Current Organic Chemistry - Volume 12, Issue 1, 2008

Organophosphorus chemistry continues to be a highly important sector of organic chemistry, as shown by the numerous publications in this field. The 17th International Conference on Phosphorus Chemistry held in Xiamen (China) recently (http://icpc2007.xmu.edu.cn/) highlighted some of the most significant and exciting trends. The importance of this field is also acknowledged by the management of Current Organic Chemistry by encouraging me to put together the 3rd Organophosphorus Special Issue that, like the previous two special issues, summarizes recent results of some selected hot topics. The 10 articles are accommodated in two parts. This series of publications starts with organophosphorus supramolecular chemistry, for which state-of-the-art progress in design and application is presented for host molecules bearing phosphate, phosphonate, phosphinate or phosphine oxide entities. The P-heterocyclic field is represented by a paper on the synthesis and conformation of 1,3,2-dioxa-, 1,3,2-oxaza-, and 1,3,2-diazaphosphorine 2-chalcogenides. This topic is also relevant from the point of view of potential biological activity, an aspect that is more directly involved in the next two articles. The first of these discusses the possible reactivation of RBC cholinesterases inhibited by paraoxon derivatives, while the other gives an overview on the synthesis of ω-phosphinyl-α-amino acids and their potential role as therapeutic agents. Remaining with tetracoordinated P-compounds, the chemistry of azidoalkyl-phosphonates, -phosphinates and -phosphine oxides, as well as the phosphorylation of α-haloimines and that of thiophenes is discussed. In the next section, the use of Wittig- and aza-Wittig reactions in the synthesis of heterocycles and the synthesis and utilization of stabilized phosphorus ylides generated from triphenylphosphine and dialkyl acetylenedicarboxylate are summarized. Finally, antiaromaticity, a newly discovered phenomenon within the framework of organophosphorus chemistry, is explored. The 3. Organophosphorus Special Issue has been divided into two parts published back to back. The five reviews included in this issue (Part II) have been preceeded by five other articles in Volume 11 (Part I). The previous papers are the following: Organophosphorus Supramolecular Chemistry. Part 2. Organophosphorus Receptors by Piotr Mlynarz, Ewa Rudzinska, Lukasz Berlicki and Pawel Kafarski 6-Membered P-Heterocycles: Ring-Condensed 1,3,2-Diheterophosphorine 2-Chalcogenides by Eva Frank and Janos Wolfling Comparison of the Ability of Pyridinium Aldoximes to Reactivate Human RBC Cholinesterases Inhibited by Ethyland Methyl-Paraoxon by Georg Petroianu and Huba Kalasz ω-Phosphinyl-α-amino Acids: Synthesis, and Development Towards Use as Therapeutic Agents by Nick J. Wardle, S. W. Annie Bligh and Harry R. Hudson Synthesis and Reactivity of Azidoalkyl-Phosphonates, -Phosphinates and -Phosphine Oxides by Anna Gajda and Tadeusz Gajda

The chemoselectivity of reactions between α-haloimines - compounds containing a Hal-C-C=N-skeleton - and nucleophilic phosphorus derivatives are discussed systematically. The synthetic potentialities, as well as possible mechanistic pathways of this currently developing field of organophosphorus chemistry are considered. Phosphorylation of the α-haloimines leads mainly to C- or N-phosphorylated compounds as the final products, the selectivity being dependent on the type of halogen, substituents at the imine carbon and nitrogen atoms, and on the nature of phosphorus reagent. The main factors controlling regio- and stereoselectivity are elucidated. A series of novel theoretically and preparatively important transformations have also been illustrated; i.e., new diad rearrangements involving the N→C and C→N transfer of a sulfonyl or a phosphoryl group, the unusual acylation of the electrophilic imine carbon atom by tervalent phosphorus isocyanates, and others. Variety of transformations is connected with the possible participation of C=N bond, halogen atoms or N-substituents, in reactions involving the Hal-C-C=N- arrangement. The use of haloimines as versatile building blocks for synthesis of practically promising functionalized aminophosphonates, bisphosphonates, and phosphorus analogs of dehydro aminoacids, etc., is demonstrated.

This review deals with synthetic methods, chemical transformations, and some physical properties of thienyland benzothienyl substituted phosphorus compounds bearing P-Het or P-CH2-Het bonds. The basic synthetic approaches to these compounds include reactions of metalated thiophenes with phosphorus(III) and (V) halides, phosphorylation of thiophenes in the presence of a mild Lewis acid, use of halogenothiophenes in the Arbuzov reaction, and phosphorylation of thiophenes with phosphorus(III) halides in basic medium. Synthetic approaches to condensed heterocyclic systems of novel types are also considered. Investigation of chemical properties of phosphorylated thiophenes has revealed that, despite the great similarity with phenyl analogues, differences connected to the nature of the heterocycle are observed. The tertiary phosphines bearing at least one thienyl substituent are less active in quaternization and oxidation reactions. At the same time, basic hydrolysis leading to C-P bond cleavage is facilitated, as compared to benzene derivatives.

Applications of Wittig and aza-Wittig reactions in various cyclizations reported during the past ten years are reviewed. The relevant literature is classified into two categories according to these two main approaches and, in both sections, the chemistry is exemplified according to the ring types synthesized. The chemical examples include both intramolecular ring closures and multistep procedures. Within the aza-Wittig reactions, special attention is paid to those products that can undergo electrocyclization to yield nitrogen heterocycles (e.g. pyridines or pyrimidines). In most interesting cases, the reaction mechanism of the transformations is discussed.

Stabilized phosphorus ylides, versatile intermediates in synthetic organic chemistry can be prepared by the novel reaction of dialkyl acetylenedicarboxylates (DAAD), triphenylphosphine (TPP) and acids such as phenols, imides, amides, enols, oximes and alcohols. The reaction involves an intermediate formed by the 1:1 conjugate addition reaction of the TPP to DAAD and concomitant protonation of the intermediate by an acid leads to vinyltriphenylphosphonium salts. The salts are unstable intermediates and converted to stabilized phosphorus ylides via Michael addition reaction. The stabilized phosphorus ylides are able to take part in the normal intramolecular Wittig reactions but they are not generally able to participate in the normal intermolecular Wittig reactions. The intermolecular Wittig reactions of the ylides are observed only with highly electron-poor carbonyl groups such as indane-1,2,3-trione. The ylides are converted to electron-poor alkenes via elimination of TPP in solvent-free conditions. Almost all of the final products are valuable families of compounds.

The organophosphorus chemistry became the one of the most rapidly developing and very important subdiscipline in the organic and organometallic chemistry. This development is providing exciting chemical structures, efficient metal ligands and biologically important pharmacophores. In the present review we first collected and discussed the fourmembered antiaromatic organic and inorganic compounds, containing phosphorous atom in their ring, which were considered and prepared during the past half a century.