1‐Phenyl‐1,2‐cyclohexadiene: Astoundingly High Enantioselectivities on Generation in a Doering–Moore–Skattebøl Reaction and Interception by Activated Olefins

The resolution of (1α,5α,6α)‐6‐bromo‐6‐fluoro‐1‐phenylbicyclo[3.1.0]hexane (rac‐ 5) provided the enantiomerically pure precursors (?)‐ 5 and (+)‐ 5 of 1‐phenyl‐1,2‐cyclohexadiene. On treatment of (?)‐ 5 with methyllithium in the presence of 2,5‐dimethylfuran, the pure (?)‐enantiomer of the [4+2] cycloadduct of 2,5‐dimethylfuran onto 1‐phenyl‐1,2‐cyclohexadiene was obtained exclusively. From this result, it is concluded that pure (M)‐1‐phenyl‐1,2‐cyclohexadiene ((M)‐ 7 ) emerged from (?)‐ 5 and was enantiospecifically intercepted to give the product. In the case of indene as trap for (M)‐ 7 , the (?)‐ and the (+)‐enantiomer of the [2+2] cycloadduct were formed in the ratio of 95:5. Highly surprising, remarkable enantioselectivities were also observed, when (M)‐ 7 was trapped with styrene to furnish two diastereomeric [2+2] cycloadducts. Hence, the achiral conformation of the diradical conceivable as intermediate cannot play a decisive part. The enantioselective generation of (M)‐ and (P)‐ 7 by the β‐elimination route was tested as well. Accordingly, 1‐bromo‐2‐phenylcyclohexene was exposed to the potassium salt of (?)‐menthol in the presence of 2,5‐dimethylfuran, and the enantiomeric [4+2] cycloadducts of the latter onto (M)‐ and (P)‐ 7 were produced in the ratio of 55:45.     

Synthesis of pseudo-C-nucleosides from β-formyl-α,β-unsaturated ester bearing a β-furanosidic moiety

Abstract  

Pseudo-C-nucleosides have potential biological activity, and an efficient synthesis of new pseudo-C-nucleosides has been developed via the reaction of a β-formyl-α,β-unsaturated ester bearing a β-sugar moiety with hydrazines in neutral and acidic conditions. The preparation of the β-formyl-α,β-unsaturated ester was accomplished by oxidation of the secondary hydroxyl group of 3-O-benzyl-1,2-O-isopropylidene-α-d-glucofuranose, followed by elongation of its carbon chain with (ethoxycarbonylmethylene)triphenylphosphorane and oxidation of the hydroxymethyl group.     

Amphiphilic polymers based on higher alkylene oxides: Synthesis and characterization by different chromatographic techniques

Homopolymers and block copolymers of higher epoxides (butene oxide and hexene oxide) are synthesized using 1-alkanols and polyethylene glycol monomethyl ether (PEG-MME) 1100 as initiators by anionic ring opening polymerization in bulk. Most of the samples were synthesized with controlled microwave heating in sealed vessels. Tri- and tetrablock copolymers with different repeat units in the individual blocks are synthesized by living polymerization with addition of the next monomer after complete consumption of the previous one. The products thus obtained are characterized using size exclusion chromatography (SEC), liquid chromatography under critical conditions (LCCC) and liquid adsorption chromatography (LAC).     

Characterization of ethylene oxide–propylene oxide block copolymers by combination of different chromatographic techniques and matrix-assisted laser desorption ionization time-of-flight mass spectroscopy

Block copolymers of ethylene oxide (EO) and propylene oxide (PO) are characterized by combination of two-dimensional chromatography and MALDI-TOF-MS. Liquid chromatography under critical conditions (LCCC) is used as first dimension and fractions are collected, mobile phase evaporated and diluted in the mobile phase used in second dimension (SEC or LAC). This two-dimensional chromatography in combination of MALDI-TOF-MS gives information about purity of reaction products, presence of the byproducts, chemical composition and molar mass distribution of all the products.     

Ambrox®

Ambergris, obtained from the intestinal tract of the sperm whale, is a highly esteemed fragrance since several millennia. The olfactory most important ingredient of ambergris is Ambrox^®, which is produced on large scale by partial synthesis from sclareol from clary sage. The polyene cyclisations of homofarnesol and homofarnesylic acid are highly attractive total syntheses of Ambrox^® and sclareolide. 5,5a‐Dehydroambrox is an outstanding new scent, both to its distinguished fragrance properties and its elegant total syntheses.     

Pivoting in Linear Complementarity: Two Polynomial-Time Cases

We study the behavior of simple principal pivoting methods for the P-matrix linear complementarity problem (P-LCP). We solve an open problem of Morris by showing that Murty’s least-index pivot rule (under any fixed index order) leads to a quadratic number of iterations on Morris’s highly cyclic P-LCP examples. We then show that on K-matrix LCP instances, all pivot rules require only a linear number of iterations. As the main tool, we employ unique-sink orientations of cubes, a useful combinatorial abstraction of the P-LCP.     

Γ-convergence of Variational Integrators for Constrained Systems

For a physical system described by a motion in an energy landscape under holonomic constraints, we study the Γ-convergence of variational integrators to the corresponding continuum action functional and the convergence properties of solutions of the discrete Euler–Lagrange equations to stationary points of the continuum problem. This extends the results in Müller and Ortiz (J. Nonlinear Sci. 14:279–296, 2004) to constrained systems. The convergence result is illustrated with examples of mass point systems and flexible multibody dynamics.      

Energy–vector method in mechanical oscillations

The new conception of the space, and its construction are introduced. The space allows for a geometrical view on energy changes in mechanical vibrating systems. It posses all the possibilities of the system dynamics analysis that are used in the traditional phase space but it also shows an amount of the energy accumulated in the system, an energy changes, flow, dissipation, synchronization, an energy attractors. Thus it increases our knowledge and intuition on energy changes in vibrating systems. Dynamics of the chaotic system is studied using the energy space. New types of maps are introduced.