Spectrophotometric study of the formaldehyde-leuco-methylene blue reaction

The sensitivity of the reaction between foimaldchyde and Icuco-mcthyleno blue has been found to be increased in the presence of ethyl alcohol, acetone, dicthyl ketone and methyl ethyl ketone. Acetone has been found to be most effective. Sensitisers increase the absorption maximum and stabilise it, while the rate of development of methylene blue colour is slowed down.Sensitivity also depends upon the content of thiosulphate used to prepare the Icuco-base; a smaller amount of thiosulphate increases greater sensitivity.     

Novel fragmentation reaction of correolide

[reaction: see text] Pentacyclic triterpenoid natural product correolide (1) was converted to ketone 2 via ozonolysis. An unusual fragmentation reaction of ketone 2 with LiCl was discovered. This reaction is general among several similar substrates examined and appears to be specific for the correolide-type E-ring structure (ketone). A mechanism involving a retroaldol reaction, a nucleophilic opening of the epoxide, and a subsequent acetoxy elimination reaction was proposed.     

Copper‐Catalyzed Cross‐CouplingLigand‐Free Conditions Reaction of Thiols with Aryl Iodides under

Commercially available CuO powder is found to be a suitable catalyst for C‐S coupling reaction between aryl‐ and alkyl thiols and aryl iodides. Functional groups including halides, ketone, unprotected amine and heterocycles were tolerated by the reaction conditions employed.     

Domino reactions that combine an azido-Schmidt ring expansion with the Diels-Alder reaction

[reaction: see text] The combination of the intramolecular Schmidt reaction with the Diels-Alder reaction provides expedient access to a variety of heterocycles. Two different modes of reaction planning are presented. In one, the azide and ketone moieties necessary for the intramolecular Schmidt reaction originate on different molecules that are reacted and subsequently undergo a ring-adjustment step. Alternatively, an azido ketone can be used provided the ketone is deactivated by its presence in an enone.     

Catalytic enantioselective synthesis of alpha-aminooxy and alpha-hydroxy ketone using nitrosobenzene

The highly enantioselective and O-selective nitroso aldol reaction of tin enolates 2 and nitrosobenzene (1) has been developed with the use of (R)-BINAP-silver complexes as a catalyst. After the various silver salts were surveyed, the AgOTf and the AgClO4 complex were found to be optimal in the O-selective nitroso aldol reaction in both asymmetric induction (up to 97% ee) and regioselection (O/N = >99/1), affording aminooxy ketone 3. The product 3 can be transformed to alpha-hydroxy ketone 5 without any loss of enantioselectivity. Thus, the method provides an efficient approach to the catalytic enantioselective introduction of oxygen alpha- to the carbonyl group.     

Aluminum enolates via retroaldol reaction: catalytic tandem aldol-transfer—Tischtschenko reaction of aldehydes with aldol adducts of ketones to ketones

Bidentate aluminum chelates derived from biphenol, binaphthol and catechol were found to be efficient catalysts for aldol-transfer reactions of ketone to ketone aldol adducts with aliphatic or aromatic aldehydes giving rise to the formation of aldol adducts of ketones to the aldehydes. In the presence of an excess of an aliphatic aldehyde, a catalytic tandem aldol-transfer—Tischtschenko reaction is observed. The tandem reaction produces monoesters of 1,3-diols with high anti selectivity and with modest to good chemical yield. 1,2-Unsaturated aldehydes are less reactive in the aldol-transfer reaction and require 2-4 times higher load of the catalyst to be used than aliphatic and aromatic aldehydes. Poor diastereoselectivity was observed in the formation of α-substituted aldols and 2-substituted monoesters of anti-1,3-diols indicating that the aldol-transfer reaction is not diastereoselective with the catalysts studied. The utility of the highly 1,3-anti selective formation of diolmonoesters was found to be limited by acyl migration.     

An unexpected synthesis of an α,β,γ,δ-unsaturated ketone due to an abnormal opening of benzylidene acetal by bromide anion

An unexpected synthesis of an α, β, γ,δ-unsaturated ketone, which embodies a new type of oxy-carbon cyclic structure, was achieved, while we tried to construct the taxane CB-ring system. Also, a series of abnormal reaction phenomena was found to be related to the formation and reaction of seven membered cyclic benzylidene acetal.     

COMBINATORIAL SYNTHESIS OF MANNICH BASES IN SOLUTION／POLYMER REAGENT WORKUP

This paper describes a combinatorial synthesis the mannich bases in Solution through the Mannich reaction using 3 ketones,5 amines and formaldehyde in solution and hydrochloride as a catalyst and then using a macroporous quarterized ammonium resin(CO32-form)as a scavenge agent to remove the acid catalyst when the Mannich reaction is completed.It was found by GC/MS analysis that the symmetrical ketone,such as acetone,in the Mannich reaction mainly produces one Mannich base;while the asymmetrical ketone,such as 2-pentanone,gives two.     

Oligomerisation of phenyl acetylene over titanium oxide supported on silica - alumina catalyst

Titanium oxide on silica-alumina support is found to be effective for oligomerisation of phenyl acetylene. Cyclic trimerisation of the acetylene leading to trisubstituted benzene was also found to occur during the oligomerisation, in addition to the formation of small quantities of a ketone by the reaction of phenyl acetylene with moisture over the catalyst surface.     

Hydrogenation without a transition-metal catalyst: on the mechanism of the base-catalyzed hydrogenation of ketones

The hydrogenation of unsaturated organic substrates such as olefins and ketones is usually effected by homogeneous or heterogeneous transition-metal catalysts. On the other hand, a single case of a transition-metal-free and purely base-catalyzed hydrogenation of ketones was reported by Walling and Bollyky some 40 years ago. Unfortunately, the harsh reaction conditions (ca. 200 degrees C, >100 bar H(2), potassium tert-butoxide as base) limit the substrate spectrum of this reaction to robust, nonenolizable ketones such as benzophenone. We herein present a mechanistic study of this process as a basis for future rational improvement. The base-catalyzed hydrogenation of ketones was found to be irreversible, and it shows first-order kinetics with respect to the substrate ketone, hydrogen, and catalytic base. The rate of the reaction depends on the type of alkali ion present (Cs > Rb - K > Na > Li). Using D(2) instead of H(2) revealed a rapid base-catalyzed isotope exchange/equilibration between the gas phase and the solvent as a concomitant reaction. The degree of deuteration of the product alcohols did not indicate a significant kinetic isotope effect. It is proposed that both ketone reduction and isotope exchange proceed via similar six-membered cyclic transition states involving the H(2)(D(2))-molecule, the alkoxide base, and the ketone (solvent alcohol in the case of isotope exchange). Mechanistic analogies are pointed out which apparently exist between the base-catalyzed hydrogenation of ketones studied here and the Ru-catalyzed asymmetric ketone hydrogenation developed by Noyori. In both cases, heterolysis of the hydrogen molecule appears to be assisted by a Br?nsted-base (i.e., alkoxide), the latter being bound to the substrate ketone or the catalyst ligand, respectively, by a bridging Lewis-acidic alkali ion.     

Modified Julia fluoroolefination: selective preparation of fluoroalkenoates

The modified Julia olefination reaction has been applied to develop a stereoselective synthesis of fluoroalkenoate derivatives from a fluorobenzothiazolyl sulfone and aldehydes or a ketone. The olefination reaction can be achieved by using a variety of bases. DBU and DBU in the presence of MgBr2 were found to be the most efficient systems to prepare either (Z)- or (E)-alkenoates in moderate to excellent stereoselectivity.     

An extremely efficient three-component reaction of aldehydes/ketones, amines, and phosphites (Kabachnik-Fields reaction) for the synthesis of alpha-aminophosphonates catalyzed by magnesium perchlorate

Commercially available magnesium perchlorate is reported as an extremely efficient catalyst for the synthesis of alpha-aminophosphonates. A three-component reaction (3-CR) of an amine, an aldehyde or a ketone, and a di-/trialkyl phosphite (Kabachnik-Fields reaction) took place in one pot under solvent-free conditions to afford the corresponding alpha-aminophosphonates in high yields and short times. The use of solvent retards the rate of the reaction and requires a much longer reaction time than that for neat conditions. The reactions involving an aldehyde, an aromatic amine without any electron-withdrawing substituent, and a phosphite are carried out at rt. The reactions involving cyclic ketones, aromatic amines with an electron-withdrawing substituent, and aryl alkyl ketone (e.g., acetophenone) require longer reaction times at rt or heating. Magnesium perchlorate was found to be superior to other metal perchlorates and metal triflates during the reaction of 4-methoxybenzaldehyde, 2,4-dinitroaniline, and dimethyl phosphite. The catalytic activity of various magnesium compounds was influenced by the counteranion, and magnesium perchlorate was found to be the most effective. The reaction was found to be general with di-/trialkyl phosphites and diaryl phosphite. The Mg(ClO4)2-catalyzed alpha-aminophosphonate synthesis in the present study perhaps represents a true three-component reaction as no intermediate formation of either an imine or alpha-hydroxy phosphonate was observed that indicated the simultaneous involvement of the carbonyl compound, the amine, and the phosphite in the transition state.     

Convergent Approaches to Saudin Intermediates

Different convergent approaches to the highly oxygenated sesquiterpene natural product saudin ( 1 ), has been investigated. Our strategy has included a Michael addition and aldol condensation reaction as key steps. During the synthetic development, we have found serious steric hindrance when an α‐Me‐substituted alkyl vinyl ketone was used. Such steric hindrance has been overcome by synthesizing the vinyl ketone 16 through an anionic fragmentation, which was carefully studied. Finally, the intermediate 18 has been synthesized in a one‐pot reaction from the vinyl ketone 16 and has been cyclized to obtain the promising tricyclic intermediate 20 .     

CC Coupling of Ketones with Methanol Catalyzed by a N‐Heterocyclic Carbene–Phosphine Iridium Complex

An N‐heterocyclic carbene–phosphine iridium complex system was found to be a very efficient catalyst for the methylation of ketone via a hydrogen transfer reaction. Mild conditions together with low catalyst loading (1 mol %) were used for a tandem process which involves the dehydrogenation of methanol, C?C bond formation with a ketone, and hydrogenation of the new generated double bond by iridium hydride to give the alkylated product. Using this iridium catalyst system, a number of branched ketones were synthesized with good to excellent conversions and yields.     

Direct synthesis of Cbz-protected β-amino ketones by iodine-catalyzed three-component condensation of aldehydes, ketones and benzyl carbamate

Iodine has been found to be very effective catalyst for a Mannich reaction between an aryl aldehyde, an aryl ketone and benzyl carbamate, even though this is a less reactive amine, to produce Cbz-protected β-aryl β-amino carbonyl compounds in high yields.     

A facile and catalytic method for selective deprotection of tert-butyldimethylsilyl ethers with copper(II) bromide

Copper(II) bromide is found to be a simple and efficient catalyst for selective deprotection of tert-butyldimethylsilyl ethers of alcohols/phenols at ambient temperature. Various labile functional groups such as ketal, alkene, ketone, OTBDPS, OTHP and allyl and benzyl ethers are found to be compatible under the reaction conditions.     

苯甲酮不对称还原反应的理论研究

本文用AM1分子轨道方法研究了1,3,2-噁唑硼烷对苯甲酮的不对称催化还原.反应经历了噁唑硼烷-硼烷配合物的形成及其与苯甲酮的结合、氢转移及脱去噁唑硼烷形成手性产物二级醇-硼烷配合物四步过程.获得了各步的反应热、速度控制步骤的过渡态结构和位能曲线及其相应的反应活化能,计算发现反应机理中的第3步氢转移产物有四员环结构特征.     

Well-defined,air-stable (NHC)Pd(Allyl)Cl (NHC = N-heterocyclic carbene) catalysts for the arylation of ketones

A number of palladium-N-heterocyclic carbene (NHC) complexes were found to be active catalysts for the arylation of ketones. A large number of substrates, both aryl halides and ketones, are compatible with the reaction conditions. The ketone arylation reactions are achieved with low catalyst loading in short reaction times using aryl chlorides and triflates as reactive partners. [reaction: see text]     

To the core of autocatalysis in cyclohexane autoxidation

Despite their industrial importance, the detailed reaction mechanism of autoxidation reactions is still insufficiently known. In this work, complementary experimental and theoretical techniques are employed to address the radical-chain initiation in the autoxidation of cyclohexane with a particular focus on the "lighting-off" of the oxidation by (added) cyclohexanone. We used a newly developed method to quantify the intrinsic rate of chain initiation as well as the rate enhancement by cyclohexanone and several other (oxygenated) molecules. On the basis of first principles, the hitherto assumed perhemiketale mechanism was found to be many orders of magnitude too slow to account for the observed initiation enhancement by the ketone. Instead, it is shown that the pronounced chain-initiation enhancement by the ketone is attributable to a newly proposed concerted reaction between cyclohexyl hydroperoxide and cyclohexanone, in which the (.)OH radical breaking away from the hydroperoxide abstracts an alphaH atom from the ketone, thereby energetically assisting in the cleavage of the RO--OH bond. This reaction is highly efficient in generating radicals as it quasi-excludes geminate in-cage recombination. As a result, the ketone oxidation product at a level of 1 mol % increases the initiation rate by one order of magnitude, and so acts as a highly efficient "autocatalyst" in autoxidation reactions. An analogous reaction with cyclohexanol, although estimated to be even faster, has only a marginal effect on the overall kinetics, owing to the fast subsequent formation of HO(2) (.) radicals that very rapidly terminate with other ROO(.) radicals. Finally, solid evidence is presented that, also in absence of oxygenates, ROOH initiation is actually a bimolecular reaction, involving concerted H abstraction from the alkane substrate by the nascent (.)OH.     

The polymerization of acrylates using a combination of a carbonyl compound and an amine as a photo-initiator system

Photo-initiator systems for the polymerization of acrylates, based on a mixture of an aryl ketone and an α,ω-diaminoalkane, have been investigated. Rate constants for the photoreduction of fluorenone by α,ω-diaminoalkanes have been evaluated: it was found that CH₃N groups are more relative than CH₃CH₂N groups. The relative rates of photo-oxidation of α,ω-diaminalkanes sensitised by benzophenone have been determined. Surprisingly, little correlation exists between the susceptibility of an amine towards oxidation and its ability to reduce excited carbonyl groups. Several mixtures composed of an aryl ketone and an α,ω-diaminoalkane were found to initiate the polymerization of methyl methacrylate. The efficiency of initiation appears to be related to the efficiency of reaction of the triplet carbonyl compound with the amine. The efficiency of a particular combination of an aryl ketone and an amine to cure films of acrylate oligomers is also governed to some extent by the efficiency of reaction of the triplet carbonyl compound with the amine. However, the structure of the amino alkyl radical produced in the initiation reaction appears to be of greater importance in determining the efficiency of polymerization. Radicals of the type R₂N?HCH₂OR were found to be highly efficient.