Microwave-assisted synthesis of functionalized flavones and chromones

A facile microwave synthesis of functionalized flavones and chromones via the cyclization of 1-(2-hydroxyaryl)-3-aryl-1,3-propanedione is described.     

Efficient total synthesis of (+)-curcuphenol via asymmetric organocatalysis

The catalytic enantioselective synthesis of (+)-curcuphenol is described herein. This approach involves the use of an organocatalytic alkylation of m-anisidine, a diazotation/Sandmeyer reaction of the amine and a Negishi-type coupling with dimethylzinc. This versatile strategy allows for the rapid synthesis of other members of this class of natural products.     

Synthesis of substituted imidazoles via organocatalysis

A one-pot synthesis of substituted imidazoles is described. The cornerstone of this methodology involves the thiazolium-catalyzed addition of an aldehyde to an acyl imine to generate the corresponding alpha-ketoamide in situ followed by ring closure to the imidazole in a one-pot sequence. The extension of this methodology to the one-pot synthesis of substituted oxazoles and thiazoles is also described. [reaction: see text]     

Recent advances in asymmetric fluorination and fluoroalkylation reactions via organocatalysis

The past decade has witnessed the significant advances of asymmetric organocatalytic fluorination, monofluoroalkylation, gem-difluoroalkylation, and trifluoromethylation. This digest summarizes the latest progress of these reactions. In the research area of asymmetric organocatalytic fluorination, a new catalysis concept, chiral anion phase-transfer catalysis strategy, has emerged and has proved to be highly efficient. Asymmetric organocatalytic monofluoroalkylation and gem-difluoroalkylation have been much less explored and the Lewis base/acid catalysis has been the most used strategy. Compared with electrophilic trifluoromethylation, nucleophilic trifluoromethylation has been intensively studied in the research field of asymmetric organocatalytic trifluoromethylation.     

Synthesis of aromatic aldehydes by organocatalytic [4+2] and [3+3] cycloaddition of α,β-unsaturated aldehydes

Organocatalytic inter- and intramolecular [4+2] and [3+3] cycloadditions of α,β-unsaturated aldehydes to give polysubstituted aromatic aldehydes are described. High periselectivity for the cycloadditions, with catalyst effects exerted by l-proline and pyrrolidine-HOAc, as well as cocatalyst, additive effects, has been observed.     

Asymmetric organocatalysis of epoxidation by iminium salts under non-aqueous conditions

Three iminium salts have been tested as catalysts for the asymmetric epoxidation of simple alkenes under non-aqueous conditions in various solvents, at varying temperatures, employing tetraphenylphosphonium monoperoxybisulfate (TPPP) as the stoichiometric oxidant. Enantiomeric excesses of up to 89% have been observed.     

NH-Isoxazolo-bicycles; new molecular scaffolds for organocatalysis

A new scaffold for organocatalysis of the Diels-Alder reaction is disclosed; an isoxazolidine ring forms the core of the catalyst and its activity is enhanced by judicious fusion of a second five-membered heterocycle to the c-edge. The catalyst performance is improved by the incorporation of an endo-cyclic electron withdrawing group adjacent to the fusion point. The organic core is effective only in the presence of an acid co-catalyst and whilst the two-component system shows potential as an enantioselective catalyst it is demonstrated that stereocontrol is a feature of the organic core and is fully independent of the choice of co-catalyst.     

Photoswitchable organocatalysis in acylation of alcohol using dithienylethene-linked azoles

Three novel dithienylethenes bearing azole derivatives were synthesized and found to undergo reversible photocyclization of the dithienylethene units upon alternate irradiation with UV and visible light. Among them, the dithienylethene-linked imidazole and N-phenylimidazole exhibited a relatively high organocatalytic activity for the acylation of 2-decanol with acetic anhydride, and the catalytic activity of the dithienylethene-linked imidazole could be switched by reversible photoinduced cyclization/cycloreversion of the dithienylethene unit.     

Efficient organocatalysis with a calix[4]pyrrole derivative

The 10α,20β-bis(4-nitrophenyl)-calix[4]pyrrole was found to act as an effective organocatalyst for the hetero Diels-Alder reaction of Danishefsky’s diene with aromatic aldehydes. This discovery is the first reported case of a calixpyrrole that exhibits organocatalytic activity.     

Expedient synthesis of xanthones and multi-functionalized chromones from 1,1-diacyl cyclopropanes

We report the rapid synthesis of various cycloheptane-fused chromones and an oxepine fused flavone in 5 steps from the corresponding 2-hydroxy acetophenone. Furthermore, we describe the synthesis of xanthones, in moderate to good yield, from 2,3-disubstituted flavones using a Friedel Crafts alkylation strategy.     

Efficient total synthesis of (+)-exo-, (−)-endo-brevicomin and their derivatives via asymmetric organocatalysis and olefin cross-metathesis

The catalytic enantioselective synthesis of (+)-exo-, (−)-endo-brevicomin and their derivatives is described herein. This approach involves the use of the organocatalyzed asymmetric α-aminoxylation of aldehyde, in situ indium mediate allyation and olefin cross-metathesis. This versatile strategy allows for the rapid synthesis of other members of this class of natural products.     

Synthesis of chromones

A general procedure for the preparation of chromones from the boron difluoride complex of o-hydroxyaryl methyl ketones is described. One of the best methods used for the preparation of chromones and benzochromones is the treatment of o-hydroxyaryl methyl ketones with the dimethylacetal of dimethylformamide followed by treatment with sulfuric acid (1). We previously had shown (2) that benzochromone 4 was prepared in reasonable yield by the following reaction sequence.     

高对映选择性有机催化的七元环状亚胺二苯并1,4-氧氮杂卓和丙酮的直接Mannich反应(英文)

用脯氨酸作为催化剂,研究了各种取代的二苯并1,4-氧氮杂卓衍生物类七元环状亚胺和丙酮的直接Mannich反应,该反应能高对映选择得到一系列旋光活性的含有β羰基的七元环状氮杂环化合物(93%–98%ee).用丁酮作为Mannich给体时,能得到专一的区域选择性和96%–97%ee的产物.进一步通过X射线单晶衍射分析其中一个产物的衍生物,确定了产物手性中心绝对构型为R,其它同类型产物绝对构型随后通过化学类比方法推断确认.     

Synthesis of functionalized organotrifluoroborates via halomethyltrifluoroborates

[reaction: see text] Potassium bromo- and iodomethyltrifluoroborates have been prepared via in situ reaction of n-BuLi with dibromo- and diiodomethane, respectively, in the presence of trialkyl borates, followed by treatment with KHF(2). Moreover, a new synthetic method for the preparation of potassium organotrifluoroborates through nucleophilic substitution of the halide in these potassium halomethyltrifluoroborates is described.     

An organocatalytic route to the synthesis of lactone moiety of compactin and mevinolin

An efficient synthesis of lactone moiety of compactin has been achieved. The stereogenic centers were generated by means of iterative proline-catalyzed sequential α-aminoxylation and Horner-Wadsworth-Emmons (HWE) olefination of aldehydes.     

Synthesis of atropoisomeric pyridines via cobalt-catalyzed cocyclotrimerization of diynes with benzonitrile

Arylpyridines (precursors for potential organocatalysts) are easily accesible by cobalt-catalyzed cocyclotrimerization of ortho-substituted 1-aryl-1,7-octadiynes with benzonitrile. The scope of the reaction with respect to the ortho substituents (OMe, Me, COOMe, NHCOMe, F, etc.) was investigated. Three potentially atropoisomeric arylpyridines were prepared and one of them was converted into the corresponding N-oxide and resolved into its enantiomers. The absolute configuration of the N-oxide was established by X-ray crystal structure analysis. Preliminary results of its application in asymmetric organocatalysis are presented.     

Seebach’s oxazolidinone is a good catalyst for aldol reactions

Seebach’s proline-derived oxazolidinone 2d overcomes (S)-proline and is at least as efficient as (S)-5-(pyrrolidin-2-yl)tetrazole in several organocatalytic aldol reactions examined. A quick exchange takes place between 2d and carbonyl compounds that gives new bicyclic oxazolidinones, in equilibrium with the very minor active species (enamines). Maximum yields of the aldols (β-hydroxy ketones) were achieved after 1-4 h when, with proline, they are attained after 30-48 h.     

Synthesis of functionalized bisphosphonates via click chemistry

An efficient general synthetic approach giving the possibility for facile, rapid and cheap access to a wide range of novel nitrogen-bisphosphonates (N-BPs) as potent drug candidates, based on the reaction of mono- and bis-propargyl-substituted bisphosphonates with a variety of azides under Cu(i) catalysis ("click" methodology), has been developed. The method allows the incorporation of two functionalities into the N-BP molecule simultaneously, as well as to ligate in situ two N-BPs to one another via the one-pot reaction of organic dibromides with propargyl-substituted bisphosphonates, generating both the diazide and Cu(I) moieties.     

Water influences the enantioselectivity in the proline or prolinamide-catalyzed aldol addition of acetone to isatins

The addition of small quantities of water to the proline or prolinamide-catalyzed aldol addition of acetone to isatin can result in increased enantioselectivity. DFT B3LYP calculations with a water molecule explicitly incorporated in the aldol transition states reproduce the observed enantioselectivity.