Diaryl Methyl Research Articles

Dirhodium‐Catalyzed Enantioselective B−H Bond Insertion of gem‐Diaryl Carbenes: Efficient Access to gem‐Diarylmethine Boranes

AbstractThe scarcity of reliable methods for synthesizing chiral gem‐diarylmethine borons limits their applications. Herein, we report a method for highly enantioselective dirhodium‐catalyzed B−H bond insertion reactions with diaryl diazomethanes as carbene precursors. These reactions afforded chiral gem‐diarylmethine borane compounds in high yield (up to 99 % yield), high activity (turnover numbers up to 14 300), high enantioselectivity (up to 99 % ee) and showed unprecedented broad functional group tolerance. The borane compounds synthesized by this method could be efficiently transformed into diaryl methanol, diaryl methyl amine, and triaryl methane derivatives with good stereospecificity. Mechanistic studies suggested that the borane adduct coordinated to the rhodium catalyst and thus interfered with decomposition of the diazomethane, and that insertion of a rhodium carbene (generated from the diaryl diazomethane) into the B−H bond was most likely the rate‐determining step.

Dirhodium-Catalyzed Enantioselective B-H Bond Insertion of gem-Diaryl Carbenes: Efficient Access to gem-Diarylmethine Boranes.

The scarcity of reliable methods for synthesizing chiral gem-diarylmethine borons limits their applications. Herein, we report a method for highly enantioselective dirhodium-catalyzed B-H bond insertion reactions with diaryl diazomethanes as carbene precursors. These reactions afforded chiral gem-diarylmethine borane compounds in high yield (up to 99 % yield), high activity (turnover numbers up to 14 300), high enantioselectivity (up to 99 % ee) and showed unprecedented broad functional group tolerance. The borane compounds synthesized by this method could be efficiently transformed into diaryl methanol, diaryl methyl amine, and triaryl methane derivatives with good stereospecificity. Mechanistic studies suggested that the borane adduct coordinated to the rhodium catalyst and thus interfered with decomposition of the diazomethane, and that insertion of a rhodium carbene (generated from the diaryl diazomethane) into the B-H bond was most likely the rate-determining step.

Metal free highly efficient C–N bond formation through 1,6-addition: synthesis and photophysical studies of diaryl methyl amino acid esters (DMAAEs)

A transition-metal free, proficient strategy for the one-pot synthesis of diverse diaryl methyl amino acid esters (DMAAEs) has been established from the easily accessible chiral amino acid esters and para-quinone methides (QMs) in very good to excellent yields.

Transition-metal-free phenylselenylation of arenes with triflic anhydride activated methyl phenyl selenoxide

Phenylselenylation of arenes were achieved in a one-pot procedure by treating arene substrates with triflic anhydride activated methyl phenyl selenoxide, and then demethylation with diisopropylamine. This reaction provide a convenient method to prepare diarylselenide products under transition-metal-free conditions. • Highly electrophilic selenium reagent was generated from selenoxide and triflic anhydride. • The substitution reaction with such selenium reagent proceed with innate regioselectivity of the aromatic ring. • Demethylation of diaryl methyl selenonium salt is accomplished with diisopropylamine.

Carbene-catalyzed enantioselective oxidative coupling of enals and di(hetero)arylmethanes.

Di(hetero)arylmethane is a unique structural motif for natural and synthetic functional molecules. To date, it remains challenging to functionalize the diaryl methyl sp3 carbon-hydrogen bond directly in an enantioselective manner. This is likely due to the relatively inert nature of the carbon-hydrogen bond and the difficult enantiofacial discrimination of two sterically similar aryl substituents. Here we disclose an N-heterocyclic carbene-catalyzed direct oxidative coupling of enals and di(hetero)arylmethanes. Our method allows for highly enantioselective transformation of diaryl methanes and quick access to benzimidazole fused lactams.

Efficient access to triarylmethanes through decarboxylation

A new approach has been developed for diverse triarylmethanes by palladium catalyzed decarboxylative sp2–sp3 cross coupling where benzoic acids reacted with diaryl methyl iodides having both electron donating and withdrawing functionalities.

Oligomerization of higher olefins and alkylation of toluene catalyzed by 2-[hydroxy(diaryl)methyl]-8-hydroxyquinoline oxovanadium(v) complexes

New oxovanadium(V) complexes with 2-[hydroxy(diaryl)methyl]-8-hydroxyquinoline ligands were synthesized. These compounds were found to be efficient tandem catalysts of oligomerization of hex-1-ene and alkylation of toluene, which leads to the mixture of hexyl-, dihexyl-, and trihexyltoluenes with the conversion of the starting alkene more than 99%.

Stereoselective synthesis of 1,3-disubstituted phthalans by cyclization of (1S)-1-{2-[hydroxy(diaryl)methyl]phenyl}ethanols

Cyclization of pure enantiomers of 1-{2-[hydroxy(diaryl)methyl]phenyl}ethanol proceeds stereoselectively and affords 1,3-disubstituted 1,3-dihydroisobenzofurans (phthalans) in moderate-to-high enantiomeric (81.7% ee) or diastereomeric (72% de) purity.

Intermolecular reductive coupling of esters with benzophenones by low-valent titanium: synthesis of diarylmethyl ketones revisited.

The reductive coupling of aliphatic esters with benzophenones by Zn-TiCl4 in THF gave two- and four-electron reduced products, diaryl(hydroxy)methyl ketones, and diarylmethyl ketones selectively by controlling the reaction conditions. In the reaction of aromatic esters with benzophenones, diarylmethyl ketones were obtained as the sole products. N-(Alkoxycarbonyl)-(S)-α-amino acid methyl esters gave optically active diphenylmethyl ketones by reduction with benzophenone. The obtained diphenylmethyl ketones were transformed to 4,5-cis-disubstituted oxazolidin-2-ones stereoselectively.

Enantioselective fluorination of β-ketoesters catalysed by complexes of new mono-oxazoline ligands

A new kind of mono-oxazoline ligands which combined diaryl methyl units and chiral oxazoline units together using pyridine as linker was prepared. Their applications in enantioselective electrophilic fluorination of β-ketoesters by NFSI were investigated, and the corresponding products were obtained in excellent yield (up to 90%) and good enantioselectivity (78%) in CH2Cl2 at −60 °C.

ChemInform Abstract: The Diaryl(oxy)methyl Group: More than an Innocent Bystander in Chiral Auxiliaries, Catalyst, and Dopants.

AbstractReview: ca. 200 refs.

The Diaryl(oxy)methyl Group: More than an Innocent Bystander in Chiral Auxiliaries, Catalysts, and Dopants

Either as the free alcohol or deprotonated, a carbinol residue bearing gemial, identical aryl residues can at first sight be recognized as an achiral structural unit. When incorporated, however, into a chiral molecule, the two aryl groups become diastereotopic. Thus, they might contribute to an enhancement in stereoselectivity and do so in a variety of reactions. This Minireview highlights developments in stereochemistry when the diaryl(oxy)methyl group is involved, with emphasis given to the beneficial effect of this moiety. Of particular focus are auxiliaries, the stoichiometric use of metal complexes, metal and organocatalysts, and finally chiral dopants for liquid crystals, all featuring the diaryl(oxy)methyl group.

ChemInform Abstract: Broensted Acid Catalyzed α‐Alkylation of Aldehydes with Diaryl Methyl Alcohols.

AbstractThe α‐alkylation of aldehydes with diarylmethanols is achieved in the presence of Broensted acids such as TfOH, TosOH or dinitrobenzenesulfonic acid.

Brønsted Acid Catalyzed α‐Alkylation of Aldehydes with Diaryl Methyl Alcohols

The catalytic a-alkylation of carbonyl compounds is a common approach in organic synthesis. In recent years, many efforts have been directed towards the activation of ketones and aldehydes by means of enamine catalysis to react with a broad range of electrophiles. In 2004, List reported an elegant intramolecular alkylation of aldehydes with alkyl halides using proline-based amine catalysts. While the long-sought intermolecular versions of such enamine-catalytic SN2-type a-alkylation of aldehydes [3] remain challenging, research by the groups of Melchiorre, Cozzi, Jacobsen and others have pioneered the amine-mediated SN1type intermolecular reactions between aldehydes and arylsulfonyl indoles, diaryl alcohols, or halides. In the approach used by Cozzi and others, amine catalysts were used to activate the aldehydes via enamine intermediates, and Bronsted acids were used to mediate the formation of diaryl methyl cations from the corresponding diaryl methanols. Despite the success of this amine/acid co-catalysis approach for diaryl methyl alcohols (e.g., 1a) that generate highly stabilized carbocations, the scope of the reactions still remains limited: diaryl methyl alcohols (such as 1b–f) that lead to “less stabilized” diaryl methyl carbocation electrophiles are ineffective substrates in these alkylation reactions. Instead of using enamine catalysis for aldehyde activation, here we disclose the use of Bronsted acids alone to catalyze these SN1 type aldehyde alkylations. The acid catalyst is believed to facilitate the formation of alcohol-derived carbocations and to accelerate the enolization of aldehydes. A much broader scope of substrates is thereby realized: diaryl methyl alcohols that lead to less stabilized carbocations can be used; aldehydes with a,a-disubstituents react efficiently as well to generate products containing quaternary carbon centers. Our work began by using diaryl methanol 1b as a model substrate to develop an acid-catalysis approach. According to the Mayr reactivity scales, such substrates lead to lessstabilized carbocations (e.g., compared to that from 1a) and were ineffective using the enamine/acid co-catalytic strategies. The results of our initial studies are summarized in Table 1. Weak acids, such as acetic acid, could not mediate

Regioselective Synthesis of 1‐Allyl‐ and 1‐Arylmethyl Uracil and Thymine Derivatives.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Regioselective synthesis of 1-allyl- and 1-arylmethyl uracil and thymine derivatives

2,4-Bis(trimethylsiloxy) pyrimidines 1 with allyl halides and arylmethyl halides in 1,2-dichloroethane in the presence of I 2 regioselectively provide 1-allyl-/1-arylmethyl-uracil and thymine derivatives. The secondary aryl alkyl and diaryl methyl halides with 1 provide chiral 1-arylalkyl/1-(diarylmethyl) uracil/thymine derivatives. The procedure has been extended to the synthesis of fluorescent uracil/thymine derivatives.

Novel Heteroatom-Linked Analogues of Trityl Radicals: Diaryl(benzotriazol-1-yl)methyl Radical Dimers

The lithiation of diaryl(benzotriazol-1-yl)methanes followed by addition of iodine generates phenanthridines and dimers of hitherto unknown trityl analogues in which the radical center is directly attached to a heteroatom. These dimers differ from those of triarylmethyl radicals by not dissociating in solution, but variable temperature ESR measurements provided direct evidence for the formation of the corresponding diaryl(benzotriazol-1-yl)methyl radicals as intermediates in solution.

ELECTRONIC STRUCTURE AND 31P NMR CHEMICAL SHIFT OF SUBSTITUTED TRIARYL, DIARYL METHYL AND DIMETHYL ARYL PHOSPHATES-A SEMI-EMPIRICAL MOLECULAR ORBITAL APPROACH

The 31P NMR chemical shift of triaryl phosphate, diaryl methyl phosphate and dimethyl aryl phosphate series was determined. The δ31P values exhibit an increasing downfield trend when aryl substituents are exchanged for alkyl groups and δ31P values show an increasing upfield trend as the electron-withdrawing ability of the substituent in the aromatic ring is increased. Semi-empirical calculations showed an increasing positive charge on phosphorus atom and an increasing phosphoryl bond order when δ31P values go upfield. These results are in agreement with the effect of “back bonding” from the phosphoryl oxygen to the phosphorus atom.

ChemInform Abstract: Synthesis and Antimicrobial Activity of Methyl and Phenyl Diarylmethyl Ketones.

AbstractThe diaryl methyl ketones (III) are prepared from the lactic‐ or mandelic acid esters (I) and the Grignard reagents (II).

Biomimetic methyl transfer to olefins

Conditions have been found under which trisubstituted olefins can be methylated with diaryl methyl sulfonium salts in 2,6-di- t -butylpyridine. The pattern of methylated compound's formed is similar to that of the enzymatic methylation of Δ 24 steroids side chains with S -adenosylmethionine as a methyl donor.