One-pot synthesis of thia-Michael products from thio acids, epoxides, and electron-deficient alkenes promoted by a silica gel/Et3N combined catalyst

An efficient method for the one-pot production of thia-Michael adducts using thio acids, epoxides, and electron-deficient alkenes is described. Epoxides quickly underwent nucleophilic ring-opening with thio acids on the silica gel surface at room temperature under solvent-free conditions to yield β-hydroxy thioester intermediates. After addition of an electron-deficient alkene and a catalytic amount of Et₃N to the reaction mixture, the β-acyloxy mercaptans were generated in situ and subsequently underwent thia-Michael addition reactions to produce the corresponding adducts in good to excellent yields.     

在中性条件下用亚氯酸钠和双氧水氧化芳香醛

本文优化了中性环境中亚氯酸钠和双氧水氧化醛的反应条件,采用正交实验设计法考察了溶剂、亚氯酸钠和双氧水的用量以及反应温度对醛氧化产率的影响,确定最佳工艺条件为以乙醇作溶剂,亚氯酸钠、双氧水、醛的摩尔比为1.1: 2: 1。在优化的反应条件下对醛进行底物扩展验证其适应性,并通过放大实验说明其工业生产适用性,本方法具有产率高、后处理简单、副产物绿色无污染的优点。     

Highly stereoselective method to prepare bis-phenylchalcogen alkenes via addition of chalcogenolate to phenylseleno alkynes

The preparation of bis-phenylchalcogen alkenes starting from phenylseleno alkynes is described. The nucleophilic species of selenium, tellurium and sulfur were generated in situ from the reaction of the respective diphenyl dichalcogenide with NaBH₄ in PEG-400 as solvent. The chalcogenolate anions were efficiently and selectively added to a variety of phenylselenoalkynes at mild conditions, furnishing the respective (Z)-1,2-bis-phenylchalcogen alkenes in good yields.     

The rearrangement route to 2-azabicyclo[2.1.1]hexanes. Solvent and electrophile control of neighboring group participation

The reactions of N-(alkoxycarbonyl)-2-azabicyclo[2.2.0]hex-5-enes 5 with halonium ion electrophiles were studied in polar and nonpolar aprotic solvents and also in protic media with the aim of controlling nitrogen neighboring group participation. Specifically, for bromonium ions nitrogen participation is facilitated by the polar aprotic solvent nitromethane and by the poorly nucleophilic protic solvent acetic acid. Alkene 5b and bromine/nitromethane afford only the rearranged anti,anti-5,6-dibromo-2-azabicyclo[2.1.1]hexane 6b, and NBS/acetic acid gives an 8:1 mixture favoring rearranged 5-bromo-6-acetate 6f. Conversely, pyridinium bromide perbromide/CH(2)Cl(2) is selective for only unrearranged 5,6-dibromide 7. Iodonium and phenylselenonium ions react with alkenes 5 to give only unrearranged 1,2-addition products 9 and 10, regardless of solvent. Chloronium and fluoronium ions react with alkenes 5 to give 4-aminomethyl-3-hydroxycyclobutene 11, derived by ring cleavage.     

Determination of metals in phospholipids by atomic-absorption spectrophotometry

A procedure is described for the determination of sodium, potassium, calcium, magnesium and manganese in phospholipids by atomic-absorption spectrophotometry. The method uses a solution of phospholipid in isopentyl acetate; phosphate interference is controlled by the addition of aqueous lanthanum chloride solution homogenized with ethanol. Standards are prepared in a similar solvent mixture. A comparison between the described method and that of standard additions show it to be free of phospholipid matrix effects.     

Determination of sorbic acid with sodium chlorite

A new method for the determination of sorbic acid is proposed, using sodium chlorite in hydrochloric add medium as reagent. In these conditions the hydrochloric acid is oxidized to chlorine which adds on to the double bonds of the sorbic acid. The addition is rapid (30-90 sec) and for this reason the determination is more rapid then others similar to it. Sorbic acid has been determined in foods by this method, after a preliminary solvent extraction or steam-distillation.     

Diastereoselective [3+2] Annulation of Aromatic/Vinylic Amides with Bicyclic Alkenes through Cobalt‐Catalyzed C−H Activation and Intramolecular Nucleophilic Addition

A highly diastereoselective method for the synthesis of dihydroepoxybenzofluorenone derivatives from aromatic/vinylic amides and bicyclic alkenes is described. This new transformation proceeds through cobalt‐catalyzed C?H activation and intramolecular nucleophilic addition to the amide functional group. Transition‐metal‐catalyzed C?H activation reactions of secondary amides with alkenes usually lead to [4+2] or [4+1] annulation; to the best of our knowledge, this is the first time that a [3+2] cycloaddition is described in this context. The reaction proceeds under mild conditions and tolerates a wide range of functional groups. Mechanistic studies imply that the C?H bond cleavage may be the rate‐limiting step.     

Triphenylarsine-Catalyzed Cyclopropanation: Highly Stereoselective Synthesis of Trans -2,3-Dihydro-Spiro[Cyclopropane-1,2′-Indan-1′,3′-dione] from Alkene and Phenacyl Bromide

The triphenylarsine-catalyzed approach for the highly stereoselective synthesis of trans-2,3-dihydro-spiro[cyclopropane-1,2′-indan-1′,3′-dione] with alkenes and phenacyl bromide in organic solvent is described. The triphenylarsine-catalyzed cyclopropanation in water was investigated. The mixture of cis/trans isomers is provided with water as a solvent. The cis isomer is formed using water as a solvent. The reactivity of the reaction in water is higher than that in the organic solvent.     

Organoselenium-catalyzed enantioselective syn-dichlorination of unbiased alkenes

The enantioselective dichlorination of alkenes is a continuing challenge in organic synthesis owing to the limitations of selective and independent antarafacial delivery of both electrophilic chlorenium and nucleophilic chloride to an olefin. Development of a general method for the enantioselective dichlorination of isolated alkenes would allow access to a wide variety of polyhalogenated natural products. Accordingly, the enantioselective suprafacial dichlorination of alkenes catalyzed by electrophilic organoselenium reagents has been developed to address these limitations. The evaluation of twenty-three diselenides as precatalysts for enantioselective dichlorination is described, with a maximum e.r. of 76:24 Additionally, mechanistic studies suggest an unexpected Dynamic Kinetic Asymmetric Transformation (DyKAT) process may be operative.     

Investigations of the Mechanism of Alternating Copolymerization with Charge-Transfer Interaction of the Monomers

The applicability of the method of Giese to the measurement of the influence of monomer reactivity is examined. The reaction of alkyl mercuric salts with sodium borohydride permits the production of alkyl (cyclohexyl and butyl) radicals. Since hydrogen radicals are present in high concentration, the addition of alkenes to the reaction mixture leads to radicals from the alkenes. Further addition of alkene (polymerization) can be nearly completely excluded in this way. The composition of the reaction products is determined by gas chromatography. The addition rate of the alkenes relative to styrene allows correlation with the e value of the Q-e scheme of Alfrey and Price. The method answers the question of how far addition of the monomer complex occurs in one step or as separate addition of both monomers during copolymerization in the presence of charge-transfer (CT) complexes of the monomers. The investigations are performed by using the styrene/acrylonitrile/ZnCl₂system, and it is demonstrated that the reactivity of the complexed     

Reaction of a triazolinedione with simple alkenes. Isolation and characterization of hydration products

The reaction of N-phenyltriazolinedione with three simple alkyl-substituted alkenes in water/alcohol or water/acetone solution was found to give a mixture of the corresponding ene and water addition products. The new hydration products were characterized by spectroscopy, and in one case, also by X-ray diffraction analysis. Thermodynamic parameters were determined for the reactions involving 2-methylbut-2-ene, TriME, and 2,3-dimethylbut-2-ene, TetraMe, in accordance with an ‘S_N2-like’, nucleophilic attack on a closed aziridinium imide (AI) intermediate by water.     

Catalyst free conjugate addition of indoles and pyrroles to nitro alkenes under solvent free condition (SFC): an effective greener route to access 3-(2-nitro-1-phenylethyl)-1H-indole and 2-(2-nitro-1-phenylethyl)-1H-pyrrole derivatives

Catalyst free conjugate addition of reactive hetero aromatics (pyrrole and indoles) to nitro alkenes under solvent free condition is described. This method provides several advantages, such as operational simplicity, solvent-free conditions and good yields of products. Also it is environmentally friendly and more cost effective alternative to existing protocols.     

Rhodium phosphine-π-arene intermediates in the hydroamination of alkenes

A detailed mechanistic study of the intramolecular hydroamination of alkenes with amines catalyzed by rhodium complexes of a biaryldialkylphosphine is reported. The active catalyst is shown to contain the phosphine ligand bound in a κ(1), η(6) form in which the arene is π-bound to rhodium. Addition of deuterated amine to an internal olefin showed that the reaction occurs by trans addition of the N-H bond across the C═C bond, and this stereochemistry implies that the reaction occurs by nucleophilic attack of the amine on a coordinated alkene. Indeed, the cationic rhodium fragment binds the alkene over the secondary amine, and the olefin complex was shown to be the catalyst resting state. The reaction was zero-order in substrate, when the concentration of olefin was high, and a primary isotope effect was observed. The primary isotope effect, in combination with the observation of the alkene complex as the resting state, implies that nucleophilic attack of the amine on the alkene is reversible and is followed by turnover-limiting protonation. This mechanism constitutes an unusual pathway for rhodium-catalyzed additions to alkenes and is more closely related to the mechanism for palladium-catalyzed addition of amide N-H bonds to alkenes.     

Reaction of Sulfinic Acids with Heteroconjugated Alkenes

Abstract

The nucleophilic addition reactions of arenesulfinic acids with heteroconjugated alkenes have been studied. The structures of the sulfones thus obtained were confirmed by microanalytical and spectral methods. Kinetic parameters of the nucleophilic addition reactions were determined. Interactions are second-order reactions, but they are first order regarding each reagent. The influence of various substituents at the carbon–carbon double bond on the nucleophilic activity was studied.     

Cascade Multicomponent Synthesis of Indoles,Pyrazoles, and Pyridazinones by Functionalization of Alkenes

The development of multicomponent reactions for indole synthesis is demanding and has hardly been explored. The present study describes the development of a novel multicomponent, cascade approach for indole synthesis. Various substituted indole derivatives were obtained from simple reagents, such as unfunctionalized alkenes, diazonium salts, and sodium triflinate, by using an established straightforward and regioselective method. The method is based on the radical trifluoromethylation of alkenes as an entry into Fischer indole synthesis. Besides indole synthesis, the application of the multicomponent cascade reaction to the synthesis of pyrazoles and pyridazinones is described.     

用离子色谱法测定水中的二氧化氯、氯、亚氯酸根及氯酸根

建立了一种测定水中的ClO2、Cl2、ClO2^-、ClO3^-离子色谱法,在含有碳酸氢钠缓冲溶液的中性条件下,用NaNO2将ClO2、Cl2还原为ClO2^-、Cl^-,通过测定ClO^-和NO3^-的变化值,间接测定ClO2和Cl2。加入硫代乙酰胺(TAA)作掩蔽剂测定ClO2^-。     

Nickel-catalyzed carbonylative cycloaddition of allyl halides and alkenes

The carbonylative addition between allyl halides and alkenes is described. The [2+2+1] reaction is catalyzed by Ni(I), and takes place with different strained alkenes under very mild conditions. Changes in solvent and use of different amounts of water in the reaction produce changes on the final products obtained.     

The unprecedented reaction of dimethylsulfonium methylide with Michael acceptors: synthesis of 1-substituted vinyl silanes and styrenes

Rather than the usual cyclopropanation, conditions for an unprecedented elimination reaction from the adduct of dimethylsulfonium methylide and various Michael acceptors have been established leading to functionalized 1-substituted alkenes. In silyl substituted substrates (2a and 2h), where a facile Peterson-type olefination is possible from the adduct; elimination took place instead to give functionalized 1-substituted vinyl silanes. Aryl substituted Michael acceptors (2b-e, 2g and 2i-k) also underwent a similar kind of olefination to give 1-substituted styrene derivatives with moderate yields along with a side product, which arose by nucleophilic demethylation from the adduct of dimethylsulfonium methylide and arylidene malonates. Hammett studies revealed that selectivity for olefination vs. demethylation increases as the aryl substituent becomes more electron deficient. Alkylidene malonates (2f and 2l) with a beta-alkyl substituent did not favour the olefination process. Sequential addition of Michael acceptors and alkyl halides to a mixture of dimethylsulfonium methylide and sodium dimsylate provided olefination followed by alkylation on the active methine group. A mechanistic pathway has been formulated from the studies of a few sulfonium methylides.     

A Cooperative Strategy for the Highly Selective Intermolecular Oxycarbonylation Reaction of Alkenes using a Palladium Catalyst

A novel method for intermolecular functionalization of terminal and internal alkenes has been designed. The electrophilic reagent, hypervalent iodine, plays a key role in this process by activating the alkene C=C bond for nucleophilic addition of the palladium catalyst. This process generates an iodonium‐containing palladium species which undergoes CO insertion. The new approach, intermolecular oxycarbonylaton reactions of alkenes, has been achieved and carried out under mild reaction conditions to produce the corresponding β‐oxycarbonylic acids with excellent efficiencies and levels of regio‐ and diastereoselectivity.     

Bifunctional Heterogeneous Catalysis of Silica–Alumina‐Supported Tertiary Amines with Controlled Acid–Base Interactions for Efficient 1,4‐Addition Reactions

We report the first tunable bifunctional surface of silica–alumina‐supported tertiary amines (SA–NEt₂) active for catalytic 1,4‐addition reactions of nitroalkanes and thiols to electron‐deficient alkenes. The 1,4‐addition reaction of nitroalkanes to electron‐deficient alkenes is one of the most useful carbon–carbon bond‐forming reactions and applicable toward a wide range of organic syntheses. The reaction between nitroethane and methyl vinyl ketone scarcely proceeded with either SA or homogeneous amines, and a mixture of SA and amines showed very low catalytic activity. In addition, undesirable side reactions occurred in the case of a strong base like sodium ethoxide employed as a catalytic reagent. Only the present SA‐supported amine (SA–NEt₂) catalyst enabled selective formation of a double‐alkylated product without promotions of side reactions such as an intramolecular cyclization reaction. The heterogeneous SA–NEt₂ catalyst was easily recovered from the reaction mixture by simple filtration and reusable with retention of its catalytic activity and selectivity. Furthermore, the SA–NEt₂ catalyst system was applicable to the addition reaction of other nitroalkanes and thiols to various electron‐deficient alkenes. The solid‐state magic‐angle spinning (MAS) NMR spectroscopic analyses, including variable‐contact‐time ¹³C cross‐polarization (CP)/MAS NMR spectroscopy, revealed that acid–base interactions between surface acid sites and immobilized amines can be controlled by pretreatment of SA at different temperatures. The catalytic activities for these addition reactions were strongly affected by the surface acid–base interactions.