Mild Lewis acids such as Mg(ClO4)2 show a new level of catalytic activity for the decarboxylative esterification of carboxylic acids with commercially available dialkyl dicarbonates. In the presence of as little as one mol % Mg(ClO4)2 catalyst, carboxylic acids can thus easily and near quantitatively be protected at room temperature, e.g., as methyl, benzyl, or t‐butyl esters. Only volatile by‐products are released so that the purification of the products is particularly easy. Many sensitive functionalities are tolerated, including even phenol esters, or free hydroxy and BOC groups. 相似文献
Lewis acid doped polyanilines are prepared by doping of polyaniline base with Lewis acids. Polyaniline base and Lewis acid doped polyanilines are characterized by physical and spectral methods. They are used as catalysts for the first time for acetalization of carbonyl compounds. The catalyzed acetalization of benzaldehyde with propane-1,2-diol is conducted in excellent yields with simple and more environmentally benign procedure. The use of these doped lewis acid catalysts is feasible because of being ecofriendly, their easy preparation, easy recovery, reusability, and good activity. 相似文献
Chiral iron and ruthenium Lewis acids: analogies and differences between the catalysts and the role of the anion in catalytic Diels‐Alder reaction. In short: Fe catalysts are faster but Ru analogues are more stable and can be recovered quantitatively. Rational ligand design is shown to result in a large increase in chiral induction. 相似文献
The binding of Lewis bases to organoboron polymeric Lewis acids has been studied and the parameters that determine the complexation
equilibrium have been investigated, which include (i) the strength of the individual Lewis acids and Lewis bases, (ii) concentration,
and (iii) temperature. While the strongly Lewis acidic borane polymers poly(4-bis(pentafluorophenyl)borylstyrene) (PS-BPf) and poly(4-(di-2-thienylboryl)styrene) (PS-BTh) form isolable complexes with strong Lewis bases such as 4-t-butylpyridine (tPy), a temperature dependent equilibrium is established with weaker bases such as THF. Similarly, the weakly Lewis acidic
boronate polymer poly(4-diethoxyborylstyrene) (PS-BOEt) undergoes a temperature dependent equilibrium with the strong Lewis base 4-dimethylaminopyridine (DMAP), while poly(4-pinacolatoborylstyrene)
(PS-BPin) does not significantly bind to pyridine bases. Decomplexation of PS-BTh·tPy is achieved by treatment with the stronger Lewis acid, B(C6F5)3, thereby confirming the reversible nature of the polymeric Lewis acid–base adducts.
This paper is dedicated to Professor Ian Manners in gratitude of his guidance throughout the years and recognition of his
scientific accomplishments 相似文献
Biodiesel can be produced by transesterification of oil triglycerides, as well as by esterification of fatty acids using feedstock materials rich in free fatty acids)FFAs). Utilization of such feedstocks can gain substantial economical profit and solve a problem of disposal of residual raw materials. To find an effective method of biodiesel production from FFA, we developed esterification of FFAs under ultrasonic activation using Lewis acids as catalysts. Homologous catalyst BF3 and heterogeneous AlCl3 were highly effective in reactions of model FFAs methylation under ultrasonic activation, when the reaction yield reached 100 %. Ethylation at the same conditions was less successful. 相似文献
The field of organocatalysis is growing rapidly and attracts an increasing number of research groups. Most organocatalysts can be classified as Lewis bases, Lewis acids, Brønsted acids and Brønsted bases. However, examples of Lewis acid organocatalysis under homogeneous conditions are comparatively rare. Phosphonium salts are easily accessible and frequently used intermediates in organic synthesis, long known phase‐transfer catalysts and potential Lewis acid organocatalysts. This review covers the application of phosphonium salts as Lewis acidic catalysts for a variety of C C, C O and C N bond‐forming reactions under homogeneous conditions. Moreover, recent developments are included which show the potential of chiral phosphonium salts as asymmetric (phase‐transfer) catalysts. 相似文献
The bulky, but symmetrically beautiful, adamantane ring system is now pervasive throughout physical, medicinal and synthetic chemistry, since it was first discovered in 1924 and coined “dekaterpene”. This fascinating name lived up to its natural product roots when adamantane was isolated from crude oil in 1933, but it was not until 1957 in a landmark contribution by Paul von Ragué Schleyer that adamantane was made readily accessible through synthesis. Beyond the legacy to physical and medicinal chemistry, the adamantane moiety has been quintessential in the development of some of the most important catalysts to date. Considering adamantane's impact on catalyst development past, present and future, this subject is for the first time reviewed herein.
A cationic gold(I)‐catalyzed decarboxylative etherification of propargyl carbonates to selectively produce propargyl ethers is reported. In the reaction the gold(I) catalyst shows a distinct σ‐Lewis acidity rather than the commonly observed π‐Lewis acidity, and thus catalyzes the decarboxylation of a variety of propargyl carbonates to give the corresponding propargyl ethers with high selectivity. This reaction represents a rare example of the tunable reactivity of cationic gold(I) complexes between σ‐Lewis acidity and π‐Lewis acidity.
Room temperature acetalization of aldehydes with methanol has been carried out using metal organic frameworks (MOFs) as solid heterogeneous catalysts. Of the MOFs tested, a copper‐containing MOF [Cu3(BTC)2] (BTC=1,3,5‐benzenetricarboxylate) showed better catalytic activity than an iron‐containing MOF [Fe(BTC)] and an aluminium containing MOF [Al2(BDC)3] (BDC=1,4‐benzenedicarboxylate). The protocol was validated for a series of aromatic and aliphatic aldehydes and used to protect various aldehydes into commercially important acetals in good yields without the need of water removal. In addition, the reusability and heterogeneity of this catalytic system was demonstrated. The structural stability of MOF was further studied by characterization with powder X‐ray diffraction, Brunauer–Emmett–Teller surface area measurements and Fourier‐transformed infrared spectroscopic analysis of a deactivated catalyst used to convert a large amount of benzaldehyde. The performance of copper MOF as acetalization catalyst compares favourably with those of other conventional homogeneous and heterogeneous catalysts such as zinc chloride, zeolite and clay. 相似文献
An efficient synthesis of (E)‐5‐aryl(halo)methylenebicyclo[2.2.2]oct‐2‐enes is reported. Lewis acid‐promoted carbohalogenation of 4‐(3‐arylprop‐2‐ynyl)‐cyclohex‐2‐enols in dichloromethane proceeds rapidly to afford the exo‐methylene‐bridged bicycles in good yields. This method also provides an easy access to (E)‐5‐aryl(halo)methylenebicyclo[2.2.1]hept‐2‐enes from the five‐membered ring 2,6‐enynols. The reactions are procedurally simple and high yielding, producing the aryl(halo)methylene‐bridged bicycles in minutes under air and mild conditions.
The Lewis base‐organocatalyzed asymmetric hydrosilylation of α‐acetamido‐β‐enamino esters was investigated. Among various chiral Lewis base catalysts, a novel catalyst derived from L ‐serine was found to be the most efficient one which can promote the reaction to afford a series of α,β‐diamino acid derivatives with high yields (up to 99%), excellent enantioselectivities (up to 98% ee) and moderate diastereoselectivities (up to 80:20 dr). The absolute configuration of one of the products was determined by the X‐ray crystallographic analysis. In addition, the mechanism and the transition state of the reaction were proposed. 相似文献
Lewis acids catalyze the addition of β‐enaminoacrylates or β‐enaminones to α,β‐unsaturated aldehydes leading to substituted dihydropyridines in high yields under mild reaction conditions. 相似文献
A new approach for the synthesis of homoallylic alcohols and amines directly from alcohols via one‐pot sequential oxidation–Barbier reaction and oxidation–condensation–Barbier reactions, respectively, is reported. The protocol involves the one‐pot ferric chloride‐catalyzed oxidation of alcohols to the corresponding aldehydes with chloramine‐T followed by indium‐mediated Barbier allylation with allyl bromide to afford homoallylic alcohols in 70–90% overall yields. The ferric chloride‐catalyzed condensation of aldehydes and oxidation by‐product p‐toluenesulfonamide followed by indium‐mediated Barbier‐type allylation of the resulting aldimines with allyl bromide affords homoallylic amines in 60–80% overall yields in the same reaction vessel. The present work demonstrates a new one‐pot approach toward homoallylic alcohol and amine synthesis directly from alcohols. 相似文献
Simple ortho‐alkylated anilines have been shown to be excellent iminium catalysts for the epoxidation reaction of α‐substituted acroleins. A range of different α‐substituted acroleins give the epoxide products in good to excellent yields and good chemoselectivity. 相似文献
Asymmetric aldol reactions in aqueous media have been realized by using zinc‐based chiral Lewis acids. The aldol products have been obtained with high yield, diastereocontrol and a good level of enantioselectivity. The reactivity of both acetophenone and propiophenone enol ether surrogates was tested with a range of aldehydes. 相似文献
The oligomerization of n‐butenes in a two‐phase catalyst system consisting of a Lewis acidic ionic liquid (IL) and a nonpolar phase is described. A highly active catalyst system with NiCl2(PMe3)2 was investigated, resulting in 91 % dimers with N‐methylpyrrole as a buffer. The reaction was found to be dependent on the molar ratio of the IL to the catalyst. Additionally, the influence of the Lewis acid was investigated and AlCl3 was determined as the most suitable for activating the nickel complex. The concentration of AlCl3 played an important role in achieving high catalyst activity and dimer selectivity. Several reactions with different pyrrole derivatives demonstrated that the use of a buffer with low steric hindrance was also important with regard to increased dimer selectivity. 相似文献
The first general, highly enantioselective hydrosilylation of benzoxazinones and quinoxalinones has been developed. The chiral Lewis base organocatalysts that are readily accessible from (1S,2R)‐ephedrine and (1R,2S)‐ephedrine promoted the title reaction to afford various chiral dihydrobenzoxazinones and dihydroquinoxalinones with good yields as well as good enantioselectivities. 相似文献