Band 77, Heft 12

The 7th IUPAC International Conference on Heteroatom Chemistry (ICHAC-7) was held in Shanghai, China, on 21-25 August 2004. This conference was co-organized by Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences (CAS); Chinese Chemical Society; Shanghai Society of Chemistry and Chemical Industry; and State Key Laboratory of Organometallic Chemistry and State Key Laboratory of Elemento-organic Chemistry. Three hundred participants attended the conference, with about 150 attendants from 23 different countries other than China. The scientific program consisted of 8 plenary lectures, 1 keynote lecture, 38 invited lectures, 56 p, and 120 posters. This conference focused on the following 6 major themes: - Organocatalysis - Heteroatom chemistry directed toward organic synthesis - Mechanistic and structural aspect of heteroatom chemistry - New heteroatom-containing materials - Biologically relevant heteroatom chemistry - Supramolecular chemistry of heteroatom. All the lecture sessions were held in Everbright Exhibition Center. The following highlighted lectures are representative of the quality of material presented at the conference: - Robert R. Holmes, University of Massachusetts, "Phosphoryl transfer enzymes and hypervalentphosphorus chemistry" - Christopher A. Reed, University of California at Riverside, "Strongest but gentlest: New acids fororganic and inorganic chemistry" - Xiyan Lu, Shanghai Institute of Organic Chemistry, CAS, "Synthetic methodologies using tertiaryphosphines as nucleophilic catalysts" - Tetsuo Otsubo, Hiroshima University, "Functional oligothiophenes as advanced molecular electronicsmaterials" - Dao-Ben Zhu, Institute of Chemistry, CAS, "Recent advances of molecular material in theOrganic Solid Laboratory, CAS" - Ian Manners, University of Toronto, "Catalytic routes to rings, chains, and macromolecules basedon inorganic elements" - Masaaki Yoshifuji, Tohuku University, "Recent develpments in the chemistry of low-coordinatedorganophosphorus compounds" - Peter Jutzi, University of Bielefeld, "Cyclopentadienyl and ferrocenyl chemistry of some p-blockelements" - Andreas Pfaltz, University of Basel, "Design of heterocyclic ligands for asymmetric catalysis" The organizers also prepared a series of rich social programs for the participants of the conference, which included a welcome party and a city sightseeing tour of Shanghai. ICHAC-7 was a fruitful meeting for all participants, in particular, the young scientists and students who found a world forum to present and discuss their results, meet scientists from other countries, exchange experiences, and socialize with scientists from all fields of heteroatom chemistry. Many of these contacts have led to new cooperation and exchanges among students and young and senior scientists. In addition to the lectures in this issue, six lectures of this conference have been documented in the Chinese Journal of Chemistry , Vol. 23, Nos. 8,9 (2005). The 8th IUPAC International Conference on Heteroatom Chemistry will be held in 2007 in Riverside, CA and will be hosted by Prof. Christopher A. Reed of the University of California at Riverside. Xiaoyu Huang Conference Editor

Allenoates or 2-alkynoates are known to react with tertiary phosphines to form the phosphine-substituted 1,3-dipoles, which can react with various substrates with the simultaneous elimination of the tertiary phosphine. The reaction is catalytic to the tertiary phosphine used. The investigation of the appropriate dipolarophiles and the further extension of this reaction are discussed.

In this perspective article, some of our recent work directed at the development of new catalytic routes to rings, chains, and macromolecules based on main group and transition elements will be discussed.

This article reviews the recent progress of fullerene-tethered oligothiophenes as advanced molecular electronics materials. By covalent linkage with fullerenes, oligothiophenes can be modified into intelligent functional materials. In addition to the characteristics of oligothiophenes as well as fullerenes, these linkage systems show intriguing physical properties such as photoinduced electron transfer, energy transfer, and ambipolar conductivity, caused by interactions between both components. These properties are of great use for the wide applications of the linkage compounds to devices. Their practical uses for photovoltaic cells and field effect transistors are demonstrated.

Sterically protected organophosphorus compounds are described, involving diphosphenes, phosphaethenes, diphosphinidenecyclobutenes (DPCBs), phosphaalkynes, phosphaquinones, diphosphathienoquinones, and so on of coordination number 2 or 1. Application of the DPCBs as well as phosphinophosphaethenes as a ligand of transition-metal catalysts for several organic coupling reactions has been investigated.

Two types of transition-metal-catalyzed cross-coupling reactions, which both lead to the formation of carbon-heteroatom bonds, are considered: RX + E-H and E-X + RM. The potential of addition reactions of E-H or E-E to double or triple bond in C-E bond formation is also demonstrated.

Recent chemistry of four-membered ring selenium compounds is reviewed followed by a summary of work in our laboratories in this area. 2-Thia-6-selenaspiro[3.3]heptane has been synthesized for the first time. X-ray structures for the latter compound as well as for 2,6-dithiaspiro[3.3]heptane and 2,6-diselenaspiro[3.3]heptane have been determined. These compounds are useful as "rigid-rod" ligands for coordination to transition-metal complexes.

The azomethine ylid strategy for β-lactam synthesis, which involves the fragmentation of a β-lactam-based oxazolidinone to give a carboxylated azomethine ylid, has been extended to the C(2)-unsubstituted penem scaffold associated with C(6)-exoalkylidene penems. This involved the use of S -methyl dithioformate as a reactive 1,3-dipolarophile, which was most effectively employed by initial trapping with cyclopentadiene and subsequent regeneration of S -methyl dithioformate via a retro Diels-Alder reaction in the presence of the requisite oxazolidinone. This provided access to the penam scaffold, and this overall sequence was very effectively accelerated by microwave irradiation. The synthesis of C(2)-unsubstituted penems was then accomplished by application of an oxidative elimination sequence.

An efficient synthesis of (1 R ,5 S )-6-(5-cyano-3-pyridinyl)-3,6-diaza-bicyclo[3.2.0]heptane A-366833 , a novel potent selective neuronal nicotinic receptor (NNR) agonist, is described. The enantiomerically pure pharmacophore benzyl (1 S ,5 S )-3,6-diaza-bicyclo[3.2.0]heptane-3-carbamate was successfully constructed from benzyl N -allyl- N -(2-hydroxyimino-ethyl)-carbamate through a convenient approach including an intramolecular [1,3]-dipolar cycloaddition, reductive ring-opening reaction, chiral resolution, and intramolecular cyclization. Subsequent N -arylation of the pharmacophore with 3-bromo-5-cyanopyridine and N -Cbz deprotection with trifluoroacetic acid furnished A-366833 .

Two enantioselective cyanation reactions, the Strecker reaction of ketoimines and the Reissert reaction of pyridine derivatives, promoted by Lewis acid-Lewis base bifunctional asymmetric catalysts are described.

Diastereo-and enantioselective pinacol coupling reactions of chiral α-ketoamides mediated by samarium diiodide afforded extremely high diastereoselectivities. Enantiopure ( S , S )- or ( R , R )-2,3-dialkyltartaric acid and derivatives can be synthesized. Diels-Alder cycloadditions of S -indoline chiral acrylamides with cyclopentadiene in the presence of Lewis acids proceed with high diastereofacial selectivity, giving either endo-R or endo-S products depending on Lewis acid and the structures of chiral dienophiles.

An easy synthesis of 4-(1- and 2-haloalkyl)azetidin-2-ones by a [2+2] cycloadditon protocol is described. Starting from these functionalized β-lactams, new pathways toward bicyclic β-lactams were developed via intramolecular nucleophilic substitutions and radical cyclizations. 4-(1- and 2-Haloalkyl)azetidin-2-ones also proved to be very useful starting products in the synthesis of various highly substituted aziridines, azetidines, and alkenoates.

Oxolane and oxane units in oxacyclic natural products were prepared via radical cyclization reaction of β-alkoxyacrylates, β-alkoxymethacrylates, and β-alkoxyvinyl ketones.

Alternating regioregular silylene-spaced divinylarene copolymers [(donor-SiMe 2 -) n =1-3 -(acceptor-SiMe 2 )] are synthesized by rhodium-catalyzed hydrosilylation of bis-alkynes with bisvinylic silyl hydrides. Efficient intrachain energy transfer has been observed in these copolymers. The intensities of emission profiles depend on the relative ratio of donor-to-acceptor chromophores. The corresponding inorganic/organic hybrid materials are synthesized, and their photophysical properties are described.

This account outlines the results obtained in the author's laboratory on the asymmetric cyclopropanation of enantiopure 1-phosphorylvinyl p -tolyl sulfoxides with sulfur ylides and diazoalkanes. Based on experimental results and theoretical calculations, the transition-state model for asymmetric cyclopropanation is proposed. A great synthetic value of the reaction investigated is exemplified by the total synthesis of constrained analogs of bioactive compounds, namely, enantiopure cyclic analog of phaclofen and cyclopropylphosphonate analogs of nucleotides.

An overview of the synthesis, physical properties, and use as material for organic light-emitting diodes (OLEDs) of linear organic π-conjugated systems incorporating phosphole and thiophene rings is presented.

In the aza-Morita-Baylis-Hillman reaction of N -sulfonated imines with methyl vinyl ketone (MVK) promoted by chiral phosphine Lewis base: ( R )-2'-diphenylphosphanyl-[1,1']binaphthalenyl-2-ol ( LB1 ) (10 mol %), the aza-Morita-Baylis-Hillman adducts were obtained in good yields with high ee (70-94 % ee) at -30 °C in THF. The scope and limitations of this reaction have been disclosed.

Different chiral camphorsulfonamide derivatives containing a hydroxy or a sulfonamido functionality, as well as chiral 1,2-hydroxysulfonamides, have been evaluated as chiral promoters in the classical enantioselective addition of dialkylzinc reagents to aldehydes in the presence of titanium tetraisopropoxide (ee up to 96 %). Surprisingly, ligands with a structure of isoborneol are able to promote the related unknown addition to ketones (ee >99 %), the best ligand being the exo -diol derived from 1,2- trans -biscamphorsulfonamidocyclohexane (HOCSAC).

Chiral spiro phosphorus ligands including monophosphoramidites and diphosphines, which contained 1,1'-spirobiindane as a backbone, were designed and synthesized. These spiro ligands were proven to be highly efficient for rhodium- and ruthenium-catalyzed asymmetric hydrogenations of prochiral olefins and ketones with excellent enantioselectivities.

Information storage in chemical and biological systems involves recognition processes occurring at the molecular and macromolecular level. The implementation of a "code" can consist of multiple noncovalent interactions, which include hydrogen bonds, π-stacking, hydrophobic interactions, and appropriate molecular and supramolecular architectures. With the double-helical DNA structure stabilized by Watson-Crick hydrogen bond base-pairing and aryl π-π stacking interactions, nature provides to scientists an example of one of the most sophisticated supramolecular systems. Molecular organization using these types of processes has become a very powerful strategy for the construction of well-defined nanostructures. Self-assemblies using noncovalent interactions have been designed to build fibers, membranes, two-dimensional monolayers, hydro, organo gels, etc. This paper highlights the research presented at the workshop entitled DNA Supramolecular Assemblies, which was held in Avignon, France on 5-6 May 2004. In this article, we first focus on the recent progress achieved in the design of supramolecular self-assemblies that mimic the molecular recognition functionalities found with nucleic acids. Second, we present several synthetic-DNA supramolecular assemblies currently developed to transport nucleic acids into cells. The marriage of supramolecular chemistry with nucleic acids as illustrated through examples in this article will open new avenues for designing artificial molecular devices and expand the current repertoire of supramolecular assemblies available.

The atomic force microscope (AFM) is designed to provide high-resolution (in the ideal case, atomic) topographical analysis, applicable to both conducting and nonconducting surfaces. The basic imaging principle is very simple: a sample attached to a piezoelectric positioner is rastered beneath a sharp tip attached to a sensitive cantilever spring. Undulations in the surface lead to deflection of the spring, which is monitored optically. Usually, a feedback loop is employed, which holds the spring deflection constant, and the corresponding movement of the piezoelectric positioner thus generates the image. From this it can be seen that the scanning AFM has all the attributes necessary for the determination of surface and adhesion forces; a sensitive spring to determine the force , a piezoelectric crystal to alter the separation of the tip and surface, which if sufficiently well-calibrated also allows the relative separation of the tip and surface to be calculated. One can routinely quantify both the net surface force (and its separation dependence) as the probe approaches the sample, and any adhesion (pull-off) force on retraction . Interactions in relevant or practical systems may be studied, and, in such cases, a distinct advantage of the AFM technique is that a particle of interest can be attached to the end of the cantilever and the interaction with a sample of choice can be studied, a method often referred to as colloid probe microscopy. The AFM, or, more correctly, the scanning probe microscope, can thus be used to measure surface and frictional forces, the two foci of this article. There have been a wealth of force and friction measurements performed between an AFM tip and a surface, and many of the calibration and analysis issues are identical to those necessary for colloid probe work. We emphasize that this article confines itself primarily to elements of colloid probe measurement using the AFM.