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A convenient, rapid and widely applicable one-pot procedure has been developed for the synthesis of acetylenedicarboxamides from various primary and secondary amines, including amino acid derivatives, protected carbohydrates, and fluorescent labels. By using DMTMM for amide coupling, acetylenedicarboxylic acid was directly converted into acetylenedicarboxamides in highly competitive overall yields (52–80%).

Aldol reactions constitute a powerful methodology for carbon-carbon bond formation in synthetic organic chemistry. Biocatalytic carboligation by aldolases offers a green, uniquely regio- and stereoselective tool with which to perform these transformations. Recent advances in the field, fueled by both discovery and protein engineering, have greatly improved the synthetic opportunities for the atom-economic asymmetric synthesis of chiral molecules with potential pharmaceutical relevance. New aldolases derived from the transaldolase scaffold (based on transaldolase B and fructose-6-phosphate aldolase from Escherichia coli) have been shown to be unusually flexible in their substrate scope; this makes them particularly valuable for addressing an expanded molecular range of complex polyfunctional targets. Extensive knowledge arising from structural and molecular biochemical studies makes it possible to address the remaining limitations of the methodology by engineering tailored biocatalysts.

In bissecododecahedra-1,10(11)-dienes, the syn-periplanar and unusually proximate arrangement of the π bonds is responsible for extraordinary physical properties such as strong throughspace homoconjugation, low oxidation potentials, and a special reactivity pattern. In pursuit of route B to dodecahedranes[1], the hyperstability predicted (MM2) for these bissecodienes and the related monoenes has been experimentally verified only for the latter in their resistance towards catalytic hydrogenation. Non-hydrogenative saturation of (3,8-difunctionalized) bissecodienes (3, 8, 13) and monoenes (4, 9, 14) becomes increasingly hampered due to the increased steric congestion on the more spherical molecular surfaces but can be achieved in „high-driving-force” reactions [cis-hydroxylation (26, 27, 41, 42), epoxidation (38, 54, 57, 58, 60, 63, 80, 83), cyclopropanation (55, 59, 61, 64]. In contrast, cycloadditive four-, five- (73), and six-membered (76) ring annulation again is limited to monoadditions. The half-cages in the bissecododecahedrane structures provide for remarkable steric steering and protection [e.g. anti-selective protonation (alkylation) of carbanions 57a (84a)2-, lack of hydrazone formation from ketones 58, 89, resistance of syn-bis(acid chloride) 86 towards hydrolysis.

Three conceptual routes (A, B, C) from [1.1.1.1]pagodane (1) to pentagonal dodecahedrane (2) are evaluated by MM2 (MM3) calculations. After limited experimental success with a catalytic one-pot route (A), a more selective transformation along one of two stepwise routes (B/C) is explored. An expeditious entry into route C is achieved by hydrogenolytic cyclobutane opening in 1; secopagodane 7 (100%), however, resists both progression along route C (dehydrogenative C—C bond formation to isododecahedrane 8) and crossover into route B (hydrogenolysis to bissecododecahedrane 5). The first transformation along route B, the 2sigma;2π-isomerization of the highly strained 1 to bissedodecahedra-1,10(11)-diene 3, is not attainable by metal catalysis and cannot productively be brought about by thermal activation: The necessarily very high reaction temperatures (> 700°C) enforce instead a mechanistically interesting fragmentation into two C10H10 halves to give ultimately naphthalene. The very rapid pagodane opening occurring after one-electron oxidation, too, is not a preparatively useful alternative. Highly efficient, on the other hand, is a two-step process affording a high yield of the product and consisting of regiospecific, photochemically induced bromine addition to the central four-membered ring ( dibromosecopagodane 37) followed by reductive bromine elimination ( diene 3). In spite of the necessarily rather severe reaction conditions in both steps, this procedure is applicable to the preparation of various 3,8-difunctionalized bissecodienes (dienedione 11, diene diesters 43, 50, 52, dichlorodiene 56). Limitations of this procedure are met with the 4,4,9,9-tetrachloropagodane 60 (inert) and the [2.2.1.1]pagodane 80 (bridgehead bromination). The lateral half-cages of the (seco)-pagodane structures are explored for preparatively (dis)advantageous steric effects, that might be later exploited on the way towards functionalized dodecahedrane derivatives.

The C=O stretching frequencies of substituted benzoylketene-S,S-dimethylacetals (1a–1o) and benzoylketene-S,S-ethyleneacetals (2a–2m) were measured in CHCl3 and CCl4 and correlated with theHammett substituent constants. The correlations were split into two different and well separated lines for compounds containing electron donor and electron acceptor substituents, which were assigned tos-trans ands-cis quasiplanar conformations. The correlations of carbonyl stretching frequencies with C=O bond orders and oxygen atom charge densities calculated using the semiempirical AM1 method reveal similar results consistent with assignments of structures1 and2 to two quasiplanar conformations. The preparation of some new benzoylketene-S,S-acetals is reported as well.

Catalytic aldol reactions are among the most useful synthetic methods with a high potential for convergent asymmetric synthesis. As an increasing number of lyases is becoming available for preparative applications, in this review the state of the art concerning the application of these biocatalysts for enzymatic C-C bond formations is evaluated. The scope, and the individual limitations, of the most important types of enzyme-catalyzed transformations are discussed against a more recent mechanistic and protein-structural background. Special emphasis is placed on the synthetic power of a stereodivergent building-block approach which is facilitated by the prevalence of families of stereocomplementary enzymes which often have a very similar, broad substrate tolerance. The methodology is highlighted by exemplary applications to the synthesis of valuable polyfunctionalized products which otherwise are difficult to prepare and to handle by classical chemical methods.

Catalytic aldol reactions are among the most useful synthetic methods for highly stereocontrolled asymmetric synthesis. In this account we discuss the recent development of a novel synthetic technique which uses tandem enzyme catalysis for the bi-directional chain elongation of simple dialdehydes and related multi-step procedures. The scope and the limitations of multiple one-pot enzymatic C-C bond formations is evaluated for the synthesis of unique and structurally complex carbohydrate-related compounds that may be regarded as metabolically stable mimetics of oligosaccharides and that are thus of interest because of their potential bioactivity.

A single step approach for the diastereoselective synthesis of C-glycosidic sugar phosphonates was developed by utilizing a free radical coupling to dialkyl vinylphosphonates to give the title compounds in moderate yield. The method is broadly applicable to sugars, deoxysugars, aminosugars, and oligosaccharides.

The present review outlines, on the basis of specific examples taken from our laboratory, the most important steps in (i) preparing supported nanoassembled model catalysts and (ii) investigating their size-dependent catalytic properties. We describe the cluster generation and present evidence for softlanding of the clusters onto solid surfaces. Subsequently, the growth and the characterization of the cluster support material, thin magnesium oxide films, are discussed, including the role of surface defects. Then the thermal stability of Cu clusters and the individual electronic structure of small Ag and Cu clusters on MgO are addressed. Finally, two examples of cluster size-dependent heterogeneous catalytic reactions are presented, (i) the cyclotrimerization of acetylene on nanoassembled Pd catalysts, and (ii) the CO oxidation on nanoassembled Au catalysts. We show experimentally and together with first-principle calculations that the interaction of such small metal clusters with the oxide surface strongly changes their catalytic properties. In contrast to large particles an additional electron in localized valence states of small clusters represents a major change. It is this charge transfer which turns inactive gold and palladium clusters into active model catalysts opening new perspectives to tune catalytic processes on the nanoscale.

The present critical review examines the status of the research on supported, size-selected clusters with specific emphasis on their size-dependent physical and chemical properties. We describe the most relevant experimental methods with their advantages and drawbacks for the production of size-selected clusters and look critically at the present evidence for soft-landing of the clusters onto solid surfaces. Growth and characterization of cluster support materials are surveyed and the important role of surface defects for the properties of the supported clusters is considered. Recent advances in the characterization of the supported, size-selected clusters with local and non-local surface science analytical tools are presented and a few illustrative examples for size effects are given. Of specific and possibly broad impact on heterogeneous catalysis, we consider the discovery of the size-dependence of chemical reactions on very small supported clusters where recent experimental and theoretical evidence in...

Amido-alkylation of electron-rich arenes with phenylacetamide and glyoxylic acid offers an inexpensive route to a large variety of N-phenylacetylated arylglycines that are suited for immediate enzymatic resolution by penicillin G acylase. When performed under mild conditions at 5°C in acetic acid/ HCl, this simple one-pot operation resulted in the formation of single regioisomers only (≥98%). Subsequent kinetic resolution of the amino acid derivatives by penicillin G acylase at pH 8.0 occurred generally with E values > 100 and thus furnished free (S)-configurated arylglycines with high enantiomeric purity. The corresponding enantiopure (7?)-substrates, easily separable by a phase-selective extraction process, provided the corresponding (/?)-enantiomers upon conventional hydrolysis. This one-pot, two-step procedure for arylglycine synthesis, resolution and work-up requires a minimum of equipment and grants rapid access to both enantiopure (S)- and (R)-antipodes of non-natural α-amino acids in small-to large-scale quantities.

Acylation of aromatic amines 1 with diisopropyl malonate (2) leads to a mixture of isopropyl N-arylmalonamates 3 and malonanilides 4. The reaction of 3 with carbon disulfide in the presence of sodium hydride gives disodium salts 5. Treatment of 5 with an alkylating agent yields the open-chain or cyclic ketene dithioacetals 6, 7 or 8. The molecular structure, hydrogen bonding and preferential conformation of the isopropyl N-arylmalonamates 3, 6 and 7 were investigated using correlation analyses of IR, 13C NMR and AM1 semiempirical data.

The Gram-positive bacterium Listeria monocytogenes is primarily a saprophyte living on decomposing organic matter. This mirrors the lifestyle of Bacillus subitilis, a soil bacterium to which Listeria monocytogenes is genomically closely related. In contrast to B. subtilis, which as a strict aerobe does not colonize the mammalian gut, L. monocytogenes is a facultative intracellular bacterium. It gains access to the gastrointestinal tracts of a wide variety of mammalian hosts, including humans, through consumption of contaminated food. This is a particular problem for the food industry as L. monocytogenes is able to survive both at low temperatures and high salt concentrations. By recognizing and adhering to epithelial cells lining the intestine, it escapes being expelled from the host intestine by the normal excretory route (Figure 1, step 1). The participation of one