Site creation : Enantioselective artificial metalloenzymes have been created by grafting a new active site onto bovine pancreatic polypeptide through the introduction of an amino acid capable of coordinating a copper(II) ion. This hybrid catalyst gave good enantioselectivities in the Diels–Alder and Michael addition reactions in water (see scheme) and displayed a very high substrate selectivity.
Into my arms : Photochemical cyclization of diarylethenes that have two chiral side arms showed up to 100 % de (see scheme). Introduction of these chiral side arms onto the carbon atoms where ring closure occurs is a general strategy for the highly diastereoselective cyclization of diarylethenes.
Getting a fix : N‐heterocyclic carbenes (NHCs) and NHC–CO2 adducts serve as potent organocatalysts for carbonate synthesis by the addition of a CO2 unit to propargylic alcohols or epoxides under mild and solvent‐free reaction conditions (see scheme). The enhanced Lewis basicity of imidazol‐2‐ylidenes bearing electron‐donating alkyl groups on the nitrogen atoms leads to utilizing CO2 as a nucleophilic fragment in the chemical fixation processes.
Myths of steric hindrance : In contrast with current opinion, energy decomposition analysis shows that the presence of bulky substituents at carbon leads to the release of steric repulsion in the transition state shown in the graphic. It is rather the weakening of the electrostatic attraction, and in particular the loss of attractive orbital interactions, that are responsible for the activation barrier.
Tuning sensing abilities! The affinity of three different [15]crown‐5 ether functionalized polythiophenes for alkali ions has been explored (see figure). Ab initio and DFT quantum mechanical calculations show that the binding energy between neutral conducting polymers and metallic ions, which interact attractively, decreases as the size of the ion increases. Oxidation of these polythiophene derivatives significantly reduces their affinity towards alkali ions, becoming low or even nonexistent.
New class of air‐stable catalysts for lactide polymerisation: Guanidine–pyridine hybrid ligands (picture, left) were used to prepare a series of zinc complexes (e.g., depicted cation [ZnL2(CF3SO3)]+, where L is the quinoline‐containing ligand with R1=R2=R3=R4=Me), in which the ligand binds through two different N‐donor atoms. The zinc complexes show high activity in ring‐opening polymerisation of d,l ‐lactide (right), giving polylactide with molecular masses up to 176 000 g mol?1 and in high yield.
Selecting the ring : tert‐Butyldimethylsilyltriflate (TBSOTf)/NEt3 treatment of alkynyl esters tethered to bicycloalkanones leads to the formation of tricyclic allenoates with total diasteroselectivity at the ring junction. An intramolecular alkynylogous Mukaiyama aldol reaction promoted by a TBSOTf/NEt3 dual activation is involved. This novel methodology was illustrated by a formal total synthesis of (±)‐hamigeran B.
A sensitive magnetic nanoprobe : Hydrogen‐bonding interactions are reflected with great sensitivity in the 1H NMR spectra of a high‐spin multinuclear Fe4II [2×2] grid‐type complex (see scheme) and the measured shifts can be used to evaluate the hydrogen‐bond donating ability. The grid complex also represents a prototype of a very sensitive magnetic nanoreceptor for the detection of very small changes around a magnetic center.
Borenes and boranes : Silylaminoiminoborenes, such as depicted, were isolated after treatment of halogen triels with silylaminofluoroboranes. In addition, novel aryl‐ and silyl‐substituted diaminofluoroboranes were also prepared in order to substantiate this reaction route.
Positive discrimination : Chemo‐ and regioselective palladium‐catalyzed cycloetherification of allendiols, namely β,γ‐ and γ,δ‐allendiols, may occur by judicious choice of palladium‐catalyzed conditions owing to their potential ability to discriminate between both nucleophilic sites (see scheme).
