Christina Moberg

C3 SYMMETRY IN ASYMMETRIC CATALYSIS AND CHIRAL RECOGNITION

Rotational symmetry can be an important factor in the design of highly selective receptors for chiral recognition. This is well known for C2 -symmetric compounds, but the concept can be extended to chiral compounds of higher symmetry such as 1.

Polymer-bound bis(oxazoline) as a chiral catalyst

Abstract A chiral bis(oxazoline) was grafted on ArgoGel and used in the palladium-catalysed substitution of (±)-1,3-diphenyl-2-propenyl acetate with dimethyl malonate. The enantioselectivity was the same as that observed when the analogous monomeric catalyst was used (94–95% e.e.), despite the fact that the C 2 symmetry of the ligand was affected when coupled to the polymer. The polymer-supported catalyst could be recycled several times after removal of precipitated Pd(0). The polymer-bound bis(oxazoline) was also applied in a zinc-catalysed Diels–Alder reaction but lower selectivity and reactivity than the monomer was observed.

C3-symmetric tripodal tetra-amines—preparation from chiral amino alcohols via aziridines

Abstract Enantiopure N -sulfonylaziridines, conveniently obtained from readily available enantiopure amino alcohols, undergo smooth ring opening reactions using ammonia as a nucleophile to yield tripodal tetradentate C 3 -symmetric amines. N -alkylation and subsequent removal of the sulfonyl groups provide access to alkyl-substituted analogs.

ENANTIOSELECTIVE ALLYLIC ALKYLATION USING POLYMER-SUPPORTED PALLADIUM CATALYSTS

Abstract Chiral 2′-(4″,5″-dihydro-2″-oxazolyl)-6′-(1-hydroxyalkyl)pyridines were grafted via ester-linkages directly to cross-linked polystyrene and to polyethyleneglycol-containing resins TentaGel and ArgoGel functionalized with carboxylic acid groups or via spacers containing a carboxylic acid group. The polymeric ligands were used in the palladium-catalyzed substitution of rac-1,3-diphenyl-2-propenyl acetate with dimethyl malonate. The enantioselectivities (up to 80% ee) were similar to those observed employing an analogous monomeric catalyst.

Stereospecific lewis acid catalyzed methanolysis of styrene oxide

Abstract The methanolysis of (R)-styrene oxide catalyzed by SnCl4 has been found to proceed with complete regioselectivity with nucleophilic attack at the benzylic position, and with inversion of configuration at the benzylic carbon as the predominant stereochemical course, affording (S)-2-methoxy-2-phenylethanol (95% ee) in high yield.

Patterned self-assembled beads in silicon channels

A novel technique enabling selective bead trapping in microfluidic devices without the use of physical barriers is presented in this paper. It is a fast, convenient and simple method, involving microcontact printing and self‐assembly, that can be applied to silicon, quartz or plastic substrates. In the first step, channels are etched in the substrate. The surface chemistry of the internal walls of the channels is then modified by microcontact printing. The chip is submerged in a bead slurry where beads self‐assemble based on surface chemistry and immobilize on the internal walls of the channels. Silicon channels (100 νm wide and 50 νm deep) have been covered with monolayers of streptavidin‐, amino‐ and hydroxy‐functionalized microspheres and resulted in good surface coverage of beads on the channel walls. A high‐resolution pattern of lines of self‐assembled streptavidin beads, as narrow as 5 νm, has also been generated on the bottom of a 500 νm wide and 50 νm deep channel. Flow tests were performed in sealed channels with the different immobilized beads to confirm that the immobilized beads could withstand the forces generated by water flowing in the channels. The presented results indicate that single beads can be precisely positioned within microfluidic devices based on self‐assembly which is useful as screening and analysis tools within the field of biochemistry and organic chemistry.

Stereomutation in trigonal-bipyramidal systems: a unified picture.

Same difference: Berry pseutorotation (BPR) and Ugi turnstile rotation, which are generally treated as two distinctly different mechanisms for rearrangement of trigonal-bipyramidal structures, have been shown to be equivalent. Alternative mechanisms consist of sequences of pseudorotations proceeding in a single step.

Palladium(II)-catalyzed oxidation of alcohols with air as reoxidant

Oxidation of primary and secondary aliphatic and secondary benzylic alcohols into their corresponding aldehydes and ketones was achieved in good yields with palladium catalysts using air as the reo ...

Mechanism of Diphenylprolinol Silyl Ether Catalyzed Michael Addition Revisited but Still Controversial

Mechanism of Diphenylprolinol Silyl Ether Catalyzed Michael Addition Revisited but Still Controversial

Self-assembled and self-sorted array of chemically active beads for analytical and biochemical screening

A technique for generating a general screening platform consisting of dots of immobilized beads on silicon has been developed via self-sorting and -assembly of different kinds of beads. The dots are defined by a teflon-like film, which due to its hydrophobic characteristics also prevents cross-contamination of liquid from different dots. To enable functionalization of individual dots with different target molecules simultaneously a new way of microcontact printing has been explored where different target solutions are printed in parallel using one stamp. In order to show that this platform can be designed for both biochemical assays and organic chemistry, streptavidin-, amino- and hydroxy-functionalized beads have been self-sorted and -assembled both on separate and common platforms. The self-sorting and -arrangement are based on surface chemistry only, which has not previously been reported. Beads of different sizes and material have successfully been immobilized in line patterns as narrow as 5 mum. Besides silicon, quartz and polyethylene have also been used as substrates.