P-Dodecylbenzenesulfonic acid(DBSA),a Brфnsted acid-surfactant catalyst for Biginelli reaction in water and under solvent free conditions

We report herein the use of p-dodecylbenzenesulfonic acid(DBSA) as a catalyst for a one-pot Biginelli reaction to afford 3,4- dihydropyrimidinone derivatives in good to excellent yields.This reaction proceeds efficiently in water and under solvent free conditions.Comparisons of results indicate that although the yields are high and comparable for both methods,the reaction times are considerably shorter under solvent free conditions.     

Three-Component Reaction of Triphenylphosphine,Dialkyl Acetylenedicarboxylates,and Heterocyclic Rings and the Related Iminophosphoranes

Crystalline phosphorus ylides are obtained in excellent yields from the 1:1:1 addition reaction of triphenylphosphine, dialkyl acetylenedicarboxylate, and NH acids, such as 2-aminothiazole and 2-aminobenzothiazole. These stabilized phosphoranes undergo a smooth intramolecular reaction in boiling toluene to produce aryliminophosphoranes in excellent yields.     

Rh-Catalyzed One-Pot Reductive Alkylation of Malononitrile Under Transfer Hydrogenation Conditions

Dihydroartemisinin can be converted to its ether derivatives in good yields by reaction with different alcohols in the presence of a catalytic amount of dodecatungstophosphoric acid hydrate. Easy handling, trouble-free workup by filtration, excellent yields, and very short reaction times are some of the highlights of this protocol.     

Amberlite-IR 120 catalyzed three-component synthesis of α-amino phosphonates in one-pot

A simple, efficient, and environmentally benign method for a three-component reaction of an amine, an aldehyde or a ketone, and diethyl phosphite catalyzed by Amberlite-IR 120 resin has been developed to afford α-amino phosphonates in high yields and short reaction times under solvent-free reaction conditions. The major advantages of the present method are good yields, inexpensive, ecofriendly and reusable catalyst, mild and solvent-free reaction conditions and tolerance towards various functionalities present in the substrates.     

An improved synthesis of cyclopropanes from stabilized phosphonates and 1,2-dioxines

Addition of stabilized Horner-Wadsworth-Emmons (HWE) phosphonates to substituted 1,2-dioxines leads to diastereomerically pure di- and trisubstituted cyclopropanes in high yields and represents a viable alternative to ylides in the cyclopropanation reaction involving 1,2-dioxines. While yields are comparable, reaction times with these stabilized phosphonates were accelerated and the diastereoselectivity for this cyclopropanation reaction was significantly greater than for the previously reported examples employing ylides.     

Regio- and stereoselective route to tetrasubstituted olefins by the palladium-catalyzed three-component coupling of aryl iodides, internal alkynes, and arylboronic acids

[reaction: see text] The Pd-catalyzed three-component coupling of readily available aryl iodides, internal alkynes, and arylboronic acids provides a convenient, one-step, regio- and stereoselective route to tetrasubstituted olefins in good to excellent yields, although electron-poor aryl iodides and dialkylalkynes normally afford only low yields under our standard reaction conditions. The proper combination of substrates and reaction conditions is important for high yields. The presence of water generally substantially increases the yields of the desired tetrasubstituted olefins. The reaction involves cis-addition of the aryl group from the aryl iodide to the less hindered or more electron-rich end of the alkyne, while the aryl group from the arylboronic acid adds to the other end. A modified, room-temperature procedure has also been successfully developed, which works very well for some substrates. Tamoxifen and its derivatives are synthesized in a concise, regio- and stereoselective manner by applying our synthetic protocol.     

Envirocat EPZ-10: A Solid Acid Catalyst for the Synthesis of 1,8-Dioxo-octahydroxanthenes in Aqueous Medium

An efficient method for synthesis of 1,8-dioxo-octahydroxanthenes using EPZ-10 as a heterogeneous catalyst is developed. In this method, aldehydes and dimedone / cyclohexane-1,3-dione are heated at 70 °C in the presence of a catalytic amount of EPZ-10 in water as a universal solvent, affording the corresponding 1,8-dioxo-octahydroxanthenes in moderate to excellent yields. Also, domino Knoevenagel / hetero-Michael-addition reaction is described in water without any catalyst with excellent yields. The major advantages of this method are excellent yields, short reaction time, and ease of operation. This green protocol works well with dimedone as well as cyclohexane-1,3-dione.     

Synthesis of Some New Scaffolds of Amino Isoxazolidines and Their Further Functionalization into New Class of Peptides: A New Approach

Some new class of amino isoxazolidine derivatives have been synthesized from α‐amino nitrones in water with good to excellent yields. The new isoxazolidines are further functionalized into new scaffolds of peptides with good synthetic potentiality. Simple reaction methodology, greener approaches, atom efficiency, noninvolvement of catalysts, faster reaction conditions, excellent yields, and a new approach in peptide synthesis are the attractions in these syntheses.     

THE PHOTOLYSIS OF TRYPTOPHAN IN THE PRESENCE OF OXYGEN

Abstract— Quantum yields for the destruction of tryptophan by a single 500 J flash in aqueous solution have been determined over the pH range 1–13 in both air-equilibrated and nitrogen-saturated conditions. When these quantum yields are compared with the quantum yields for radical formation and photoejection of electrons, it is found that there is good agreement only for the nitrogen-saturated case. In air-equilibrated solutions of tryptophan, there is a large disparity between the measured degradation quantum yields and those for photoejection of electrons and radical formation. Oxygen, therefore, is playing a major role in the photochemical decomposition and it is proposed that the major reaction which occurs, under normal atmospheric conditions, is the reaction of the lowest triplet excited state of tryptophan with oxygen.
Preliminary photolysis-product distributions against pH are discussed, and indicate that a total of nine major products are formed in the presence of oxygen.     

Suzuki-Miyaura cross-coupling reactions of potassium vinyltrifluoroborate with aryl and heteroaryl electrophiles

We have previously reported that the palladium-catalyzed cross-coupling reaction of potassium vinyltrifluoroborate with aryl electrophiles proceeds with good yields. Herein, we describe recent progress in optimizing the reaction, as well as outlining the scope and limitations of the reaction. The cross-coupling reaction can generally be effected using 2 mol % of PdCl2 and 6 mol % of PPh3 as a catalyst system in THF/H2O with Cs2CO3 as a base. Moderate to good yields are obtained in the presence of a variety of functional groups.     

Novel C-C bond cleavage under mild, neutral conditions: conversion of electron-deficient aryl alkyl ketones to aryl carboxylic esters

A novel, unique way to cleave the carbon-carbon bond in aryl alkyl ketones under mild, neutral conditions is described. Treatment of aryl alkyl ketones in a refluxing mixture of N,N-dimethylformamide dimethyl acetal and methanol for 16 h provided aryl carboxylic esters. The scope and limitations of the reaction are discussed. Useful yields of the reaction can be obtained with electron-deficient aryl groups, and the yields are higher when the alkyl group is larger than a methyl group. Studies toward elucidation of the reaction mechanism led to a proposed mechanism that is consistent with all the observations.     

Lead-promoted Barbier-type reaction of aldehydes with propargyl bromides in aqueous media

This paper reports that the reaction of the propargyl bromides with aldehydes promoted by powdered lead in aqueous media.The selectivity and possible mechanism of these reactions are discussed.The yields of products for reaction of propargyl bromide are 31~71%.The ratios of al-lenyl alcohol and homopropargyl alcohol are 1:1.5 to 1:3.The product for reaction of phenyl propargyl bromide is allenyl alcohol and the yields are 52~84%.     

Synthesis of Cyclopropyl Ethers and Cyclopropanols by Carbene Transfer – Acetolysis of Cyclopropyl p-Toluenesulfonates

The reaction of chloromethyl phenyl ether with butyllithium in olefins yields phenoxy-cyclopropanes. 1-Chloro-1-phenoxycyclopropanes can be prepared in a similar manner, though the yields are poor. Alkoxycyclopropanes are formed when dichloromethyl alkyl ethers are treated with methyllithium/lithium iodide in the presence of olefins. Cyclopropanols can be obtained in good yields by reaction of (β-chloroethoxy)cyclopropanes either with butyl- or ethyllithium or with bases. – As was shown by acetolysis experiments with cyclopropyl p-toluenesulfonates having a known steric configuration, the rearrangement of a cyclopropyl derivative into an allyl cation proceeds in accordance with the Woodward-Hoffmann-DePuy rule. The solvolysis of exo-bicyclo[n.1.0]alkyl p-toluene-sulfonates is assumed to proceed via “semi-open” intermediates, which are somewhere between an allyl cation and a cyclopropyl cation.     

Effect of vitamins C and P on the chemiluminescence of lucigenin in model membrane structures

The chemiluminescence quantum yields of the lucigenin light reaction in didodecyldimethylammonium bromide lamelar aggregates are affected by the presence of vitamins C and P. A dramatic lowering of the chemiluminescence quantum yield is observed in the presence of sodiumL-ascorbate, the reaction is virtually unaffected by nicotinamide and the quantum yields are raised by almost a factor of 2 in the presence of sodium nicotinate at high concentrations.     

锡存在下取代的炔丙基溴与醛反应的选择性

报道三甲基硅基和苯基取代的炔丙基溴在锡存在下与醛的反应, 并讨论了反应的选择性。三甲基硅基炔丙基溴与醛的反应产率约为71-84%。产物中丙二烯醇与高炔丙基醇之比在44 :56到25 : 75之间, 苯基炔丙基溴的反应得到了产物丙二烯醇。     

THE PREPARATION OF TRIALKYL PHOSPHITES DIRECTLY FROM THE ELEMENT

Abstract

The reaction between finely divided white phosphorus and several alkoxide ions in the presence of tetrachloromethane and excess of alcohol has been investigated under a variety of conditions. High yields of trialkylphosphite are obtained when two equivalents of alkoxide are used. With one equivalent of alkoxide, dialkylphosphonate is formed in comparable yield. Maximum yields of triester are obtained within 1–3 h at room temperature. Prolonged treatment results in the conversion of trialkylphosphite to phosphate by reaction with tetrachloromethane. Phenolate ions are unreactive under the same experimental conditions. The mechanism of the reaction is discussed.     

Hexamethylenetetraamine-Bromine Catalyzed Rapid and Efficient Synthesis of Bis(indolyl)methanes

Summary. Highly rapid and convenient syntheses of bis(indolyl)methanes in excellent yields were carried out using the inexpensive and easily available catalyst, hexamethylenetetraamine-bromine (HMTAB). Mild reaction conditions, short reaction times, and excellent yields are important features of this method.     

Chemoselective Synthesis of Functionalized 2,5-Dihydro-2-thioxo-1H-imidazoles from 5,5-Diarylthiohydantoins and Activated Acetylenes

Stable crystalline phosphorus ylides are obtained in excellent yields from the 1:1:1 addition reaction between 5,5-diarylthiohydantoins and dialkyl acetylenedicarboxylates in the presence of triphenylphosphine. These phosphoranes undergo a smooth intramolecular Wittig reaction followed by an electrocyclic ring opening to produce dialkyl 2-(2,5-dihydro-5,5-diaryl-2-thioxo-1H-imidazol-4-yl)but-2-enedioates in good yields.     

The palladium-catalysed arylation of activated alkenes with aroyl chlorides

Aroyl chlorides react with activated alkenes in presence of a tertiary amine and a catalytic amount of palladium acetate to give arylated alkenes, specifically cinnamic acid derivatives and stilbenes. The reaction involves a highly efficient decarbonylation of the aroyl chloride. High yields can be obtained at low catalyst concentration by choice of an appropriate base. The reaction is not particularly sensitive to substituents in the aroyl chloride, although strongly electron-donating groups are advantageous (yields up to 98%). With mono-substituted alkenes E-isomers are formed with almost complete specificity. A mechanism for the reaction is proposed.     

Critical assessment of two classical synthetic methods for preparation of thiophene-substituted isoxazoles

Formation of thiophene-substituted isoxazoles by reaction of chalcone dibromides and 1,3-diketones with hydroxylamine hydrochloride has been examined under different conditions. Use of KOH as base in the reaction of dibromide chalcone analogs with hydroxylamine hydrochloride yields mixtures of isomeric isoxazoles in modest yields. Replacement of KOH with pyridine affords negligible amounts of isoxazoles only, the intermediate 2-bromoprop-2-en-1-one being isolated from the reaction as the major product. Substitution of the β-bromine atom from a chalcone dibromides with a methoxy group by solvolysis occurred when no base was used. Mixtures of isomeric isoxazoles in which the isoxazole that had a 2-thienyl group at position 5 were always major components, were obtained in good yields from reaction of thiophene-containing 1,3-diketones with hydroxylamine hydrochloride, irrespective of reaction pH. At low pH, regioselectivity was poorer than that observed for reaction of chalcone dibromides with hydroxylamine hydrochloride, but yields were substantially better. At high pH, yields were comparable with those at low pH and regioselectivity for 3-aryl-5-(2-thiophenyl)isoxazole was slightly enhanced, but the dioxime corresponding to the initial 1,3-diketone was also produced in low yields as a mixture of stereoisomers.