27739-61-3Relevant academic research and scientific papers
Reactions of ZnR2 compounds with dibenzoyl: Characterisation of the alkyl-transfer products and a striking product-inhibition effect
Dranka, Izabela,Kubisiak, Marcin,Justyniak, Iwona,Lesiuk, Micha?,Kubicki, Dominik,Lewiński, Janusz
, p. 12713 - 12721 (2011)
The first systematic theoretical and experimental studies of reaction systems involving ZnR2 (R=Me, Et or tBu) with dibenzoyl (dbz) as a non-innocent ligand revealed that the character of the metal-bonded R group as well as the ratio of the reagents and the reaction temperature significantly modulate the reaction outcome. DFT calculations showed four stable minima for initial complexes formed between ZnR2 and dbz and the most stable structure proved to be the 2:1 adduct; among the 1:1 adducts three structural isomers were found of which the most stable complex had the monodentate coordination mode and the chelate complex with the s-cis conformation of the dbz unit appeared to be the least stable form. Interestingly, the reaction involving ZnMe2 did not lead to any alkylation product, whereas the employment of ZntBu2 resulted in full conversion of dbz to the O-alkylated product [tBuZn{PhC(O)C(OtBu)Ph}] already at -20-°C. A more complicated system was revealed for the reaction of dbz with ZnEt2. Treatment of a solution of dbz in toluene with one equivalent of ZnEt 2 at room temperature afforded a mixture of the O- and C-alkylated products [EtZn{PhC(O)C(OEt)Ph}] and [EtZn{OC(Ph)C(O)(Et)Ph}], respectively. The formation of the C-alkylated product was suppressed by decreasing the initial reaction temperature to -20-°C. Moreover, in the case of the dbz/ZnEt 2 system monitoring of the dbz conversion over the entire reaction course revealed a product inhibition effect, which highlights possible participation of multiple equilibria of different zinc alkoxide/ZnEt2 aggregates. Diffusion NMR studies indicated that dbz forms an adduct with the O-alkylated product, which is a competent species for executing the inhibition of the alkylation event. It all depends on R: The first systematic theoretical and experimental study of ZnR2 (R=Me, Et or tBu) with dibenzoyl revealed that the character of the metal-bonded alkyl group as well as the reaction conditions (e.g., ratio of the reagents, temperature) modulate the reaction outcome (see scheme). Monitoring the dibenzoyl conversion over the reaction course revealed a product-inhibition effect, which highlights possible participation of multiple equilibria of different zinc alkoxide/ZnR2 aggregates.
1,5,7-Triazabicyclo[4.4.0]dec-5-ene Enhances Activity of Peroxide Intermediates in Phosphine-Free α-Hydroxylation of Ketones
Wang, Yongtao,Lu, Rui,Yao, Jia,Li, Haoran
supporting information, p. 6631 - 6638 (2021/02/05)
The critical role of double hydrogen bonds was addressed for the aerobic α-hydroxylation of ketones catalyzed by 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), in the absence of either a metal catalyst or phosphine reductant. Experimental and theoretical investigations were performed to study the mechanism. In addition to initiating the reaction by proton abstraction, a more important role of TBD was revealed, that is, to enhance the oxidizing ability of peroxide intermediates, allowing DMSO to be used rather than commonly used phosphine reductants. Further characterizations with nuclear Overhauser effect spectroscopy (NOESY) confirmed the presence of double hydrogen bonds between TBD and the ketone, and kinetic studies suggested the attack of dioxygen on the TBD-enol adduct to be the rate-determining step. This work should encourage the application of TBD as a catalyst for oxidations.
Rearrangement of N- tert-Butanesulfinyl Enamines for Synthesis of Enantioenriched α-Hydroxy Ketone Derivatives
Li, Chun-Tian,Liu, Hui,Yao, Yun,Lu, Chong-Dao
, p. 8383 - 8388 (2019/10/14)
Treating chiral N-tert-butanesulfinyl ketimines with potassium hexamethyldisilazide (or potassium tert-butoxide) and methyl triflate gives N-methylated N-tert-butanesulfinyl enamine intermediates that undergo stereoselective [2,3]-rearrangement to afford α-sulfenyloxy ketones with excellent enantiopurities. This cascade of enamination-N-methylation-rearrangement was even used to generate acyclic tertiary α-hydroxy ketones bearing two α-substituents showing negligible differences in bulkiness, such as methyl and ethyl groups.
Phase-transfer-catalyzed enantioselective α-hydroxylation of acyclic and cyclic ketones with oxygen
Sim, Sui-Boon Derek,Wang, Min,Zhao, Yu
, p. 3609 - 3612 (2015/06/16)
An efficient and enantioselective α-hydroxylation of acyclic as well as cyclic ketones using molecular oxygen has been developed. This simple catalytic procedure uses a readily available phase-transfer catalyst and produces a wide range of valuable tertia
Highly efficient C-H hydroxylation of carbonyl compounds with oxygen under mild conditions
Liang, Yu-Feng,Jiao, Ning
supporting information, p. 548 - 552 (2014/01/23)
A transition-metal-free Cs2CO3-catalyzed α-hydroxylation of carbonyl compounds with O2 as the oxygen source is described. This reaction provides an efficient approach to tertiary α-hydroxycarbonyl compounds, which are highly valued chemicals and widely used in the chemical and pharmaceutical industry. The simple conditions and the use of molecular oxygen as both the oxidant and the oxygen source make this protocol very environmentally friendly and practical. This transformation is highly efficient and highly selective for tertiary C(sp3)-H bond cleavage. OH, so simple! A transition-metal-free Cs2CO 3-catalyzed α-hydroxylation of carbonyl compounds with O 2 provided a variety of tertiary α-hydroxycarbonyl compounds (see scheme; DMSO=dimethyl sulfoxide), which are widely used in the chemical and pharmaceutical industry. The simple conditions and the use of molecular oxygen as both the oxidant and the oxygen source make this protocol very efficient and practical.
A Mild Oxidizing Reagent for Alcohols and 1,2-Diols: o-Iodoxybenzoic Acid (IBX) in DMSO
Frigerio, Marco,Santagostino, Marco
, p. 8019 - 8022 (2007/10/02)
o-Iodoxybenzoic acid (IBX) smoothly oxidizes primary and secondary alcohols to aldehydes and ketones, respectively. 1,2-Diols are converted to α-ketols or α-diketones without any oxidative cleavage of the glycol C-C bond.IBX oxidations are easily conducted in DMSO solution at room temperature, with yields ranging from good to quantitative.
The Reaction of Benzil with Grignard Reagents
Holm, T.
, p. 278 - 284 (2007/10/02)
Benzil reacts with Grignard reagents forming, in the first step, the 1,2-addition product (C-alkylation), but often also the 1,4-addition product (O-alkylation) and the reduction product, benzoin.The product distribution has been determined for mechanistic purposes for 16 Grignard reagents using a standard procedure.These results, and observations made using deuteriated reagents and the 5-hexenyl radical probe indicate an electron transfer (ET) mechanism for reagents having hydrogen in the β-position, while a polar mechanism is the most efficient for methyl, phenyl, benzyl and allyl Grignard reagents in the ether solution.For the ET mechanism, a six-centre transition state is suggested.Furthermore, a distinction is made between the primary cage product (O-alkyl) resulting from immediate combination of the radical pair, and the secondary cage product (C-alkyl) formed in the cage after rearrangement. 5-Hexenylmagnesium bromide yields uncyclised primary and secondary cage product, but also significant amounts of cyclised C-alkylation product formed by escape of the radicals from the cage and re-encounter after cyclisation of 5-hexenyl to cyclopentylmethyl.A recently suggested mechanism based on the existence of stable radical ion pairs is found to be unacceptable.
On the Mechanism of the Thermal Conversion of Cyclopropenyl-Substituted Oxazolinones to Pyridines
Padwa, Albert,Cohen, Leslie A.,Gingrich, Henry L.
, p. 1065 - 1073 (2007/10/02)
Thermolysis or photolysis of a sample of a 3-cyclopropenyl-substituted 2H-azirine produced 2-methyl-3,4,5,6-tetraphenylpyridine in high yield.The reaction can best be rationalized by a mechanism involving formation of a nitrile ylide intermediate followed by intramolecular dipolar cycloaddition to give an azabenzvalene, which subsequently rearranges to the pyridine.The thermal chemistry of a series of cyclopropenyl-substituted oxazolinones was also investigated.These oxazolinones undergo a thermally induced 1,3-dipolar cycloreversion reaction with elimination ofcarbon dioxide to generate a nitrile ylide intermediate adjacent to the cyclopropene ring.This dipole can be trapped when the thermolysis of the oxazolinone was carried out in the presence of a reactive dipolarophile.Heating a sample of 2-phenyl-4-methyl-4-(1-methyl-2,3-diphenyl-2-cyclopropen-1-yl)-Δ2-oxazolin-5-one at 150 deg C for 24 h afforded a mixture of 2,3-dimethyltriphenylpyridine (45percent), 2,4-dimethyltriphenylpyridine (20percent), and 2,5-dimethyltriphenylpyridine (35percent).The formation of these products is proposed to involve a stepwise cycloaddition of the initially generated nitrile ylide to produce a bicyclobutyl zwitterion which can either collapse to give an azabenzvalene or undergo rearrangement to a cyclobutenyl cation. This latter species closes to produce two different aza Dewar benzenes.Reorganization of the azabenzvalene and aza Dewar benzenes gives rise to the observed pyridines.Alternate mechanisms based on a concerted intramolecular cycloaddition reaction of the nitrile ylide do not account for the observed product ratios.
