Unsymmetrical Benzils Research Articles

I2-Mediated Site-Selective C-H Functionalization: Access to p-Amino-Substituted Unsymmetrical Benzils and Quinoxalines from Sulfoxonium Ylides.

An I2-mediated approach for selective C-H functionalization of unprotected aniline derivatives for synthesizing benzils and quinoxaline derivatives from sulfoxonium ylides has been described. Aniline derivatives and sulfoxonium ylides ornamented with different functional groups showed good compatibility. They afforded the corresponding products with moderate to high yields via a mild and simple procedure. Finally, we validated the practicality of this method by scaling up the reaction and further conversion of the synthesized derivatives into other valuable molecules.

Synthesis of unsymmetrical benzils via palladium-catalysed α-arylation-oxidation of 2-hydroxyacetophenones with aryl bromides.

A diverse set of unsymmetrically substituted benzils were facilely synthesised by a cross-coupling reaction between 2-hydroxyacetophenones and aryl bromides in the presence of a palladium catalyst. Experimental studies suggested a reaction mechanism involving a one-pot tandem palladium-catalysed α-arylation and oxidation, where aryl bromides play a dual role as mild oxidants as well as arylating agents.

Reductive (3 + 2) Annulation of Benzils with Pyrylium Salts: Stereoselective Access to Furyl Analogues of cis-Chalcones.

An unprecedented reductive (3 + 2) annulation of both symmetrical and unsymmetrical benzils with pyrylium salts mediated by P(NMe2)3 is described, leading to facile and stereoselective access to the challenging cis-chalcones decorated by various substituted furyl rings under mild conditions. Rather than the extensively studied C1 synthons, the Kukhtin-Ramirez adducts derived from benzils serve as the underexplored C3 synthons in this (3 + 2) annulation with the 2,3-double bond of the 2,6-disubstituted pyrylium ions.

One‐Pot Synthesis of p‐Amino‐Substituted Unsymmetrical Benzils and Benzil Derivatives

AbstractAn efficient iodine/copper(II) oxide co‐promoted direct oxidative coupling of anilines and methyl aryl ketones has been developed for the synthesis of p‐amino‐substituted unsymmetrical benzils and their iodo‐substituted derivatives. The chemoselectivity of the reactions can be easily controlled by adjusting the amount of iodine. This method exhibits good functional group tolerance for various substituents on the aromatic rings of the methyl aryl ketones. A possible mechanism for this reaction has been proposed based on control experiments. A couple of representative quinoxalines were synthesized from the benzil products in order to demonstrate the utility of this approach.magnified image

ChemInform Abstract: Asymmetric Transfer Hydrogenation of Unsymmetrical Benzils.

In this paper, the asymmetric transfer hydrogenation of unsymmetrical benzils with m, p-substituents was conducted with a substrate/catalyst molar ratio of 100 at 40 °C for 24 h to produce (S,S)-hydrobenzoins in good yields (76.2% to 97.1%) with high diastereomeric (syn/anti = 10.8 to 29.7/1) and enantiomeric purities (86.1%ee syn to 98.9%ee syn). Unfortunately, the unsymmetrical benzils with the o-substituents such as electron-donating (R = CH3, OCH3) and electron-withdrawing groups (R = F, Cl, CF3) resulted in poor yields (0% to 31.2%), even at 40 °C for 72 h. These products had inefficient diastereoselectivities (syn/anti = 1.5 to 5.0/1) caused by steric effects. Furthermore, the results of a dynamic–kinetic study were used to propose a plausible reaction pathway of unsymmetrical benzil using 3-methoxy-1,2-diphenyl ethanedione as an example.

The enhanced asymmetric hydrogenation of unsymmetrical benzils to hydrobenzoin catalyzed by organosoluble zirconium phosphonate-immobilized ruthenium catalyst

In this article, a successful design on translating a heterogeneous catalysis of chiral zirconium phosphonate-supported ruthenium catalyst into a homogeneous system was developed by the covalent attachment of chiral (R,R)-1,2-diphenyl-ethylenediamine [(R,R)-DPEN] into the backbone of zirconium phosphonate with the different arm lengths (n=2, 4, 6) and immobilization of [RuCl2(p-cymene)]2. Their catalytic performances in the homogeneous asymmetric transfer hydrogenation of unsymmetrical benzils with m- and p-substituents were enhanced, and the excellent activities (>97.1% conv.), diastereomeric and enantiomeric purities (syn/anti=11.0–29.4, 91.8–99.2%ee syn) were achieved. These homogeneous supported Ru catalysts could be quantitatively and readily recovered by addition of ethyl acetate and centrifugation by solid/liquid separation, and be reused for five times without significant loss of their catalytic performances with 97.0% conv., 95.6% syn and syn/anti=20.7.

Total Synthesis of Unsymmetrical Benzils, Scandione and Calophione A

AbstractThe synthesis of the title unsymmetrical benzils, scandione and calophione A, is described. The key processes involve intramolecular cyclization reaction of the carbanion at the benzylic position of the arylbenzyl ether to the adjacent ester group followed by oxidation. The palladium(II)‐catalyzed oxidative cyclization was also used to establish the benzofuran unit of calophione A.

Asymmetric transfer hydrogenation of unsymmetrical benzils

In this paper, the asymmetric transfer hydrogenation of unsymmetrical benzils with m, p-substituents was conducted with a substrate/catalyst molar ratio of 100 at 40 °C for 24 h to produce (S,S)-hydrobenzoins in good yields (76.2% to 97.1%) with high diastereomeric (syn/anti = 10.8 to 29.7/1) and enantiomeric purities (86.1%ee syn to 98.9%ee syn). Unfortunately, the unsymmetrical benzils with the o-substituents such as electron-donating (R = CH3, OCH3) and electron-withdrawing groups (R = F, Cl, CF3) resulted in poor yields (0% to 31.2%), even at 40 °C for 72 h. These products had inefficient diastereoselectivities (syn/anti = 1.5 to 5.0/1) caused by steric effects. Furthermore, the results of a dynamic–kinetic study were used to propose a plausible reaction pathway of unsymmetrical benzil using 3-methoxy-1,2-diphenyl ethanedione as an example.

ChemInform Abstract: One‐Pot Synthesis of Unsymmetrical Benzils and N‐Heteroarenes Through Nucleophilic Aroylation Catalyzed by N‐Heterocyclic Carbene.

AbstractN‐phenylbenzimidoyl chlorides (I) are readily obtained by chlorination of benzanilides.The method is applied to the synthesis of quinoxalines (IV) and pyrazines (VII).

One-pot synthesis of unsymmetrical benzils and N-heteroarenes through nucleophilic aroylation catalyzed by N-heterocyclic carbene

An efficient one-pot synthesis of various unsymmetrical benzils via N-heterocyclic carbene (NHC)-catalyzed aroylation of N-phenylimidoyl chlorides with aromatic aldehydes followed by acidic hydrolysis has been developed. The one-pot procedure was extended to synthesis of quinoxalines and pyrazines by condensation/annulation of unsymmetrical benzils generated in situ with diamines.

ChemInform Abstract: One‐Pot Synthesis of Unsymmetrical Benzils from Aryl Methyl Ketones and Arenes in the Presence of Selenous Acid Catalyzed by p‐Toluenesulfonic Acid Monohydrate.

AbstractA modified process is presented for the oxidative coupling of acetophenones with weakly or unactivated arenes to produce the synthetically important benzil structures.

One-pot synthesis of unsymmetrical benzils from aryl methyl ketones and arenes in the presence of selenous acid catalysed by p-toluenesulfonic acid monohydrate

A modified one-pot method for the synthesis of unsymmetrical and heteroaryl benzils from substituted acetophenones and unactivated or weakly activated arenes by the use of H2SeO3 and p-TsOH·H2O as catalysts at 35°C is established. The present method is regioselective and avoids the use of p-TsOH·H2O in stoichiometric amount in the presence of H2SeO3 and afforded unsymmetrical benzils in good yields.

One‐Pot Synthesis of Unsymmetrical Benzils by Oxidative Coupling Using Selenium Dioxide and p‐Toluenesulfonic Acid Monohydrate

AbstractThe oxidative coupling of the α‐carbon atom of aromatic ketones with unactivated arenes in the presence of selenium dioxide and p‐toluenesulfonic acid monohydrate is described. A number of unsymmetrical benzils have been prepared in good yields (38–75 %) with high regioselectivity. The generality and functional tolerance of this new protocol is demonstrated. The mechanistic pathway for the oxidative coupling reaction is also described. The reaction displays superiority in terms of minimization of steps with the C–C bond formation promoted by SeO2 and pTsOH·H2O. This method is advantageous as the reactants used as the solvent can be recovered.

Synthesis of unsymmetrical benzils using N-heterocyclic carbene catalysis

In this paper, we propose a novel and efficient method for the preparation of various unsymmetrical benzils. We first demonstrate the nucleophilic aroylation of N-phenylbenzimidoyl chlorides with aromatic aldehydes using N-heterocyclic carbene as the catalyst to afford 1-aryl-2-phenyl-2-(phenylimino)ethanones. These iminoethanones were then converted to 1,2-diaryl-1,2-diketones by acid-promoted hydrolysis.

Ultrasound‐enhanced Green Synthesis of 5,5‐Diphenylhydantoin Derivatives Using Symmetrical or Unsymmetrical Benzils

AbstractA rapid, highly efficient and mild green synthesis of 5,5‐diphenylhydantoin derivatives was achieved from the reaction of symmetrical or unsymmetrical benzil derivatives with urea in the presence of ethanolic KOH under ultrasound irradiation. This simple method affords 5,5‐diphenylhydantoin derivatives at room temperature in short reaction time with high yield and purity. This study aimed to overcome the limitations and drawbacks of the reported methods such as tedious work‐up, low yield and long reaction time.

Palladium‐catalyzed arylation of arylglyoxals with arylboronic acids

AbstractA palladium‐catalyzed coupling‐type reaction of arylglyoxals with arylboronic acids was achieved by use of trimesitylphosphine as the ligand and K2CO3 as base in toluene, providing symmetrical and unsymmetrical benzil derivatives with yields ranging from moderate to excellent. Of particular mention, the rigorous exclusion of air and moisture is not required in these transformations. Copyright © 2009 John Wiley & Sons, Ltd.

CONVENIENT PREPARATION OF UNSYMMETRICALLY SUBSTITUTED BENZILS BY PERMANGANATE OXIDATION OF β-OXO PHOSPHORUS YLIDES

Abstract Oxidative cleavage of a range of ylides 4 with R1 and/or R2 being aromatic groups, using KMnO4 in a two-phase system, affords unsymmetrical benzils and 1-arylpropane-1,2-diones 5 in moderate to good yield, and the ylide formation and oxidation can be combined in a convenient one-pot method.

THE REACTION OF SOME SUBSTITUTED BENZILS AND HETEROCYCLIC ANALOGS WITH CHLOROSULFONIC ACID

Abstract The chlorosulfonation of a number of unsymmetrical benzils gave substituted benzofurans. Ring closure is dependent upon the electronic character of the substituent groups and can be controlled by electron-withdrawing groups. The reaction of the 2-thienyl analog gave one product but the 3-thienyl compound gave a mixture of isomers. The previously proposed mechanism can be used to explain these results.

Facile oxidation of o-hydroxyphenyl benzyl ketones to unsymmetrical benzils with dimethyl sulphoxide/potassium hydroxide

o-Hydroxyphenyl benzyl ketones on treatment with dimethyl sulphoxide and powdered potassium hydroxide have been found to undergo facile oxidation to the corresponding benzils.

ChemInform Abstract: PHOTOLYSIS OF IMIDAZOLE N(3)‐OXIDES. FORMATION OF UNSYMMETRICAL BENZIL DI‐IMINES; X‐RAY CRYSTAL STRUCTURE OF ONE SUCH DI‐IMINE

AbstractDie Belichtung der N‐Oxide (I) ergibt in verd. Methanol, Aceton oder Benzol über die Zwischenstufen (II) die unsymmetrischen Benzildiimine (III).