Chiral Brønsted Acid Directed Iron‐Catalyzed Enantioselective Friedel–Crafts Alkylation of Indoles with β‐Aryl α′‐Hydroxy Enones

A cooperative catalytic system established by the combination of an iron salt and a chiral Brønsted acid has proven to be effective in the asymmetric Friedel–Crafts alkylation of indoles with β‐aryl α′‐hydroxy enones. Good to excellent yields and enatioselectivities were observed for a variety of α′‐hydroxy enones and indoles, particularly for the β‐aryl α′‐hydroxy enones bearing an electron‐withdrawing group at the para position of the phenyl ring (up to 90 % yield and 91 % ee). The proton of the chiral Brønsted acid, the Lewis acid activation site, as well as the inherent basic site for the hydrogen‐bonding interaction of the Brønsted acid are responsible for the high catalytic activities and enantioselectivities of the title reaction. A possible reaction mechanism was proposed. The key catalytic species in the catalytic system, the phosphate salt of Fe^III, which was thought to be responsible for the high activity and good enantioselectivity, was then confirmed by ESIMS studies.     

Cross‐Reactive Sensor Arrays for the Detection of Peptides in Aqueous Solution by Fluorescence Spectroscopy

A simple but powerful method for the sensing of peptides in aqueous solution has been developed. The transition‐metal complexes [PdCl₂(en)], [{RhCl₂Cp*}₂], and [{RuCl₂(p‐cymene)}₂] were combined with six different fluorescent dyes to build a cross‐reactive sensor array. The fluorescence response of the individual sensor units was based on competitive complexation reactions between the peptide analytes and the fluorescent dyes. The collective response of the sensor array in a time‐resolved fashion was used as an input for multivariate analyses. A sensor array comprised of only six metal–dye combinations was able to differentiate ten different dipeptides in buffered aqueous solution at a concentration of 50 μM . Furthermore, the cross‐reactive sensor could be used to obtain information about the identity and the quantity of the pharmacologically interesting dipeptides carnosine and homocarnosine in a complex biological matrix, such as deproteinized human blood serum. The sensor array was also able to sense longer peptides, which was demonstrated by differentiating mixtures of the nonapeptide bradykinin and the decapeptide kallidin.     

A Highly Versatile Catalyst System for the Cross‐Coupling of Aryl Chlorides and Amines

The syntheses of 2‐(di‐tert‐butylphosphino)‐N,N‐dimethylaniline ( L1 , 71 %) and 2‐(di‐1‐adamantylphosphino)‐N,N‐dimethylaniline ( L2 , 74 %), and their application in Buchwald–Hartwig amination, are reported. In combination with [Pd(allyl)Cl]₂ or [Pd(cinnamyl)Cl]₂, these structurally simple and air‐stable P,N ligands enable the cross‐coupling of aryl and heteroaryl chlorides, including those bearing as substituents enolizable ketones, ethers, esters, carboxylic acids, phenols, alcohols, olefins, amides, and halogens, to a diverse range of amine and related substrates that includes primary alkyl‐ and arylamines, cyclic and acyclic secondary amines, N? H imines, hydrazones, lithium amide, and ammonia. In many cases, the reactions can be performed at low catalyst loadings (0.5–0.02 mol % Pd) with excellent functional group tolerance and chemoselectivity. Examples of cross‐coupling reactions involving 1,4‐bromochlorobenzene and iodobenzene are also reported. Under similar conditions, inferior catalytic performance was achieved when using Pd(OAc)₂, PdCl₂, [PdCl₂(cod)] (cod=1,5‐cyclooctadiene), [PdCl₂(MeCN)₂], or [Pd₂(dba)₃] (dba=dibenzylideneacetone) in combination with L1 or L2 , or by use of [Pd(allyl)Cl]₂ or [Pd(cinnamyl)Cl]₂ with variants of L1 and L2 bearing less basic or less sterically demanding substituents on phosphorus or lacking an ortho‐dimethylamino fragment. Given current limitations associated with established ligand classes with regard to maintaining high activity across the diverse possible range of C? N coupling applications, L1 and L2 represent unusually versatile ligand systems for the cross‐coupling of aryl chlorides and amines.     

Preparation of Enzymatically Recyclable Hydrogels Through the Formation of Inclusion Complexes of Amylose in a Vine‐Twining Polymerization

In this paper, we describe the preparation of hydrogels through the formation of an inclusion complex of amylose in a vine‐twining polymerization. This is achieved by the phosphorylase‐catalyzed polymerization of α‐D ‐glucose 1‐phosphate from maltoheptaose primer, in the presence of a water‐soluble copolymer having hydrophobic graft‐chains (poly(acrylic acid sodium salt‐graft‐δ‐valerolactone)). The mixture turns into a gel during the polymerization process. Evaluation of the hydrogels is conducted by shear‐viscosity measurements of the products. For the hydrogels with relatively high viscosities, fast relaxation modes of the cooperative diffusions are observed by scanning microscopic light scattering measurements, which indicate the nanometer‐size network structures of the hydrogels. In addition, we found that the enzymatic disruption and reproduction of the hydrogels are achieved by the combination of the amylase‐catalyzed hydrolysis of the amylose component and the formation of amylose by the phosphorylase‐catalyzed polymerization.     

Asymmetric Catalytic Aziridination of Cyclic Enones

The first catalytic method for the asymmetric aziridination of cyclic enones is described. The presented organocatalytic strategy is based on the use of an easily available organocatalyst that is able to convert a wide range of cyclic enones into the desired aziridines with very high enantiomeric purity and good chemical yield. Such a method may very well open up new opportunities to stereoselectively prepare complex chiral molecules that possess an indane moiety, a framework that is found in a large number of bioactive and pharmaceutically important molecules