An efficient synthesis of indane-derived bis(oxazoline) and its application to hetero Diels-Alder reactions on polymer support

Indane-derived bis(oxazolines) were synthesized in two steps and 93% overall yield starting from commercially available substrates. This ligand is as effective as tert-butyl bis(oxazoline) in hetero Diels-Alder reaction both in solution and on polymer support.     

State-transition categories

This paper presents the idea to define a category which is related to a state-transition system. To represent our knowledge, we also introduce knowledge functions and fuzzy knowledge functions.     

Penicillin-cephalosporin conversion-XI. Synthesis of 7-(α-substituted phenylacetoamide) cephalosporins by utilization of all the framework elements of penicillin G

A successful synthesis of clinically significant cephalosporins 2a-c with use of all the framework elements of penicillin G is described.     

Effects of encounters on phase separation dynamics from diffusion-controlled growth to coarsening

We investigate the dynamics of phase separations in quenched binary mixtures, such as binary alloys and polymer blends with low mobilities, at higher volume fractions. Computer simulations are performed using simple model equations in the presence of encounters of droplets. Four characteristics stages with three crossovers, including dynamical scaling behavior and temporal power laws, are found beyond a volume fraction of approximately 0.14, where each crossover is attributed to a transition from one growth mechanism to the other. The encounter effect is thus shown to strongly influence a transition from the diffusion-controlled (t^1/2) stage to the coarsening (t^1/3) stage. A simple analytical argument for the simulation results is also presented.     

Synthesis and Stereochemical Revision of the C31–C67 Fragment of Amphidinol 3

Amphidinol 3 (AM3) is a marine natural product produced by the dinoflagellate Amphidinium klebsii. Although the absolute configuration of AM3 was determined in 1999 by extensive NMR analysis and degradation of the natural product, it was a daunting task because of the presence of numerous stereogenic centers on the acyclic carbon chain and the limited availability from natural sources. Thereafter, revisions of the absolute configurations at C2 and C51 were reported in 2008 and 2013, respectively. Reported herein is the revised absolute configuration of AM3: 32S, 33R, 34S, 35S, 36S, and 38S based on the chemical synthesis of partial structures corresponding to the C31–C67 fragment of AM3 in combination with degradation of the natural product. The revised structure is unique in that both antipodal tetrahydropyran counterparts exist on a single carbon chain. The structural revision of AM3 may affect proposed structures of congeners related to the amphidinols.     

On minimum and maximum spanning trees of linearly moving points

In this paper we investigate the upper bounds on the numbers of transitions of minimum and maximum spanning trees (MinST and MaxST for short) for linearly moving points. Here, a transition means a change on the combinatorial structure of the spanning trees. Suppose that we are given a set ofn points ind-dimensional space,S={p ₁,p ₂, ...p _n }, and that all points move along different straight lines at different but fixed speeds, i.e., the position ofp _i is a linear function of a real parametert. We investigate the numbers of transitions of MinST and MaxST whent increases from-∞ to +∞. We assume that the dimensiond is a fixed constant. Since there areO(n ²) distances amongn points, there are naivelyO(n ⁴) transitions of MinST and MaxST. We improve these trivial upper bounds forL ₁ andL _∞ distance metrics. Letk _p (n) (resp. ) be the number of maximum possible transitions of MinST (resp. MaxST) inL _p metric forn linearly moving points. We give the following results in this paper: κ₁(n)=O(n ^5/2 α(n)),κ _∞(n)=O(n ^5/2 α(n)), , and where α(n) is the inverse Ackermann's function. We also investigate two restricted cases, i.e., thec-oriented case in which there are onlyc distinct velocity vectors for movingn points, and the case in which onlyk points move.     

A PM3 study on intrinsic decarboxylation process of methyl–ethyl-α–pyridylacetic acid

To probe the decarboxylation process of methyl–ethyl–α pyridylacetic acid (MEPA), molecular orbital calculations on the optimized geometry, transition-state geometry, and intrinsic reaction coordinate were performed by the MNDO –PM 3 method. The salient features of the optimized structure of MEPA are that the carboxyl anion is nearly on the plane of the pyridine ring (the dihedral angle of C8? C7? C2? N1 is 14.7°) and that the interatomic distance

1 …? is used for a noncovalent bond, such as N⁺ 1 …? O^?9.

of O^?9 …? H1′ is 1.6 Å (exchange of electrons exists between their atoms). The transition-state geometry of the decarboxylation process has the following features: (1) the activation enthalpy is 6.0 kcal/mol, (2) the dihedral angle of C8? C7? C2? N1 is ?50.2°, and (3) the interatomic distance of O^?9? H1′ and C7? C8 increase by 111 and 124%, respectively, as compared with the optimized geometry. From the extreme beginning of the intrinsic decarboxylation process, the exchange of electrons between O^?9 …? H1′ begins to decrease. This decrease, which is considered to be induced by the rotation of C2? C7, seems to initiate the dissociation of C7? C8. © 1995 John Wiley & Sons, Inc.     

High-pressure polymerization of vinyl chloride

The radical polymerization of vinyl chloride was investigated at 60°C under high pressure up to 5000 bar in benzaldehyde, benzonitrile, toluene, heptane, cyclohexane, and dioxane as solvent. In benzaldehyde and benzonitrile, the polymerizations were depressed by increased pressure. This unusual behavior was explained by the solvent participation and the effect of pressure on the propagating radicals. The crystallinities of polymer obtained in all solvents decreased with increasing pressure, as judged by the absorbance ratio of the infrared spectra. However the effects of pressure on the absorbance ratio of the polymer obtained in benzaldehyde and benzonitrile were not identical with those in the other solvents. These facts also suggest that both solvents play a special role for the solvent participation in the propagating step.