Direct Observation of Unstable Reaction Intermediates by Acid‐Base Complex Formation

The structures of several unstable or metastable reaction intermediates that were photoproduced in crystals were analyzed by using X‐ray techniques. The presence of enough void space around the reactive group(s) is an essential factor for the reaction to occur with retention of the single‐crystal form. To expand the void space, an acid group (COOH) was substituted onto the reactant molecule and acid‐base complex crystals were prepared with several amines, such as dibenzylamine and dicyclohexylamine. Following the formation of such acid‐base complexes in crystals, the metastable structures of nitrenes and red species of photochromic salicylideneanilines have been successfully analyzed by using X‐ray techniques. Moreover, the structure of a Pt complex anion in the excited state has been analyzed, which formed acid‐base complex crystals with various alkylammonium cations. The formation of acid‐base complexes will be a powerful tool for directly observing the structure of unstable or metastable reaction intermediates by using X‐ray techniques.     

Enantiopure α-imino glyoxylate: a versatile substrate for the spontaneous asymmetric synthesis of unnatural hydroxyaryl glycinates

A novel synthesis of useful enantiomerically pure arylglycinates via spontaneous reaction between phenol or naphthol derivatives and enantiopure α-imino glyoxylate in the absence of an acid catalyst is reported. A library of enantiopure substituted phenol or naphthol glycinates was obtained in good yields and high diastereoselectivities. Diastereoisomerically pure aryl glycinates were obtained by direct flash chromatography separation of the crude reaction mixture. The free OH moiety of the phenols or naphthols contributed to the activation of the imino group to form an intermolecular hydrogen bond and promoted the reaction in the absence of an acid catalyst, as shown in the transition state reported. The diastereoselectivity is due to thermodynamic control in the addition step.     

Etude de l'acylation de l'acétyl-3 acétoxy-8 indolizine par action de chlorures d'acide en présence de chlorure d'aluminium

Study of acylation of 3-acetyl-8-acetoxyindolizine by miscellaneous acid chlorides in the presence of aluminium chloride shows that this reaction is either limited to a transesterification (in the case of benzoyl chloride) or leads to introduction of an acyl group in position 1 with simultaneous liberation of the phenol function in position 8. When acylation takes place, acetyl chloride resulting from the cleavage of the acetoxy group competes with the acid chloride used in the reaction. Predominant acylation by the latter is observed when the reaction is performed with ethoxalyl chloride or with non branched aliphatic acid chlorides; by contrast solely acetylation takes place when pivaloyl or phenylacetyl chloride is used. These results are tentatively explained by a process related to the Fries rearrangement. The hypothesis of intramolecular transfer of an acyl group from the ester function in position 8 can be discarded by the observed results.     

Synthesis of Pyrrolidine Derivatives by a Platinum/Brønsted Acid Relay Catalytic Cascade Reaction

A new catalytic reaction for the synthesis of pyrrolidine derivatives is presented. The method implies the coupling of N‐Boc‐protected alkynamine derivatives and appropriate alkenes or alkynes in a process catalysed by a platinum/triflic acid catalytic binary system. This reaction is believed to proceed through a cascade process implying an initial platinum‐catalysed cycloisomerization of the alkynamine derivative followed by a triflic acid promoted nucleophilic addition of the alkene or alkyne and trapping of the cationic species formed by the Boc group. Not only simple alkenes and alkynes were used in this reaction but also allyltrimethylsilane and propargyltrimethylsilane. Particularly, when allyltrimethylsilane is used as the alkene counterpart interesting bicyclic compounds containing a trimethylsilane group are obtained. However, when propargyltrimethylsilane is used in the presence of water we observed the formation of a related bicyclic compound lacking the trimethylsilane group and containing an exocyclic carbon?carbon bond.     

One-pot two-step reaction of selenosulfonate with isocyanides and allyl alcohol under aqueous conditions:Atom-economic synthesis of selenocarbamates and allyl sulfones

In many reactions involving selenosulfonate or thiosulfonate,the sutfone group often leaves in form of benzenesutfinic acid or sodium benzenesulfinate.A one-pot two-step reaction of selenosulfonate with isocyanides and allyl alcohol under aqueous conditions to afford selenocarbamates and allyl sulfone compounds is reported.The sulfinic acid as the first-step side product is converted to the allyl sulfone compound by water promoted reaction with allyl alcohol.Water acts as both an oxygen source of selenocarbamates and as a promoter to drive the second step reactio n.The reactions have the advantages of mild conditions,green,environment-friendly,and high atomic economy.     

Palladium and carbon synergistically catalyzed room-temperature hydrodeoxygenation(HDO) of vanillyl alcohol–A typical lignin model molecule

Vanillyl alcohol,which is made up of an aromatic ring,an alcoholic hydroxyl group,a phenolic hydroxyl group and a methoxy group,was selected as the model molecule of lignin.Various carbon materials supported Pd catalysts were chosen to catalyze the HDO of vanillyl alcohol.The catalysts were characterized via TEM,TPD,XRD,XPS and CO-chemisorption.It was found that different carbon materials could obviously influence the particle sizes,dispersion and distribution of Pd or Pd O particles.Palladium and carbon can synergistically catalyze the room-temperature HDO of vanillyl alcohol even at room temperature,and the carboxyl group was found to be the effective active acid site during the reaction.Possible reaction mechanism was also proposed.The existence of the effective active acid sites on the carbon supports could obviously lower the reaction temperature without decreasing the selectivity,as a result,making the production of renewable fuels by HDO much more economically feasible,which is of much importance.     

Highly Stereoselective Cationic Cyclization Assisted by a Sulfenyl Group. Scope, Limitation, and Mechanism

When 8-acetoxy-2-methyl-9-(phenylthio)-2-nonene (1a) was treated with an acid, followed by a base, alkylative cyclization proceeded to give a mixture of 1,2-disubstituted cyclohexanes: 2a, 3a, and 4a. The stereochemistry of the reaction was only slightly affected by the leaving group and the reaction conditions, such as the temperature, solvent, and acid. However, the bulkiness of the sulfenyl group had a great effect on the stereochemical course of the reaction. High trans selectivity was attained when 1c (a derivative of 1a with a bulkier sulfenyl group) was used as a substrate. On the other hand, the length and rigidity of the carbon chain of the substrate also had a major effect on the stereochemistry of the reaction; a high cis selectivity was observed when 10a (a one-carbon-fewer analog of 1a) or 15a (a derivative with one more double bond in the carbon chain than in 1a) was used as the substrate. The reaction proceeded via a 6,5- or 5,5-fused-ring intermediate. The sulfenyl-group-assisted reaction could be a useful method for the stereoselective cyclization of acetates of alpha-sulfenylated secondary alcohols.     

Pd-Catalyzed Synthesis of Vinyl Arenes from Aryl Halides and Acrylic Acid

Acrylic acid is presented as an inexpensive, non-volatile vinylating agent in a palladium-catalyzed decarboxylative vinylation of aryl halides. The reaction proceeds through a Heck reaction of acrylic acid, immediately followed by protodecarboxylation of the cinnamic acid intermediate. The use of the carboxylate group as a deciduous directing group ensures high selectivity for monoarylated products. The vinylation process is generally applicable to diversely substituted substrates. Its utility is shown by the synthesis of drug-like molecules and the gram-scale preparation of key intermediates in drug synthesis.     

多聚磷酸存在下取代6-苄硫基嘧啶与羧酸的环合反应研究

以多聚磷酸(PPA)为催化剂, 对取代6-苄硫基嘧啶与羧酸的反应进行了研究. 当羧酸为脂肪酸时, 在60-80 ℃下反应, 可选择性地得到6-苄硫基嘌呤衍生物; 改用芳香酸时, 则得到硫上的苄基被脱除的6-巯基嘌呤和嘧啶并[5,4-d]噻唑; 如果将嘧啶4-位上伯胺取代基变成仲胺取代基, 只得到嘧啶并[5,4-d]噻唑. 通过双途径反应机理对上述现象进行了解释.     

Synthesis of organofunctionalized polysiloxane from polymeric tributylstannyl ester of silicic acid and chlorosilanes

Polymeric tributylstannyl ester of silicic acid (PTBS) was demonstrated to be an effective material for the preparation of functionalized polysiloxane derivatives (2). The reaction of PTBS and monochlorosilane (1), which possessed an organofunctional group such as the acetoxy or methylmethacrylate group, proceeded readily at room temperature under neutral conditions to give 2 with the elimination of the tributyltin group. The molecular weight of 2 estimated by GPC measurement was almost the same as that of starting PTBS. Such metal-exchange reaction was applicable for the incorporation of two kinds of silyl units into polysiloxane 2 by employing these monochlorosilanes 1 at the same time in the reaction. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2363–2369, 1999     

Intramolecular transacylation: fragmentation of protonated molecules via ion‐neutral complexes in mass spectrometry

An intramolecular transacylation reaction was observed in the mass spectrometry of molecules containing both benzoyl and carboxymethyl groups on an aromatic heterocyclic core. The reaction is triggered by a dissociative protonation on the heterocyclic ring at the atom (carbon or nitrogen) that bonds to the benzoyl group, leading to an intermediate ion‐neutral complex. The incipient benzoyl cation in the complex migrates to attack the carboxyl group of the neutral partner at the carbonyl or hydroxyl oxygen under thermodynamic or kinetic control, respectively. Elimination of benzoic acid followed by loss of carbon monoxide takes place as a result of the transacylation. Copyright © 2009 John Wiley & Sons, Ltd.     

Rhodium-catalyzed annulation reactions of 2-cyanophenylboronic acid with alkynes and strained alkenes

[reaction: see text]. A new [3 + 2] annulation reaction was developed in which 2-cyanophenylboronic acid reacted as a three-carbon component with alkynes or alkenes to afford substituted indenones or indanones. The use of an alkynoate even produced benzotropone, a formal [3 + 2 + 2] adduct. The cyclic skeletons were constructed by intramolecular nucleophilic addition of an intermediate organorhodium(I) species to a cyano group.     

An efficient,regio- and stereoselective palladium-catalyzed route to tetrasubstituted olefins

An efficient, regio- and stereoselective palladium-catalyzed route to tetrasubstituted olefins has been developed, which involves the intermolecular coupling of an aryl iodide, an internal alkyne, and an arylboronic acid. The reaction involves cis-addition of the aryl group from the aryl halide to the less hindered or less electron-poor end of the alkyne, while the aryl group from the arylboronic acid adds to the other end. [reaction: see text]     

QUALITATIVE UNTERSUCHUNGEN ZUR PHOTOLYSE EINFACHER DIPEPTIDE

Abstract— The photolyses of eight chromatographical pure dipeptides were studied. They were irradiated by the total spectrum of a high pressure mercury lamp. The resulting products were separated by electrophoresis and identified by paper chromatography. It was found that the carbonyl group of the N-terminal amino acid was eliminated in a dipeptide; an amine and an amino acid were found as primary products. This reaction is accompanied by a second reaction, the decarboxylation of the C-terminal amino acid. Possible mechanisms of these reactions are discussed.     

Mechanism and kinetics of the polymerization of thermoplastic polyimides. I. Study of the pyromellitic anhydride/aromatic amine system

We have synthesized model compounds representing the repeating units of a polyamic acid prepared from pyromellitic anhydride and an aromatic amine. They were characterized with HPLC, ¹H and ¹³C liquid and solid NMR and FTIR. The Kinetic study of the ring dehydration reaction of model compounds showed that the reaction paths were very different, depending on the experimental conditions (isotherms, liquid, or solid states). They could lead to a deterioration of the polyamic of the polyamic acid by the formation of side reactions. These reactions could predominate as a result of the existence of an equilibrium between the amic acid group and starting monomers.     

用微电极上的光谱电化学法测定催化反应的速率常数

首次采用微电极上的光谱电化学法测定了K_4Fe(CN)_6-抗坏血酸、K_4Fe(CN)_6-组氨酸体系的催化反应速率常数。实验发现, 当抗坏血酸或组氨酸的浓度同K_4Fe(CN)_6的浓度相当甚至稍低时, 仍可按准一级化学反应来处理, 并提出了合理的解释。     

Polymerization of bis(2-oxazoline) compounds with dicarboxylic acids

A side reaction was found in the reaction of a 2-oxazoline compound with a carboxylic acid. It is an oxazoline ring opening addition to an amide group formed by the main reaction. In addition, certain phosphites were found to act as catalyst for the side reaction. The rate constants of the main and side reactions in the system of 2-phenyl-2-oxazoline and n-octanoic acid were obtained through simulation of the reactions on an analog computer. The side reaction makes it impossible for a very high molecular weight polymer to form in the reaction of a bis-2-oxazoline with a dicarboxylic acid, but makes it possible for a new crosslinked polymer to form when excess bis-2-oxazoline and a dicarboxylic acid are heated in the presence of a certain phosphite.     

Adsorptive voltammetry and hydrolysis kinetics of loprazolam mesilate

Loprazolam is determined by square-wave adsorptive stripping voltammetry in 0.04M ammonium chloride at pH 4.0, with an accumulation potential of -0.25 V vs. Ag/AgCl/KCl(s), at which the nitro group is reduced to a hydroxylamine group, with adsorption of the product. Cathodic stripping results in reduction of the azomethine bond of the adsorbed product. With a deposition time of 120 sec the detection limit is 2.5 x 10(-10)M. The relative standard deviation is 1.7% for 5 x 10(-8)M loprazolam (60 sec deposition). Reversible hydrolysis of the azomethine group occurs in sulfuric or hydrochloric acid. The reaction is initially first-order, followed by an apparent second-order reaction. First-order rate constants and half-lives are reported for 0.1-1M sulfuric acid and 0.02M hydrochloric acid media and compared with the values for nitrazepam hydrolysis.     

α,α-Dialkylglycines obtained by solid phase Ugi reaction performed over isocyanide functionalized resins

The multicomponent Ugi reaction is a straightforward method that can be used for the synthesis of highly hindered C-tetrasubstituted amino acids by reacting an amine, a ketone or aldehyde, a carboxylic acid and an isocyanide. In the present work, the synthesis of several α,α-dialkylglycines (α,α-diethylglycine, Deg; α,α-dipropylglycine, Dpg; 1-amino-1-cyclohexanecarboxylic acid, Ac₆c) was achieved by solid phase Ugi reaction using resins functionalized with the isocyanide group. Since no resins with these features were available commercially, the functionalization of an aminomethylated resin started by the use of glycine (Gly), β-alanine (β-Ala) and γ-aminobutyric acid (GABA) as spacers. After spacer N-formylation, followed by dehydration, isocyanide functionalised resins were obtained. The resins were then used in solid phase Ugi reaction, using phenylacetic acid as the acid component, 4-methoxybenzylamine as the amine component and different ketones, to afford the desired N-acylated α,α-dialkylglycines in good overall yields (60–80%), after acidolytic cleavage from the resin, thus proving the feasibility of this approach.     

Acylation of hydrazides with acetic acid and formic acid

In peptide synthesis, hydrazides are important intermediates for the azide coupling method. A hydrazide is converted to the corresponding azide in the presence of an acid and a nitrite. When acetic acid (or formic acid) is used as the acid, partial acetylation (or formylation) of the hydrazide occurs as a side reaction. Formylation of the hydrazide is much faster than acetylation. Removal of the formyl group on the hydrazide with hydrazine and hydroxylamine was studied. The rate of deformylation with hydrazine treatment is faster than that with hydroxylamine treatment.