The structures of psammaplins E (9) and F (10), which each contain an oxalyl group rarely found in marine organisms, were determined by spectroscopic analysis and are potent histone deacetylase inhibitors and also show mild cytotoxicity.
Abstract: Four novel bisulfide bromotyrosine derivatives, psammaplins E (9), F (10), G (11), and H (12), and two new bromotyrosine derivatives, psammaplins I (13) and J (14), were isolated from the sponge Pseudoceratina purpurea, along with known psammaplins A (4), B (6), C (7), and D (8) and bisaprasin (5). The structures of psammaplins E (9) and F (10), which each contain an oxalyl group rarely found in marine organisms, were determined by spectroscopic analysis. Compounds 4, 5, and 10 are potent histone deacetylase inhibitors and also show mild cytotoxicity. Furthermore, compounds 4, 5, and 11 are potent DNA methyltransferase inhibitors. The biogenetic pathway previously proposed for the psammaplins class is also revisited.

271 citations


Journal ArticleDOI
TL;DR: On screening, 1-butylimidazolium tetrafluoroborate [Hbim]BF4 was found to be the best ionic liquid for the heteroannulation reaction, and the reasons to this effect are well explained.
Abstract: Several room-temperature ionic liquids (ILs) based on 1-butylimidazolium salts with varying anions were synthesized and evaluated for the preparation of biologically active substituted quinolines and fused polycyclic quinolines using the Friedlander heteroannulation reaction. On screening, 1-butylimidazolium tetrafluoroborate [Hbim]BF4 was found to be the best ionic liquid for the heteroannulation reaction, and the reasons to this effect are well explained. The reactions proceed very well under relatively mild conditions without any added catalyst. The IL acts as a promoter for this regiospecific synthesis and can be recycled. By this green approach, various quinolines were prepared in excellent yields and purity and well-characterized.

261 citations


Journal ArticleDOI
TL;DR: The FAM-labeled ssDNA was successfully used as a primer to produce DNA sequencing products with single-base resolution in a capillary electrophoresis DNA sequencer with laser-induced fluorescence detection.
Abstract: “Click chemistry” 1,3-dipolar cycloaddition between alkynyl 6-carboxyfluorescein (FAM) and azido-labeled single-stranded (ss) DNA was carried out under aqueous conditions to produce FAM-labeled ssDNA in quantitative yield. The FAM-labeled ssDNA was successfully used as a primer to produce DNA sequencing products with single-base resolution in a capillary electrophoresis DNA sequencer with laser-induced fluorescence detection.

260 citations


Journal ArticleDOI
TL;DR: Chiral 1,5-diaza-cis-decalins have been examined as ligands in the enantioselective oxidative biaryl coupling of substituted 2-naphthol derivatives and the relationship between the substitution of the naphthalene starting materials and reactivity/selectivity is determined.
Abstract: Chiral 1,5-diaza-cis-decalins have been examined as ligands in the enantioselective oxidative biaryl coupling of substituted 2-naphthol derivatives Under the optimal conditions employing 25-10 mol % of a 1,5-diaza-cis-decalin copper(II) catalyst with oxygen as the oxidant, enantioselective couplings (44-96% ee) could be achieved for a range of 3-substituted 2-naphthols including the ester, ketone, phosphonyl, and sulfonyl derivatives The relationship between the substitution of the naphthalene starting materials and reactivity/selectivity is determined by several factors which act in concert: (1) the effect of substituents on the oxidation potential of the substrate, (2) the ability of the substrate to participate in a chelated copper complex which depends on (a) the inherent coordinating ability of the 3-substituent and (b) substituent steric interactions that affect chelation between the 2-hydroxyl and 3-substituent, (3) the effect of substituents on dissociation of the product from the copper catalyst

Journal ArticleDOI
TL;DR: The reaction of N-vinylimidazole and diazo compounds derived from aldehydes gave exclusively 3-substituted pyrazoles in a one-pot process.
Abstract: A convenient one-pot procedure for the preparation of pyrazoles by 1,3-dipolar cycloaddition of diazo compounds generated in situ has been developed. Diazo compounds derived from aldehydes were reacted with terminal alkynes to furnish regioselectively 3,5-disubstituted pyrazoles. Furthermore, the reaction of N-vinylimidazole and diazo compounds derived from aldehydes gave exclusively 3-substituted pyrazoles in a one-pot process.

Journal ArticleDOI
TL;DR: This method provides an efficient and much improved modification of original Biginelli reaction reported in 1893, in terms of high yields, short reaction times, and simple work-up procedure, and it has the ability to tolerate a wide variety of substitutions in all three components, which is lacking in existing procedures.
Abstract: A general and practical green chemistry route to the Biginelli cyclocondensation reaction using cerium(III) chloride as the catalyst (25% mol) is described under three different sets of reaction conditions. This method provides an efficient and much improved modification of original Biginelli reaction reported in 1893, in terms of high yields, short reaction times, and simple work-up procedure, and it has the ability to tolerate a wide variety of substitutions in all three components, which is lacking in existing procedures.

Journal ArticleDOI
TL;DR: Palladium acetate was shown to be an extremely active catalyst for the Heck reaction of aryl bromides, with K(3)PO(4) and N,N-dimethylacetamide being the optimal base and solvent, respectively.
Abstract: Palladium acetate was shown to be an extremely active catalyst for the Heck reaction of aryl bromides. Both the base and the solvent were found to have a fundamental influence on the efficiency of the reaction, with K3PO4 and N,N-dimethylacetamide being the optimal base and solvent, respectively.

Journal ArticleDOI
TL;DR: The efforts in broadening the applicability of chiral pyrrolidine-based catalysts in direct asymmetric Mannich-type reactions led to the highly diastereo- and enantioselective and concise synthesis of functionalized alpha- and beta-amino acids, beta-lactams, and amino alcohols.
Abstract: The unprecedented application of unmodified aldehydes as nucleophilic donors in direct catalytic asymmetric Mannich-type reactions is disclosed in a full account. Our efforts in broadening the applicability of chiral pyrrolidine-based catalysts in direct asymmetric Mannich-type reactions led to the highly diastereo- and enantioselective and concise synthesis of functionalized α- and β-amino acids, β-lactams, and amino alcohols.

Journal ArticleDOI
TL;DR: For the first time, chiral imidazolium ionic liquids containing one chiral carbon (10a-c) were synthesized from the natural amino acids by a simple and straightforward procedure.
Abstract: For the first time, chiral imidazolium ionic liquids containing one chiral carbon (10a-c) were synthesized from the natural amino acids by a simple and straightforward procedure. The characteristics of the chiral ILs are very similar to the popular ionic liquids.

Journal ArticleDOI
TL;DR: Findings indicate that the H versus J aggregation mode of porphyrin stacks can be controlled by the peripheral hydrogen- bonding interactions and the microscopic hydrogen-bonding network structure is well-reflected by the macroscopic SEM-observed structure.
Abstract: To obtain insights into a correlation relationship between the structure and the aggregation mode in an organogel system, we synthesized gelators 2a−4a bearing a porphyrin moiety as a one-dimensional aggregation unit and amide groups as peripheral hydrogen-bonding sites. Gelators 3a and 3b bearing the amide groups at the 4-position of the meso-phenyl groups are classified as versatile gelators, gelating 10 and 14 solvents, respectively, among 23 solvents tested herein. In contrast, gelators 2a and 4a bearing the amide groups at the 3,5-positions and 3-position, respectively, are classified as poor gelators. Examination by spectroscopic methods (UV−vis, ATR−FTIR, XRD, etc.) revealed that in the organogel phase porphyrins in 3a adopt the H aggregation mode whereas those in 2a and 4a adopt the J aggregation mode. X-ray analysis of the single crystals established that in fact 3b features a columnar stack of porphyrin moieties that can be classified as the H-aggregate, whereas 2a results in a two-dimensional a...

Journal ArticleDOI
TL;DR: Kinetic studies, carried out in order to better understand the mechanism of the NHPI-catalyzed aerobic oxidation of cumene, are consistent with a simple kinetic model where the rate-determining step is the hydrogen atom abstraction from the hydroxylamine by cumylperoxyl radicals.
Abstract: Bond dissociation enthalpies (BDE) of hydroxylamines containing alkyl, aryl, vinyl, and carbonyl substituents at the nitrogen atom have been determined by using the EPR radical equilibration technique in order to study the effect of the substituents on the O-H bond strength of these compounds. It has been found that substitution of an alkyl group directly bonded to the nitrogen atom with vinyl or aryl groups has a small effect, while substitution with acyl groups induces a large increase of the O-H BDE value. Thus, dialkyl hydroxylamines have O-H bond strengths of only ca. 70 kcal/mol, while acylhydroxylamines and N-hydroxyphthalimide (NHPI), containing two acyl substituents at nitrogen, are characterized by BDE values of ca. 80 and 88 kcal/mol, respectively. Since the phthalimide N-oxyl radical (PINO) has been recently proposed as an efficient oxidation catalyst of hydrocarbons or other substrates, the large BDE value found for the parent hydroxylamine (NHPI) justifies this proposal. Kinetic studies, carried out in order to better understand the mechanism of the NHPI-catalyzed aerobic oxidation of cumene, are consistent with a simple kinetic model where the rate-determining step is the hydrogen atom abstraction from the hydroxylamine by cumylperoxyl radicals.

Journal ArticleDOI
TL;DR: It is possible to prepare biaryls in good yield very rapidy on small and larger scales from aryl halides and phenylboronic acid using water as a solvent and palladium acetate as catalyst.
Abstract: It is possible to prepare biaryls in good yield very rapidy (5-10 min) on small (1 mmol) and larger (10-20 mmol) scales from aryl halides and phenylboronic acid using water as a solvent and palladium acetate as catalyst. The reaction can be performed equally well using microwave and conventional heating, showing that using these conditions probably no nonthermal microwave effects are associated with the impressive speed of the reaction.

Journal ArticleDOI
TL;DR: In the presence of catalytic amounts of sodium iodide, triphenylphosphine, and phenol, carbon dioxide can efficiently react with epoxides to give the corresponding five-membered cyclic carbonates in high yields.
Abstract: In the presence of catalytic amounts of sodium iodide, triphenylphosphine, and phenol, carbon dioxide can efficiently react with epoxides to give the corresponding five-membered cyclic carbonates in high yields. The mechanism of this reaction was disclosed by (31)P NMR spectroscopic data and deuterium labeling experiments.

Journal ArticleDOI
TL;DR: The NHC-catalyzed transesterification protocol was simplified by generating the imidazol-2-ylidene catalysts in situ, and methyl and ethyl esters can be employed as protective agents for secondary alcohols in the presence of the more active alkyl-substituted NHC catalysts.
Abstract: Imidazol-2-ylidenes, a family of N-heterocyclic carbenes (NHC), are efficient catalysts in the transesterification involving numerous esters and alcohols. Low catalyst loadings of aryl- or alkyl-substituted NHC catalysts mediate the acylation of alcohols with enol acetates in short reaction times at room temperature. Commercially available and more difficult to cleave methyl esters react with primary alcohols in the presence of alkyl-substituted NHC to efficiently form the corresponding esters. While primary alcohols are selectively acylated over secondary alcohols with use of enol esters as acylating agents, methyl and ethyl esters can be employed as protective agents for secondary alcohols in the presence of the more active alkyl-substituted NHC catalysts. The NHC-catalyzed transesterification protocol was simplified by generating the imidazol-2-ylidene catalysts in situ.

Journal ArticleDOI
TL;DR: Functionalized vinyl pinacol boronates suitable for Suzuki cross-coupling reactions are synthesized using ruthenium-catalyzed olefin cross-metathesis of 1-propenyl pinacols and variousAlkenes, including functionalized and 1,1-disubstituted alkenes.
Abstract: Functionalized vinyl pinacol boronates suitable for Suzuki cross-coupling reactions are synthesized using ruthenium-catalyzed olefin cross-metathesis of 1-propenyl pinacol boronate and various alkenes, including functionalized and 1,1-disubstituted alkenes. The resultant boronate cross products are stereoselectively transformed into predominantly Z-vinyl bromides and E-vinyl iodides. The vinyl bromides may be synthesized in a two-step, one-pot synthesis from a variety of olefins, resulting in a Z-selective formal vinyl bromide cross-metathesis reaction.

Journal ArticleDOI
TL;DR: This Perspective discusses the development of one such tandem reaction, the acid-promoted (or catalyzed) Prins-pinacol rearrangement, with particular emphasis on its implementation as the key strategic element in the total synthesis of heterocyclic and carbocyclics natural products.
Abstract: An important objective of contemporary synthesis endeavors is the development of new transformations that rapidly evolve molecular complexity in a stereocontrolled fashion. One approach toward this goal is to combine two or more distinct reactions into a single transformation, producing a process often referred to as a sequential, tandem, cascade, or domino reaction. In this Perspective, we discuss the development of one such tandem reaction, the acid-promoted (or catalyzed) Prins−pinacol rearrangement, with particular emphasis on its implementation as the key strategic element in the total synthesis of heterocyclic and carbocyclic natural products.

Journal ArticleDOI
TL;DR: An improved microwave protocol, relying on DBU as base and THF as solvent, enables rapid couplings using otherwise sluggish anilines, tert-butylamine, and free amino acids.
Abstract: Commercially available molybdenum hexacarbonyl serves as a convenient and solid carbon monoxide source in palladium-catalyzed aminocarbonylations of aryl bromides and iodides. This improved microwave protocol, relying on DBU as base and THF as solvent, enables rapid couplings using otherwise sluggish anilines, tert-butylamine, and free amino acids. In addition, Cr(CO)6 and W(CO)6 were found to be useful alternative CO-releasing reagents. Altogether, 16 different aromatic amides were synthesized under air in 35−95% yield after only 15 min of controlled microwave irradiation.

Journal ArticleDOI
TL;DR: The present reaction is chemically equivalent to the transition metal-catalyzed cyclopropanation reaction using alpha-diazoketones as carbenoid precursors.
Abstract: Intermolecular cyclopropanation reactions of various alkenes with propargylic carboxylates 1 are catalyzed by [RuCl2(CO)3]2 to give vinylcyclopropanes 2 in good yields. The key intermediate of the reaction is a vinylcarbene complex generated in situ by nucleophilic attack of a carbonyl oxygen of the carboxylates to an internal carbon of the alkyne activated by the ruthenium complex. A variety of transition-metal compounds other than the Ru compound can also be employed in this system. Similar cyclopropanation proceeds with conjugated dienes as well to give trans-vic-divinylcyclopropane derivatives and cycloheptadiene derivatives 5, the latter being thermally derived from the initially formed cis-vic-isomers via Cope-type rearrangement. The present reaction is chemically equivalent to the transition metal-catalyzed cyclopropanation reaction using α-diazoketones as carbenoid precursors.

Journal ArticleDOI
TL;DR: The combination of a secondary benzyl alcohol and a metal triflate in nitromethane was a highly effective secondary-benzylation system and trifluoromethanesulfonic acid (triflic acid, TfOH) was also a good catalyst.
Abstract: The combination of a secondary benzyl alcohol and a metal triflate (e.g., La, Yb, Sc, and Hf triflate) in nitromethane was a highly effective secondary-benzylation system. Secondary benzylation of carbon (aromatic compounds, olefins, an enol acetate), nitrogen (amide derivatives), and oxygen (alcohols) nucleophiles was carried out with a secondary benzyl alcohol and 0.01−1 mol % of a metal triflate in the presence of water. Secondary benzyl alcohols and nucleophiles bearing acid-sensitive functional groups (e.g., tert-butyldimethylsilyloxy and acetoxy groups and methyl and benzyl esters) could be used for alkylation. Hf(OTf)4 was the most active catalyst for this alkylation, and trifluoromethanesulfonic acid (triflic acid, TfOH) was also a good catalyst. The catalytic activity of metal triflates and TfOH increased in the order La(OTf)3 < Yb(OTf)3 < TfOH < Sc(OTf)3 < Hf(OTf)4. A mechanistic study was also performed. The reaction of 1-phenylethanol (4a) in the presence of Sc(OTf)3 in nitromethane gave an eq...

Journal ArticleDOI
TL;DR: Different features of DNA charge transport chemistry are discussed, including applications as well as possible biological consequences and opportunities, according to sequence-dependent DNA structure and dynamics.
Abstract: The stack of base pairs within double helical DNA has been shown to mediate charge transport reactions. Charge transport through DNA can result in chemistry at a distance, yielding oxidative DNA damage at a site remote from the bound oxidant. Since DNA charge transport chemistry depends on coupling within the stacked base pair array, this chemistry is remarkably sensitive to sequence-dependent DNA structure and dynamics. Here, we discuss different features of DNA charge transport chemistry, including applications as well as possible biological consequences and opportunities.

Journal ArticleDOI
TL;DR: The reaction profile with quinuclidine showed significant autocatalysis, which suggested that the presence of proton donors might further enhance rates, and a series of additives bearing polar X-H bonds were investigated and it was found that methanol, triethanolamine, formamide, and water all provided additional acceleration.
Abstract: The reactivity of a variety of quinuclidine-based catalysts in the Baylis−Hillman reaction has been examined, and a straightforward correlation between the basicity of the base and reactivity has been established, without exception. The following order of reactivity was established with pKa's of the conjugate acids (measured in water) given in parentheses: quinuclidine (11.3), 3-hydroxyquinuclidine (9.9), DABCO (8.7), 3-acetoxyquinuclidine (9.3), 3-chloroquinuclidine (8.9), and quinuclidinone (7.2). The higher than expected reactivity of DABCO, based on its pKa, was analyzed by comparing the relative basicity of DABCO and 3-acetoxyquinuclidine in DMSO. It was found that in aprotic solvent, DABCO was 0.6 pKa units more basic than 3-acetoxyquinuclidine, thus establishing a direct link between pKa of the amine and its reactivity. In contrast to previous literature work that reported the contrary, quinuclidine, which has the highest pKa, was found to be the most active catalyst. The reaction profile with qui...

Journal ArticleDOI
TL;DR: This work has identified a three-state molecular switch that responds to one chemical and two optical inputs producing two optical outputs and encoded binary digits in its inputs and outputs applying positive logic conventions and demonstrated that this chemical system converts three-digit input strings into two-digit output strings.
Abstract: Certain molecular switches respond to input stimulations producing detectable outputs. The interplay of these signals can be exploited to reproduce basic logic operations at the molecular level. The transition from simple logic gates to complex digital circuits requires the design of chemical systems able to process multiple inputs and outputs. We have identified a three-state molecular switch that responds to one chemical and two optical inputs producing two optical outputs. We have encoded binary digits in its inputs and outputs applying positive logic conventions and demonstrated that this chemical system converts three-digit input strings into two-digit output strings. The logic function executed by the three-state molecular switch is equivalent to that of a combinational logic circuit integrating two AND, two NOT, and one OR gate. The three states of the molecular switch are a colorless spiropyran, a purple trans-merocyanine, and its yellow-green protonated form. We have elucidated their structures b...

Journal ArticleDOI
TL;DR: The use of rhodium catalysts with PiPr2(OAr) or P(NMe2)3 co-catalysts allows the ortho-selective intermolecular arylation of phenols through orthometalation of P-OAr groups and then transesterification liberates the product phenol.
Abstract: The use of rhodium catalysts such as [RhCl(PPh3)3] or [{RhCl(COD)}2] with PiPr2(OAr) or P(NMe2)3 co-catalysts allows the ortho-selective intermolecular arylation of phenols. The reaction proceeds via orthometalation of P-OAr groups and then transesterification liberates the product phenol. When 2-substituted phenols are used as substrates, [RhCl(PPh3)3]/iPr2(OAr) mixtures are typically the catalysts of choice, whereas for substrates without 2-substitution [{RhCl(COD)}2]/P(NMe2)3 mixtures tend to give better results.