Chiral Ligands in Hypervalent Iodine Compounds: Synthesis and Structures of Binaphthyl-Based λ3-Iodanes

Several novel binaphthyl-based chiral hypervalent iodine(III) reagents have been prepared and structurally analysed. Various asymmetric oxidative reactions were applied to evaluate the reactivities and stereoselectivities of those reagents. Moderate to excellent yields were observed; however, very low stereoselectivities were obtained. NMR experiments indicated that these reagents are very easily hydrolysed in either chloroform or DMSO solvents leading to the limited stereoselectivities. It is concluded that the use of chiral ligands is an unsuccessful way to prepare efficient stereoselective iodine(III) reagents.     

Rapid Generation and Safe Use of Carbenes Enabled by a Novel Flow Protocol with In‐line IR spectroscopy

A powerful new continuous process for the formation and use of donor/acceptor‐substituted carbenes is described. The safety profile of diazo group transfer on methyl phenylacetate was determined including kinetic studies in batch and in flow using in‐line IR analysis. Batch work‐up and liquid chromatography were circumvented by developing an optimized liquid/liquid flow separation method providing aryl diazoacetates in high purity. Fast screening of reaction conditions in flow with in‐line IR analysis allowed rapid reaction optimization. Finally, a multistep process of diazo group transfer, extraction, separation and subsequent diazo decomposition combined with multiple X?H insertion reactions was established.     

Short Total Synthesis of Ajoene

We describe a short total synthesis of ajoene, a major biologically active constituent of garlic. The instability of allicin as the only other known alternative starting material has led to the development of a reliable procedure for the synthesis of ajoene from simple building blocks that is also suitable for upscale operations.     

Analyse der Alkohole

Analytical and Bioanalytical Chemistry -     

Hypervalent iodine-mediated aziridination of alkenes: mechanistic insights and requirements for catalysis

By detailed study of the possible side reactions in the previously reported aziridination of alkenes with N-aminoheterocycles mediated by hypervalent iodine reagents, the requirements to make this reaction catalytic in iodoarene have been determined. The reaction requires an oxidant that will oxidise iodoarenes but that does not oxidise alkenes, but it is possible that no such oxidant actually exists! A method in which the hypervalent iodine reagent can be recycled without the need for reisolation is possible. Further study into the mechanism of this reaction gives tentative evidence that the reaction proceeds through formation of an aminoiodane that reacts directly with the alkene, contrary to previous literature reports in which an acetoxyamine intermediate is suggested. The temperature effect of this reaction is remarkable.     

Preparation and characterization of poly(lipid)-coated, fluorophore-doped silica nanoparticles for biolabeling and cellular imaging

The fabrication, characterization, and implementation of poly(lipid)-coated, highly luminescent silica nanoparticles as fluorescent probes for labeling of cultured cells are described. The core of the probe is a sol-gel-derived silica nanoparticle, 65-100 nm in diameter, in which up to several thousand dye molecules are encapsulated (Lian, W.; et al. Anal. Biochem. 2004, 334, 135-144). The core is coated with a membrane composed of bis-sorbylphosphatidylcholine, a synthetic polymerizable lipid that is chemically cross-linked to enhance the environmental and chemical stability of the membrane relative to a fluid lipid membrane. The poly(lipid) coating has two major functions: (i) to reduce nonspecific interactions, based on the inherently biocompatible properties of the phosphorylcholine headgroup, and (ii) to permit functionalization of the particle, by doping the coating with lipids bearing chemically reactive or bioactive headgroups. Both functions are demonstrated: (i) Nonspecific adsorption of dissolved proteins to bare silica nanoparticles and of bare nanoparticles to cultured cells is significantly reduced by application of the poly(lipid) coating. (ii) Functionalization of poly(lipid)-coated nanoparticles with a biotin-conjugated lipid creates a probe that can be used to target both dissolved protein receptors as well as receptors on the membranes of cultured cells. Measurements performed on single nanoparticles bound to planar supported lipid bilayers verify that the emission intensity of these probes is significantly greater than that of single protein molecules labeled with several fluorophores.     

Stereocontrolled Photooxygenations–A Valuable Synthetic Tool§

The stereochemical course of the singlet-oxygen ene reaction with acyclic olefins may be controlled if in the substrate conformational fixation (1,3-allylic strain) an allyl-ic substituent for interaction with the attacking oxygen enophile aligns. Various substrates were chosen to elucidate the features of the olefin that are necessary to control the sense (threo versus erythro) and the extent of the ii-facial preference of the singlet-oxygen attack. Depending on the electronic properties of the double bond and the nature of the allylic substituent, threo or erythro selectivity may be imposed through hydrogen bonding, electrostatic and steric effects and stereoelectronic alignment. Such directing properties, especially that of the hydroxy group, were also confirmed in the other reaction modes of singlet oxygen, namely the [4+2] cycloaddition to chiral naphthylenic alcohols and the [2+2] cycloaddition to an adamantylidene-substituted allylic alcohol. The syntheses of the natural products Merucathin and Iso-dihydromahubanolide B are two examples in which such stereocontrolled photooxygenations have been used as key steps to build up the required chirality diastereose-lectively.     

Die ersten Röntgenstrukturen kationischer Diorganylzinn(IV)‐Dichelate [R2Sn(L–L)2]2⊕ mit zweizähnigen Phosphanoxid‐Liganden: Di(methansulfonyl)amid als nichtkoordinierendes Gegenion

Polysulfonylamines. CXI. The First X‐Ray Structures of Cationic Diorganyltin(IV) Dichelates [R₂Sn(L–L)₂]^2⊕ Involving Bidentate Phosphine Oxide Ligands: Di(methanesulfonyl)amide as a Non‐Coordinating Counter‐Ion The reaction of Me₂Sn(A)₂, where A^⊖ = (MeSO₂)₂N^⊖, with DPPOE = ethane‐1,2‐diylbis(diphenylphosphine oxide) or CDPPOET = cis‐ethene‐1,2‐diylbis(diphenylphosphine oxide) yields the ionic dichelates [Me₂Sn(dppoe)₂]^2⊕ · 2 A^⊖ ( 1 ; monoclinic, space group P2₁/c) and [Me₂Sn(cdppoet)₂]^2⊕ · 2 A^⊖ ( 2 ; monoclinic, P2₁/n). A solvated variety of 2 , [Me₂Sn(cdppoet)₂]^2⊕ · 2 A^⊖ · Et₂O · 0.15 MeCN ( 4 ; triclinic, P 1), was serendipitously obtained by thermal degradation of the new compound [Me₂Sn(A)(μ‐OH)]₂ · 2 CDPPOET in an MeCN/Et₂O medium. The crystals of 1 , 2 and 4 consist of discrete formula units (one independent unit for 1 and 2 , two independent units for 4 ); in the structure of 4 , the solvent molecules are located in lattice cavities. All the tin atoms lie on crystallographic inversion centres and display moderately distorted octahedral C₂O₄ coordinations with short Sn–O bonds in the range 218–223 pm. Within the formula units, the anions are connected to the P–CH donor groups of the chelating ligands by C–H…O/N interactions, some of which are remarkably short (e.g. in 1 : H…O 220 pm, C–H…O 170°; H…N 242 pm, C–H…N 153°).     

Generalised energy conservation law for wave equations with variable propagation speed

We investigate the long time behaviour of the L²-energy of solutions to wave equations with variable speed of propagation. The novelty of the approach is the combination of estimates for higher order derivatives of the coefficient with a stabilisation property.