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In an attempt to develop new dopants for improved ferroelectric properties in liquid crystals, aryloxazolines have been chosen as chiral moieties. They were prepared in optically active form from (S)-p-amino alcohols via a short stereospecific synthesis and incorporated into mesogenic systems. Mesogenic and ferroelectric properties of 11 compounds in five series of chiral oxazoline derivatives [I(OH), I(H), II(OH), II(H), and III(OH)] have been studied. In order to establish the relationship between the molecular structure and ferroelectric properties, an indepth structural investigation of both H-bonded and non-H-bonded phenyloxazoline moieties was carried out (by means of semiempirical calculations-AM1-and spectroscopic studies-IR, UV and 'H NMR). These studies have proved a planar structure for both types of structures, which should have a strong influence on ferroelectric properties. These properties have been evaluated in 10 mol % binary mixtures. The highest Ps values were measured for compounds of series I(OH) [P, maxI(OH)a = 16.7 nC/cm2, P, maxI(OH)b = 13.2 nC/cm2] containing a hydrogen bond, which makes the chiral part of the molecule more rigid. Compound III(0H)a shows a wide SmC* phase range which supercools well below room temperature, and it has been studied as a ferroelectric liquid crystal in the pure state. The P, max measured is appreciably high: 225 nC/cm2. Its special thermal behavior (showing a glass transition at -28 "C) makes this compound very interesting from the point of view of practical applications and will be the target of further studies.

Abstract:The first example of an enantioselective and diastereoselective catalytic nitro-Mannich reaction using a second-generation heterobimetallic complex has been developed. The corresponding nitro-Mannich products were obtained in up to 83% ee with a dr up to 7:1.Key words: 1,2-diamines, asymmetric catalysis, imines, nitro compounds, nucleophilic additionsThe nitro-Mannich reaction, the nucleophilic addition of nitroalkanes to imines, gives rise to b-nitroamines and the nitro group can be converted easily into the amino function providing the useful vicinal diamines.1 Although the first example of this class of reaction appeared in 1896, 2 until recent reports by Anderson et al. 3 no stereoselective version of the nitro-Mannich reaction had been known. A general enantioselective catalytic version of this reaction should be a powerful tool for the preparation of chiral vicinal diamines. In 1999 we reported about the enantioselective catalytic nitro-Mannich reaction, 4 and although this was the first example of an enantioselective nitro-Mannich reaction, the reaction suffered from the limitation that only nitromethane could be used as nucleophile. In the case of a nitroalkane with a longer carbon chain than nitromethane, the reaction forms two stereocenters and diastereoselectivity as well as enantioselectivity becomes a matter of concern. If this addition could be achieved both in an enantioselective and diastereoselective manner, this reaction would be much more powerful and useful. Herein, we wish to report the first example of an enantioselective and diastereoselective catalytic nitro-Mannich reaction. Although our former catalyst YbKH 2 [(R)-binaphthoxide] 3(1) gave the product in 79% yield and 91% ee in the case of benzaldehyde imine 2a and nitromethane, 4 catalyst 1 did not promote the reaction of 2a and nitroethane (3a) at all. We thought that the binding pocket of catalyst 1 might be too small both for the N-phosphinoyl imine and nitroethane, and that a catalyst having a larger binding pocket for substrates might be more suitable for this reaction. AlLi[(R)-binaphthoxide] 2 complex, (R)-ALB 5 is a heterobimetallic asymmetric complex containing both Brønsted basic and Lewis acidic functionalities. 6 Having two binaphthoxide moieties as chiral ligands (R)-ALB might have a larger binding pocket for the substrates compared to catalyst 1 with three binaphthoxide units. Although (R)-ALB itself did not promote the reaction of 2a and 3a at lower temperature, 7 we were pleased to find that the complex of ALB (20 mol %) and KO-t-Bu (18 mol %), socalled second-generation ALB, 8 catalyzed the reaction at -40°C in THF giving rise to 4a after 48 h in 71% yield, a dr (anti:syn) of 3:1 and an ee of 35% for the major diastereomer. Changing the solvent from THF to toluene 4a was obtained in 83% yield and 51% ee, but, unfortunately, the dr decreased to 2:1. The best result was achieved when dichloromethane was used as a solvent. Thus, the nitroMannich reaction of 2a and 3a gave 4a after 48 h in 77% yield and a dr o...

The synthesis of pseudopeptides with a chiral alpha-sulfonimidoylcarboxy moiety in the backbone is described. Starting from readily available (Ss)-S-methyl S-phenyl sulfoximine and various cyclic and acyclic alpha-amino acids the desired products are obtained in good yields with peptide coupling methodology. Specific secondary structures caused by intramolecular hydrogen bonds may be adopted. Results of NMR studies to reveal conformational preferences will be discussed.

As the title states, this book describes the chemistry of inhibitors, chemical species that reduce the rate of certain chemical reactions or that prevent or delay the oxidative decomposition of organic compounds and materials. In the latter case, the "inhibitor" is more commonly referred to as an antioxidant. In the instances discussed, the mechanism of inhibition involves intercepting a reactive free radical intermediate, and thus, the text also provides an overview of free radical chain processes.The text has three parts. The first deals with "straight chain reactions", characterized by elementary steps that consume and produce a reactive free radical (propagation steps) to sustain the chain process. This section discusses the general kinetic characteristics of such processes, including the effect of inhibitors on rate, and treats a number of important topics, including free radical polymerization and the oxidation of hydrocarbons. In addition, important classes of inhibitors (antioxidants), such as phenols and aromatic amines, are discussed separately in considerable detail. The second part of the book covers degenerate chain branching reactions. These are reactions in which the initially formed products provide new pathways for the production of free radicals. This section deals mostly with autoxidation of organic compounds and materials and the chemistry of hydroperoxides (ROOH) and peroxyl radicals (ROO • ). The last section of the book deals with branching chain processes, which are characterized by elementary steps that generate more radicals than they consume. Accordingly, this section considers the effect of inhibitors on ignition, combustion, and explosion.The reactions are discussed in terms of their kinetics and, to a somewhat lesser extent, their thermodynamics. Many of the reactions of inhibitors with radicals involve atom transfer, typically hydrogen atom transfer. There is an excellent presentation and application of a theory that expresses the activation energy as a function of the bond strengths of the pertinent chemical species, triplet repulsion in the transition state, etc., enabling the reader to achieve a good appreciation of the factors that govern the rate of these reactions. The text, however, does not go into great detail describing the molecular basis for radical reactivity, structural effects, applications of MO theory, etc. and should not be viewed as a comprehensive treatise on free radical chemistry. To get the most out of the text, the reader will need to be fairly comfortable with chemical kinetics, as most of the reaction mechanisms are discussed in terms of moderately complicated rate equations.The book is translated from Russian but does not read like a translation, in that the text flows smoothly and is free of grammatical errors. The material is certainly up-to-date, but most of the references predate 1990, partly reflecting the maturity of the field. There are some modern topics discussed, including the effect of hydrogen bonding on the reactivity of phenols as radical tr...