Rh(I)-Catalyzed Asymmetric Hydrosilylation and Hydroboration/Oxidation Reactions Using Berens Ligand

The Berens ligand 2 was used in a number of Rh(I)-catalyzed asymmetric hydrosilylations of acetophenones under standard conditions, affording the corresponding 1-arylalcohols in ees up to 65%. Some novel Rh catalysts were generated in situ from the neutral precatalyst [Rh(µ-Cl)(COD)]₂ and screened in the catalytic asymmetric hydroboration/oxidation of styrenes, gave enantioselectivities of up to 62%.     

A simple Lewis acid induced reaction of phenols with electrophiles: Synthesis of functionalized 4H-chromenes and ortho-benzylphenols

Abstract

Lewis acid ZnCl₂ promoted cyclization protocol to 4H-chromenes is accomplished, using readily available phenols and acetophenones as starting materials. Interestingly, the process is feasible under the solvent free environment. Synthesis of a variety of 4H-chromenes have been accomplished using this strategy. In addition, this concept is extended to the synthesis of ortho-benzylphenols by treating phenols either with styrenes or secondary benzylic alcohols.     

New iminophosphine–Ru(II) complexes and their application in hydrogenation and transfer hydrogenation

Ruthenium complexes [RuCl₂L₂] were prepared by treating [RuCl₂(p‐cymene)]₂ with structurally similar N‐(2‐(diphenylphosphino)benzylidene)‐3‐methylpyridin‐2‐amine, 4‐(2‐(diphenylphosphino)benzylideneamino)‐3‐methylphenol and 4‐(2‐(2‐(diphenylphosphino)benzylideneamino)ethyl)phenol refluxed in toluene. These complexes were used as catalysts for the transfer hydrogenation of acetophenones in 2‐propanol and for the direct hydrogenation of styrenes under hydrogen pressure. The results of the catalytic studies provide evidence that these complexes function as excellent catalysts for hydrogenation and transfer hydrogenation. Copyright © 2014 John Wiley & Sons, Ltd.     

Solvohyperiodination. A comparison with solvothallation

C₆H₅IO/CH₃OH and a catalyst such as FSO₃H , CF₃SO₃H or BF₃-Et₂O as well as C₆H₅(OH)OTs-CH₃OH,react with chalcones, acetophenones and styrenes to yield rearranged products. The overall course of these reactions is analogous to that of Tl(NO₃)₃-CH₃OH in reaction with the same compounds.     

Epoxidation of styrenes with the peroxidase from the cultured cells of Nicotiana tabacum

An enzyme concerned with the epoxidation of styrenes was isolated from cultured cells of Nicotiana tabacum. The enzyme had peroxidase activity as well as epoxidation activity, and its amino acid sequence showed 89% homology in their 9 amino acid overlap with horseradish peroxidase. In the enzymatic reaction, hydrogen peroxide and p-cresol were necessary and molecular oxygen was the source of the oxygen atom of the epoxide. The enzymatic reaction using a spin trap reagent and monitoring of the reaction with ESR indicated that the epoxidation reaction of styrenes proceeded by a radical mechanism with peroxidase.     

Selective initiation of nonconjugated dienes containing electron donor–electron acceptor systems. IV. Polymerization of vinyl ether–styrene monomers

Three isomeric nonconjugated dienes, o-, m- and p-(2-vinyloxyethoxy)styrenes, were selectively polymerized by anionic or radical initiators through the styryl double bond while leaving the vinyl ether moiety intact. The anionic-initiated polymeric products are of high molecular weight and narrow molecular weight distribution as characterized by membrane osmometry and gel-permeation chromatography, respectively. These polymers were subsequently crosslinked by cationic initiators via the vinyl ether moiety on the polymer side chains. Acid-catalyzed hydrolysis of the poly(2-vinyloxyethoxy)styrenes yielded their respective hydroxy-containing polymers, polyvinylphenoxyethanols. The latter were physically and spectroscopically identical to authentic samples prepared by radical polymerization of the corresponding vinylphenoxyethanols, which, in turn, were synthesized by hydrolysis of the (2-vinyloxyethoxy)styrenes. The polyvinylphenoxyethanols were shown to undergo many chemical transformations, such as esterification with 3,5-dinitrobenzoyl chloride, cyanoethylation, and urethane formation.     

Torsional barriers for planar versus twisted singlet styrenes

Kinetic modeling of the temperature-dependent lifetimes of styrene and several methyl-substituted styrenes has been used to obtain the torsional barriers for singlet-state C=C rotation. The barrier for C=C torsion is found to be correlated with the ground-state phenyl-vinyl dihedral angle, varphi, planar styrenes having barriers of approximately 6.5 kcal/mol and moderately twisted styrenes having smaller barriers. Highly twisted styrenes undergo exceptionally rapid intersystem crossing. This unexpected dependence of excited-state behavior on varphi is attributed to a change in the character of the excited states from delocalized for planar styrenes to localized for highly twisted styrenes.     

Synthesis,characterization and decomposition of 2-aryl-2-hydroxyethylcobaloximes

2-Phenyl-2-hydroxyethyl(aquo)cobaloxime(Ia) and the p-methyl (Ib) and p-cyano (Ic) derivatives have been synthesized and characterized. The parent compound and the p-methyl derivative decompose spontaneously both in the solid state and in methanol to give mixtures of the appropriate styrenes and acetophenones. Kinetics and product ratios of the decomposition of Ia and Ib in methanol have been studied as a function of temperature. Evidence is presented that both reaction pathways are ionic in nature and that an intermediate (presumed to be a phenethylcobaloxime carbonium ion) is involved in the styrene forming pathway. Acetophenones are apparently formed via a 1,2-hydride shift mechanism with solvent acting as a general base. Both reaction pathways show a large substituent effect with electron donating substituents increasing reactivity, Ic proved to be extraordinarily stable in methanol but decomposed readily in aqueous sulfuric acid to produce primarily p-cyanoacetophenone. Kinetic evidence for formation of a cationic intermediate is presented.     

Selective Functionalization of Styrenes with Oxygen Using Different Electrode Materials: Olefin Cleavage and Synthesis of Tetrahydrofuran Derivatives

Electrode materials can have a significant impact on the course of an electrolysis reaction. Of particular interest is that different electrodes can generate different products from the same substrate. The electrode‐material‐selective transformations of styrene derivatives with molecular oxygen are reported. Platinum electrodes afford carbonyl products via cleavage of olefins, whereas tetrahydrofuran formation is achieved with carbon electrodes. A variety of different styrenes are available for both reactions. Electrolysis allows straightforward and mild chemical conversions that are metal‐ and oxidant‐free. Electrochemical measurements illuminate the different effects of platinum and carbon electrodes on styrenes. The key to the differing reactions is probably that the oxidation potentials of the substrates are lower (higher HOMO energy) on carbon electrodes than on platinum electrodes. The adsorption of the substrates on carbon electrodes can also promote tetrahydrofuran formation.     

Semi-empirical π-electron calculations of proton,nitrogen and fluorine hyperfine-coupling constants

The application of the parameterization scheme of Beveridge and Hinze for π-electron molecular orbital calculations to spin density calculations is examined for a series of radicals including anions derived from pyridine derivatives, substituted styrenes, aromatic carboxylic acids, benzonitriles and fluoronitrobenzene derivatives and azabenzyl and fluorobenzyl radicals. The method correlates proton hyperfine coupling constants satisfactorily and gives a reasonable correlation of nitrogen coupling constants. The application to fluorine couplings is less satisfactory.     

Spontaneous reactions of electron‐accepting substituted quinodimethane with substituted styrenes: Inductive and steric effects on the formation of a zwitterionic intermediate

Spontaneous reactions of an electron‐accepting substituted quinodimethane, 1‐(2,2‐dimethyl‐1,3‐dioxane‐4,6‐dione‐5‐ylidene)‐4‐(dicyanomethylene)‐2,5‐cyclohexadiene, with p‐substituted, α‐substituted, and β‐substituted styrenes were investigated. When p‐substituted styrenes were used as comonomers, no spontaneous reactions took place for styrenes with an electron‐accepting p substituent such as COOMe and CN groups, and both terpolymers and cycloadducts were formed for the other p‐substituted styrenes. When α‐substituted and β‐substituted styrenes were used as comonomers, no reactions occurred for α‐ and β‐substituted styrenes with a bulky phenyl group, and spontaneous reactions took place for those with a smaller methyl group. The reaction products were an alternating copolymer for α‐substituted styrene and both terpolymers and 5‐ethylidene‐2,5‐dimethyl‐1,3‐dioxane‐4,6‐dione for β‐substituted styrenes. The position of the methyl group in the styrenes significantly affected the product formation. This behavior in the spontaneous reactions was discussed on the basis of the ability of formation of the zwitterionic tetramethylene intermediate and its conformation, determined by polar and steric effects of the substituents in the substituted styrenes. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5195–5206, 2005     

新颖、无金属、高效分子碘催化的苯乙烯氢化芳基化反应

本文通过使用单质碘作为催化剂,在室温无溶剂的条件下研究了各种芳烃和不同苯乙烯衍生物的氢化芳基化反应,并能以较高的收率得到一系列1,1－二芳基甲烷衍生物。本合成策略避免了重金属的使用,提供了对环境友好的高效合成方法。     

NBS-assisted an efficient conversion of styrenes to α-hydroxy ketones in water

An expedient, mild and environmentally benign method for the oxidation of styrenes to α-hydroxy ketones has been developed. This conversion has been achieved by employing water as a solvent as well as an oxygen source. This facile and efficient tandem process provides α-hydroxy ketones in moderate to good yields from easily accessible styrenes.     

使用DBDMH和Et3N·3HF的苯乙酮一锅法α-亲核氟代

报道一种通过溴代和氟代的一锅法操作,从苯乙酮直接制备α-氟代苯乙酮的新方法.使用1,3-二溴-5,5-二甲基海因(DBDMH)作为溴代试剂,三乙胺三氟化氢作为氟代试剂,除了p-和m-硝基苯乙酮之外,α-氟代苯乙酮以82%～87%的收率被获得.本方法使用的试剂价廉、收率较高、操作简单方便,有较高的应用价值.     

General and practical one-pot synthesis of dihydrobenzosiloles from styrenes

A one-pot synthesis of dihydrobenzosiloles from styrenes has been developed. The reaction involves the nickel-catalyzed hydrosilylation of styrene with diphenylsilane, followed by the iridium-catalyzed dehydrogenative cyclization. This method is efficient for both electron-rich and -deficient styrenes and exhibits good functional group tolerance, as well as excellent regioselectivity. The forming dihydrobenzosiloles can be efficiently converted into valuable benzosiloles or 2-hydroxyphenethyl alcohols.     

Visible‐Light‐Mediated [4+2] Cycloaddition of Styrenes: Synthesis of Tetralin Derivatives

We report a formal [4+2] cycloaddition reaction of styrenes under visible‐light catalysis. Two styrene molecules with different electronic or steric properties were found to react with each other in good yield and excellent chemo‐ and regioselectivity. This reaction provides direct access to polysubstituted tetralin scaffolds from readily available styrenes. Sophisticated tricyclic and tetracyclic tetralin analogues were prepared in high yield and up to 20/1 diasteroselectivity from cyclic substrates.     

Copper(I)‐Catalyzed Enantio‐ and Diastereodivergent Borylative Coupling of Styrenes and Imines

We report copper(I)‐catalyzed enantio‐ and diastereodivergent borylative coupling of styrenes and imines to produce enantiomerically‐enriched α,β‐dibranched γ‐boryl amine derivatives. Each of the four possible stereoisomers of the products, derived from the two contiguous stereocenters, was selectively accessible by choosing a proper chiral ligand for the copper catalyst. This method, which combines catalyst‐controlled stereodivergency and constitutional divergency derived from the lynchpin motif (i.e., the C?B bond), offers a strategy for addressing the construction of molecular structural diversity concomitant with precise chirality control.     

Switchable Chemoselectivity of Reactive Intermediates Formation and Their Direct Use in A Flow Microreactor

A chemoselectivity switchable microflow reaction was developed to generate reactive and unstable intermediates. The switchable chemoselectivity of this reaction enables a selection for one of two different intermediates, an aryllithium or a benzyl lithium, at will from the same starting material. Starting from bromo-substituted styrenes, the aryllithium intermediates were converted to the substituted styrenes, whereas the benzyl lithium intermediates were engaged in an anionic polymerization. These chemoselectivity-switchable reactions can be integrated to produce polymers that cannot be formed during typical polymerization reactions.     

Visible-Light-Mediated [4+2] Cycloaddition of Styrenes: Synthesis of Tetralin Derivatives

We report a formal [4+2] cycloaddition reaction of styrenes under visible-light catalysis. Two styrene molecules with different electronic or steric properties were found to react with each other in good yield and excellent chemo- and regioselectivity. This reaction provides direct access to polysubstituted tetralin scaffolds from readily available styrenes. Sophisticated tricyclic and tetracyclic tetralin analogues were prepared in high yield and up to 20/1 diasteroselectivity from cyclic substrates.     

Olefin Bifunctionalization: A Visible‐light Photoredox‐catalyzed Aryl Alkoxylation of Olefins

Olefin bifunctionalization is a facile route to obtain complex molecules from abundant and commercially available olefin feedstocks. Visible light together with a catalytic amount of tris(bipyridine)ruthenium salt catalyzes the aryl alkoxylation of styrenes with aryl diazonium salts in alcohol solvents via a photoredox process. The scope of this proposed reaction with respect to various aryl diazonium salts and styrenes has been investigated.