PREFACE [Hot topic: Asymmetric Synthesis (Guest Editor: Tomas Hudlicky)]

It is indeed a pleasure for me to begin the third term as a guest editor for Current Organic Chemistry: Asymmetric Synthesis. Volume 7 of the series provides four contributions concerned with stereoselective and enantioselective synthesis. Two of the chapters address synthetic methodology, while the other two focus on catalysis. Professor Rainer Mahrwald of the Institute for Chemistry at the Humboldt University of Berlin contributed the first chapter of this volume. The aldol-Tishchenko reaction, which involves the aldol reaction of two aldehydes and the subsequent reduction to a monoester of a 1,3-diol, is reviewed with an eye on applications in stereodefined synthesis. It is related, through mechanistic overlap, to the Canizzarro reaction. The chapter flows well from the introduction and description of the classic Tishchenko reaction - formation of an ester from two aldehydes - to more complex applications. In the closing part of the chapter the aldol-Tishchenko reaction of ketones and aldehydes is reviewed in the context of diastereo- and enantioselective synthesis. It is this methodology that has the potential of creating three contiguous and well-differentiated chiral centers. The chapter provides a detailed discussion of mechanisms and gives examples of concise preparation of synthons of the type that are contained in various polyketide-derived natural products. This is an excellent contribution especially in view of the fact that the Tishchenko reaction and its analogues are likely not in the daily repertoire of most synthetic chemists. The review contains 83 references to the primary literature in this field. The second chapter was written by Professor P.J. Persichini III, of Allegheny College, Pennsylvania, and provides an overview of the last ∼40 years in the area of boron mediated transfer reactions as means of C-C bond formation. The chapter is organized according to the distance of the boron complex from the reactive center, i.e., 1,2-transfer, 1,3-transfers, etc., through 1,6-transfers of the functional group. Each section is further organized according to the hybridization of the recipient atom. Mechanistic rationale and the synthetic utility are emphasized by providing examples and applications from natural product syntheses. The chapter is a welcome addition to the literature covering synthetically useful methodologies derived from boron chemistry. The literature coverage contains 82 references, some of which contain multiple citations. Following the two reviews describing modern aspects of synthetic methodology are two reviews dealing with aspects of catalysis. The third chapter is provided by Dr. Andrei V. Malkov and Professor Pavel Kocovsky of the University of Glasgow. It systematically reviews the synthesis and applications of chiral bipyridines to catalytic enantioselective processes. Structure and chirality of such compounds are discussed first according to the symmetry groups and the type of chirality. This part of the review is eminently useful to those chemists not familiar in detail with the field. Next, methods of synthesis are provided for a variety of bipyridine-containing ligands. In the application section cyclopropanation, allylic oxidation, allylic substitution, reduction of ketones, and allylation are discussed along with numerous synthetically useful examples. The review is equally useful for an organometallic expert as it is for a novice to asymmetric catalysis. It includes 106 multiple citation references. The last contribution to this volume is provided by Professor T.V. RajanBabu, Yuan-Yong Yan, and Seunghoon Shin of The Ohio State University. It discusses catalytic reactions performed in water with hydroxyphosphines and derivatives. The prospects and problems of environmentally benign synthesis performed in water are discussed with a focus on hydroxylated phosphines derived from trehalose, salicin, and mannitol. Several types of reactions that depend on phosphine-type catalysts (hydrogenation, hydrocyanation, hydroformylation, allylation, and hydrovinylation) are normally preformed in organic solvent. The authors provide a chronological account of catalyst development in order to allow these reactions to be performed in water. Comparisons of enantiomeric excess are provided for various solvents and catalyst types. It is clear that significant developments in this area have been achieved and the chapter also offers insights on further optimization and substrate specificity of the water-soluble catalysts. This review contains 29 references, several with multiple citations.