Chiral sulfoxides are an important class of compounds that find increasing use as chiral auxiliaries in asymmetric synthesis. [1,2] Current interest also reflects the existence of products with biological properties containing a sulfinyl group with a defined configuration. [3] Several methods for the asymmetric oxidation of prochiral sulfides have been reported, including the use of chiral oxidants, such as chiral oxaziridines, [4] chiral hydroperoxides, [5] and enzymes. [6,7] The majority of investigations have concentrated on the use of chiral metal complexes [1,3,[8][9][10][11] following the initial reports by Kagan and co-workers [12,13] and Modena and co-workers [14] on the use of variously modified Sharpless reagents for this reaction.One of the most widely studied metal-based systems has been that discovered by Bolm and Bienewald, [15,16] who employed a combination of Schiff bases 1 derived from chiral amino alcohols and [VO(acac) 2 ] (1.0 mol %; acac = acetylacetanoate), with aqueous hydrogen peroxide as the oxidant, in a two-phase system using dichloromethane as the solvent at 20 8C (Scheme 1). The advantages of the system developed by Bolm et al. include high activity, the very simple reaction conditions, and the use of hydrogen peroxide as the oxidant. The only drawback associated with the initial ligands tested was that the levels of enantiomeric excess were good, rather than excellent. Other research groups sought to optimize the system, by variation of the aromatic aldehyde, [17][18][19] the amino alcohol, [20] and the manner of addition of hydrogen peroxide, [21] and in many cases it is striking that the best outcome was usually obtained when the reaction was conducted in dichloromethane at 0 8C. A very nice application of the system developed by Bolm et al. was the asymmetric oxidation of ditert-butyl disulfide, reported by Ellman and co-workers, [22] who have since reported the results of spectroscopic studies with a view to understanding the nature of the active catalytic species better.[23] The nature of the active species is still not completely established, but while spectroscopic studies indicate the presence of a vanadium(v)oxomonoperoxo species, [24] recent calculations suggest that the active species may be a vanadium(v)oxohydroperoxide. [25] Recently, the use of analogous salan ligands has been reported to give high levels of enantioselectivity (95 % ee) in the oxidation of methyl phenyl sulfide, but lower levels of enantioselectivity were observed with other substrates. [26] Anson and co-workers screened a variety of chiral Schiff base ligands, and found that the 3,5-diiodo ligand (S)-2, in combination with [VO(acac) 2 ] gave excellent results in the catalytic asymmetric sulfoxidation of alkyl aryl sulfides with hydrogen peroxide, again in dichloromethane at 0 8C.[27] For example, methyl phenyl sulfide was oxidized to (S)-methyl phenyl sulfoxide (81 %, 90 % ee). Recently, Bolm and coworkers reported that a combination of this ligand with iron is also very effective for the asymmetric ox...

Patterns of communication: Reinitzer's discovery of liquid crystals in 1888 was followed by 30 years of scholarly dispute. One hundred years later, Pierre‐Gilles de Gennes was awarded the Nobel Prize in Physics for his contribution to this scientific revolution. The commercial success of liquid crystals was achieved in display applications. Today more than 4 billion people use them in mobile communication devices. Painting: Detail from Raphael's School of Athens fresco.

An efficient two-step synthesis of pyrazoline ligand is described which is an effective "turn on" fluorescent sensor for Cd(2+) in MeCN. Oxidation to the corresponding pyrazole ligand creates a "turn on" fluorescent sensor now selective for Zn(2+) and able to distinguish it from Cd(2+).

Asymmetric oxyallylation reactions and ring-closing metathesis have been used to synthesize compound 3, a key advanced intermediate used in the total synthesis of eleutherobin reported by Danishefsky and co-workers. The aldehyde 6, which is readily prepared from commercially available R-(-)-carvone in six steps in 30 % overall yield on multigram quantities, was converted into the diene 5 utilizing two stereoselective titanium-mediated Hafner-Duthaler oxyallylation reactions. The reactions gave the desired products (8 and 12) in high yields (73 and 83 %, respectively) as single diastereoisomers, with the allylic alcohol already protected as the p-methoxyphenyl (PMP) ether, which previous work has demonstrated actually aids ring-closing metathesis compared to other protective groups and the corresponding free alcohol. Cyclization under forcing conditions, using Grubbs' second-generation catalyst 13, gave the ten-membered carbocycle (E)-14 in 64 % yield. This result is in sharp contrast to similar, but less functionalized, dienes, which have all undergone cyclization to give the Z stereoisomers exclusively. A detailed investigation of this unusual cyclization stereochemistry by computational methods has shown that the E isomer of the ten-membered carbocycle is indeed less thermodynamically stable than the corresponding Z isomer. In fact, the selectivity is believed to be due to the dense functionality around the ruthenacyclobutane intermediate that favors the trans-ruthenacycle, which ultimately leads to the less stable E isomer of the ten-membered carbocycle under kinetic control. During the final synthetic manipulations the double bond of enedione (E)-16 isomerized to the more thermodynamically stable enedione (Z)-4, giving access to the advanced key-intermediate 3, which was spectroscopically and analytically identical to the data reported by Danishefsky and co-workers, and thereby completing the formal synthesis of eleutherobin.