Bioinspired Intramolecular Diels–Alder Reaction: A Rapid Access to the Highly‐Strained Cyclopropane‐Fused Polycyclic Skeleton

A bioinsipred gold‐catalyzed tandem Diels–Alder/Diels–Alder reaction of an enynal and a 1,3‐diene, forming the highly‐strained benzotricyclo[3.2.1.0^2,7]octane skeleton, was reported. In contrast, a Diels–Alder/Friedel–Crafts tandem reaction occurred instead when silver salts were used as the catalyst. Although both reactions experienced the similar Diels–Alder reaction of a pyrylium intermediate with a 1,3‐diene, they have different reaction mechanisms. The former proceeded with a stepwise Diels–Alder reaction, while the latter one with a concerted one.     

Fünf- und sechsgliedrige cyclische Phosphonsäure-diamide und-thioester-amide sowie Spirobi[oxazaphosphole]

Five- and Six-Membered Cyclic Phosphonic Diamides, Thioester-amides and Spirobi[oxazaphospholes] By reaction of the 1,2-diaminobenzene derivatives 1a–d with the phosphonoyl dichlorides 2a–g , the 1,3-dihydro-1,3,2-benzodiazaphosphol-2-ones 4a–q are obtained. The phosponoyl dichlorides 2a–e, 2g , and 2h yield with naphthalene-1,8-diamines ( 5 ) the diazaphosphinones 6a–g under similar reaction conditions. The thiazaphosphole oxides 9a–d are accessible by reaction of the phosphonoyl dichlorides 2a–d with 2-aminobenzenethiol ( 7 ). Unexpectedly, the reaction of the dichlorides 2a and 2b with 2-aminophenol ( 10 ) led to the spirobi[oxazaphospholes] 13a and 13b , respectively.     

High‐Yielding Synthesis of the Anti‐Influenza Neuraminidase Inhibitor (−)‐Oseltamivir by Two “One‐Pot” Sequences

The efficient asymmetric total synthesis of (?)‐oseltamivir, an antiviral reagent, has been accomplished by using two “one‐pot” reaction sequences, with excellent overall yield (60 %) and only one required purification by column chromatography. The first one‐pot reaction sequence consists of a diphenylprolinol silyl ether mediated asymmetric Michael reaction, a domino Michael reaction/Horner–Wadsworth–Emmons reaction combined with retro‐aldol/Horner–Wadsworth–Emmons reaction and retro Michael reactions, a thiol Michael reaction, and a base‐catalyzed isomerization. Six reactions can be successfully conducted in the second one‐pot reaction sequence; these are deprotection of a tert‐butyl ester and its conversion into an acyl chloride then an acyl azide, Curtius rearrangement, amide formation, reduction of a nitro group into an amine, and a retro Michael reaction of a thiol moiety. A column‐free synthesis of (?)‐oseltamivir has also been established.     

An unusual substitution reaction of an aromatic sulfonic group based on 3-carbonyl-4-phenolsulfonic acid

An unusual substitution reaction of an aromatic sulfonic group based on 3-carbonyl-4-phenolsulfonic acid was discovered in a diazo-coupling process.The reaction occurred under mild reaction conditions (pH 8.0-9.0.0-5 C,solvent:water) within a short reaction time(1h).A plausible substitution reaction mechanism by phenol-ketone resonance was proposed.     

Efficient One-Pot Synthesis of 2-Carbonyl- 1-indanols by Palladium-Catalyzed Tandem Heck–Aldol Reaction

2-Carbonyl-1-indanols were synthesized in moderate to good yields by the reaction of orthohalogenated aryl aldehyde with Morita–Baylis–Hillman adducts via a one-pot, palladium-catalyzed tandem Heck–aldol reaction. Various Morita–Baylis–Hillman adducts were examined to find the scope and limitations of this process.     

A DFT Study on the Reaction Pathways for Carbon?Carbon Bond‐Forming Reactions between Propargylic Alcohols and Alkenes or Ketones Catalyzed by Thiolate‐Bridged Diruthenium Complexes

The reaction pathways of two types of the carbon? carbon bond‐forming reactions catalyzed by thiolate‐bridged diruthenium complexes have been investigated by density‐functional‐theory calculations. It is clarified that both carbon? carbon bond‐forming reactions proceed through a ruthenium–allenylidene complex as a common reactive intermediate. The attack of π electrons on propene or the vinyl alcohol on the ruthenium–allenylidene complex is the first step of the reaction pathways. The reaction pathways are different after the attack of nucleophiles on the ruthenium–alkynyl complex. In the reaction with propene, the carbon? carbon bond‐forming reaction proceeds through a stepwise process, whereas in the reaction with vinyl alcohol, it proceeds through a concerted process. The interactions between the ruthenium–allenylidene complex and propene or vinyl alcohol have been investigated by applying a simple way of looking at orbital interactions.     

The behavior of 2‐substituted‐1,3‐diphenylpropane‐1,3‐tione toward organophosphorus reagents

The reaction of 2‐benzylidene‐1,3‐diphenylpropanetrione ( 1a ) with phosphorus ylides 2a–c afforded the new phosphonium ylides 4a–c . Trialkyl phosphites 3a–c react with 1a to give the respective dialkyl phosphonate products 5a–c . On the other hand, the olefinic compounds 6 and 7 were isolated from the reaction of 1b with Wittig reagents 2 . Moreover, trialkyl phosphites reacted with 1b to give products 8a–c . Possible reaction mechanisms are considered, and the structural assignments are based on analytical and spectroscopic evidence. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:57–64, 2000     

N-Heterocyclic carbenes as ligands in palladium-catalyzed Tsuji–Trost allylic substitution

A Pd(0)-catalyzed allylic substitution (i.e., Tsuji–Trost reaction) using N-heterocyclic carbene as a ligand was investigated. It has been proven that an imidazolium salt 2d having bulky aromatic rings attached to the nitrogens in its imidazol-2-ylidene skeleton is suitable as a ligand precursor and that a Pd₂dba₃–imidazolium salt 2d–Cs₂CO₃ system is highly efficient for producing a Pd–NHC catalyst in this reaction. Allylic substitution using a Pd–NHC complex differed from that using a Pd–phosphine complex as follows: (1) the reaction using a Pd–NHC complex required elevated temperature (50 °C or reflux in THF), (2) allylic carbonates were inert to a Pd–NHC complex, and (3) nitrogen nucleophiles such as sulfonamide and amine did not react with allylic acetate. It was also found that allylic substitution with a soft nucleophile using a Pd–NHC catalyst proceeds via overall retention of configuration to give the product in a stereospecific manner, the stereochemical reaction course obviously being the same as that of the reaction using a Pd–phosphine complex.     

Advances in the Bestmann–Ohira Reagent–Assisted Regioselective Synthesis of Substituted Pyrazoles,Triazoles, and Oxazoles

The Bestmann–Ohira reagent serves as a versatile platform for the regioselective construction of pyrazoles, triazoles, and oxazoles via a cycloaddition reaction and multicomponent reaction. In this review, we have summarized the most significant advances in the Bestmann–Ohira reagent (BOR)–assisted construction of functionalized five–membered heterocycles reported in the literature up to 2012.     

l-proline and l-histidine co-catalyzed Baylis–Hillman reaction

Baylis–Hillman reaction between an aldehyde and an activated alkene, such as alkyl vinyl ketones, acrylates, acrylonitrile, and vinylsulfones, giving the β-hydroxy-α-methylene carbonyl compounds, is a versatile and atom-economical carbon–carbon bond-forming reaction. This reaction usually is catalyzed by strong Lewis bases such as tertiary amines and suffers from slow reaction rate. In this paper the Baylis–Hillman reaction between arylaldehydes and methyl vinyl ketone was successfully realized by a catalytic amount of l-proline and l-histidine system to give the corresponding normal Baylis–Hillman adducts in moderate to high yields for the first time. The effects of solvent and reagent electro property on the yields of this reaction were also investigated. Proline and histidine are naturally widely present amino acids in food system; furthermore, aldehydes and activated alkenes can also be easily produced in food processing, so proline and histidine co-catalyzed Baylis–Hillman reaction may find application in explaining some phenomena in food processing.     

Umpolung Reactions of α‐Imino Esters: Useful Methods for the Preparation of α‐Amino Acid Frameworks

This paper summarizes our recent efforts toward the development of tandem reactions utilizing umpolung reactions of α‐imino esters. A highly diastereoselective tandem N‐alkylation–Mannich reaction of α‐imino esters was developed. A tandem N‐alkylation–addition reaction of α‐imino esters derived from ethyl glyoxylate with various aldehydes proceeded to give 1,2‐amino alcohols. The same reaction also proceeded efficiently using a novel flow system comprising two connected microreactors. Novel syntheses of α‐quaternary alkynyl amino esters and allenoates were developed through the use of umpolung N‐addition to β,γ‐alkynyl α‐imino esters, followed by regioselective acylation. In addition, a highly regioselective tandem N‐alkylation–vinylogous aldol reaction of β,γ‐alkenyl α‐imino esters was discovered. N‐Alkylation of α‐iminophosphonates followed by a Horner–Wadsworth–Emmons reaction with aldehydes occurred to afford enamines, which can be used in a four‐component coupling reaction with methyl vinyl ketone. α‐N‐Acyloxyimino esters served as highly efficient substrates for the N,N,C‐trialkylation reaction to introduce various nucleophiles at the imino nitrogen and carbon atoms.     

Study of the oxidation of some catechols in the presence of 4‐amino‐3‐thio‐1,2,4‐triazole by digital simulation of cyclic voltammograms

Electrochemical oxidation of catechol and its derivatives ( 1a–d ) has been studied in the presence of 4‐amino‐3‐thio‐1,2,4‐triazole ( 3 ) at various pHs. Some electrochemical techniques such as cyclic voltammetry using the diagnostic criteria derived by Nicholson and Shain for various electrode mechanisms and controlled‐potential coulometry were used. Results indicate the participation of catechols ( 1a–d ) with 3 in an intramolecular cyclization reaction to form the corresponding 1,2,4‐triazino[5,4‐b]‐1,3,4‐thiadiazine derivatives. In various scan rates, based on an electron transfer–chemical reaction–electron transfer–chemical reaction mechanism, the observed homogeneous rate constants (k_obs) for Michael addition reaction were estimated by comparing the experimental cyclic voltammetric responses with the digital simulated results. The oxidation reaction mechanism of catechols ( 1a–d ) in the presence of 4‐amino‐3‐thio‐1,2,4‐triazole ( 3 ) was also studied. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 340–345, 2007     

The use of tetraalkylphosphonium–tetrafluoroborate–tetrafluoroboric acid in the curing of a liquid crystalline epoxy resin

Tetraalkylphosphonium–Tetrafluoroborate–Tetrafluoroboric Acid was used as a catalyst in the curing of a liquid crystalline epoxy. Under some conditions the Tetraalkylphosphonium–Tetrafluoroborate–Tetrafluoroboric Acid actually retarded the reaction. An extensive experimental and kinetic analysis is presented anda mechanism for the reaction retardation is proposed. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1457–1471, 1998     

Aryl–Phenyl Scrambling in Intermediate Organopalladium Complexes: A Gas‐Phase Study of the Mizoroki–Heck Reaction

The intramolecular aryl–phenyl scrambling reaction within palladium–DPPP–aryl complex (DPPP=1,3‐bis(diphenylphosphino)propane) ions was analyzed by state‐of‐the‐art tandem MS, including gas‐phase ion/molecule reactions. The Mizoroki–Heck cross‐coupling reaction was performed in the gas phase, and the intrinsic reactivity of important intermediates could be examined. Moreover, linear free‐energy correlations were applied, and a mechanism for the scrambling reaction proceeding via phosphonium cations was assumed.     

Iron-catalyzed annulation reaction of arylindium reagents and alkynes to produce substituted naphthalenes

We report here an iron–bisphosphine complex-catalyzed annulation reaction of an arylindium reagent and two alkyne molecules that affords a substituted naphthalene derivative in moderate to good yield. The reaction represents a new example of iron-catalyzed C–C bond forming reactions via C–H bond functionalization.     

Synthesis and Evaluation of Antimicrobial Activity of Some Novel Heterocyclic Compounds from 5‐Bromosalicylaldehyde

A novel series of coumarins, thiadiazoles, thiazoles, and pyridines were synthesized via reaction of 5‐bromosalicylaldehyde with different reagents. Thus, 5‐bromosalicylaldehyde 1 was reacted with compounds 2a–d affording iminocoumarins 3a–d , which on hydrolysis with 10% hydrochloric acid, afforded coumarins 4a–d , respectively. On the other hand, reaction of 1 with benzylhydrazinecarbodithioate 5 afforded derivative 6 , which reacted with hydrazonoyl halides 7a–f , afforded 1,3,4‐thiadiazoles 11a–f , respectively. Moreover, thiazoles 15 and 16 were obtained via reaction of 1 with thiocarbohydrazide 13 and hydrazonoyl halides. However, condensation of 2‐acetyl‐5‐bromobenzofuran 17 with benzaldehyde afforded chalcone 18 , which reacted with pyridiniumbromides 19a–c , afforded pyridines 20a–c , respectively. Furthermore, pyridines 21–24 were synthesized from the reaction of chalcone 18 with different active methylene compounds. Reaction of 24 with ethylchloroacetate, chloroacetone, and chloroacetonitrile afforded thienopyridines 26a–c , respectively. The structures of the newly synthesized compounds were established based on their spectral data and elemental analyses. Also, selected newly synthesized compounds were screened for their antimicrobial activity against various microorganisms by disk diffusion method.     

The kinetics of the epoxy amine cure reaction from a solvation perspective

This article investigates the role of solvation effects in the autocatalysis reaction of the epoxy–amine cure reaction. A single‐phase three component model was developed encompassing a two‐component reaction mix and a single polymeric product. The reaction was modelled as an S_N2 reaction. Association of the nucleophile with each component in the reaction was defined via a binding constant. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3579–3586, 2004     

Practical Synthesis of 2,3,4,5‐Tetramethoxytoluene

The title compound, a key material for synthesis of coenzyme Q₁₀, was effectively prepared in high yield by a reaction sequence starting from 3,4,5‐trimethoxybenzadehyde via Wolff–Kishner reduction, Vilsmeier–Haack reaction, Dakin reaction, and methylation.     

Acid-catalyzed hydroxymethylation of benzamide with formaldehyde

Hydroxymethylation of benzamide with formaldehyde was investigated in the pH regions of 0.6–6.7 by use of the sulfite method. Investigation of the dependence of the second-order rate constant of the hydroxymethylation k on pH revealed that k decreased with increasing acidity from pH 6.7, became approximately constant at pH 4.5–5.5 (minimum rate), and then increased with increasing acidity. The rate equation showing the pH dependence of k was drawn from the reaction mechanism, and theoretical curves denoting this rate equation and the corresponding observed curves were compared. It was found that the hydroxymethylation is a reaction between a molecule of benzamide and the conjugate acid of formaldehyde (methylol cation) in the region below ca. pH 2.5, and the parallel reaction of a molecule of benzamide with methylol cation and a molecule of formaldehyde (HCHO) in the pH region of 2.5–4.0; in the region of ca. pH 4.5–5.5 the reaction is that between a molecule of benzamide and a molecule of formaldehyde, and the reaction in the pH region 5.5–6.7 is a parallel reaction of a molecule of formaldehyde with the conjugate base and a molecule of benzamide.     

Diesel soot oxidation by nitrogen dioxide,oxygen and water under engine exhaust conditions: Kinetics data related to the reaction mechanism

Experimental studies on diesel soot oxidation under a wide range of conditions relevant for modern diesel engine exhaust and continuously regenerating particle trap were performed. Hence, reactivity tests were carried out in a fixed bed reactor for various temperatures and different concentrations of oxygen, NO₂ and water (300–600 °C, 0–10% O₂, 0–600 ppm NO₂, 0–10% H₂O). The soot oxidation rate was determined by measuring the concentration of CO and CO₂ product gases. The parametric study shows that the overall oxidation process can be described by three parallel reactions: a direct C–NO₂ reaction, a direct C–O₂ reaction and a cooperative C–NO₂–O₂ reaction. C–NO₂ and C–NO₂–O₂ are the main reactions for soot oxidation between 300 and 450 °C. Water vapour acts as a catalyst on the direct C–NO₂ reaction. This catalytic effect decreases with the increase of temperature until 450 °C. Above 450 °C, the direct C–O₂ reaction contributes to the global soot oxidation rate. Water vapour has also a catalytic effect on the direct C–O₂ reaction between 450 °C and 600 °C. Above 600 °C, the direct C–O₂ reaction is the only main reaction for soot oxidation. Taking into account the established reaction mechanism, a one-dimensional model of soot oxidation was proposed. The roles of NO₂, O₂ and H₂O were considered and the kinetic constants were obtained. The suggested kinetic model may be useful for simulating the behaviour of a diesel particulate filter system during the regeneration process.