Formal intramolecular [5 + 2] photocycloaddition reactions of maleimides: a novel approach to the CDE ring skeleton of (-)-cephalotaxine

A concise approach to the cephalotaxine CDE ring skeleton based on the intramolecular formal [5 + 2] photocycloaddition of cyclopentenyl-substituted maleimides is described. An investigation of the diastereoselectivity afforded by various protected alkoxy groups demonstrated that the best selectivity (3.5:1) was afforded by the free hydroxyl group, strongly suggesting a hydrogen-bonded excited state. Reaction: see text.     

Homopolymerisation von Maleins?ureanhydrid

Ohne Zusammenfassung     

A weight-function approach for determining watershed initial conditions for combustion waves

In many generic combustion models, one finds that a combustionwave will develop with a specific wave speed. However, thereare possible initial temperature profiles which do not evolveinto such waves, but rather die out to the ambient temperature.There can exist, in some models, a clear distinction betweenthose initial conditions that do evolve into combustion wavesand those that do not; this is sometimes referred to as thewatershed initial condition. When fuel consumption is consideredto be negligible, analytical methods can be used to obtain theexact watershed. In this paper, we consider the problem of determiningpseudo-watersheds and ascertaining the relationship betweenthese pseudo-watersheds and the exact watersheds. In the processa novel weight-function approach for infinite spatial domainsis developed.     

Copolymerization Parameters of Itaconic Anhydride in Free-Radical Polymerization

The copolymerization of itaconic anhydride (M₁) with four different monomers (M₂), namely: vinyl acetate, 2-chloro-ethyl acrylate, acrylonitrile, and styrene, was studied. Values of r₁ and r₂ were determined for copolymerizations in benzene and for two of these systems, namely those with vinyl acetate and 2-chloroethyl acrylate. Values of r₁ and r₂ were also determined for copolymerizations in tetra-hydrofuran. The value of ri ranged from 0.53 to 4.8, but it was always very much greater than r2. The Q-e values for itaconic anhydride in all the systems studied were also calculated and the average values for Q₁ = 8.2, e₁ = 1.45 were determined.     

Synthesis of cytotoxic cyanobactin,Wewakazole B

We report herein the synthesis of cytotoxic cyanobactin, Wewakazole B through an efficient solution-phase approach. The key steps of the synthesis are the macrocyclic lactamization of linear dodecapeptide and construction of two hexapeptides with three different substituted oxazole rings.     

Bestimmung der Copolymerzusammensetzung mittels quantitativer IRAnalyse

Ohne Zusammenfassung     

Homopolymerization of Maleic Anhydride

It is well known that molecular oxygen inhibits the homopolymerization of vinyl-type monomers [1]. During several attempts in this laboratory to homopolymerize vinyl acetate in benzene, no polymer was formed over a period of one week, even though the initiator was varied as to type and concentration.     

Copolymerisation von Itaconsäuréanhydrid und Styroi,Bestimmung der Reaktivitätsverhältnisse

Ohne Zusammenfassung     

Copolymerisations-Parameter von Itakonsliureanhydrid bei der Polymerisation mit freien Radikalen

Ohne Zusammenfassung     

Unipolar Arc Tracks on Stainless Steel

Craters caused by unipolar arcs on stainless steel depend strongly on surface conditions. There are three diameter distributions: Small craters (～ 0.3 μm) for oxidised surfaces, larger craters (～ 2 μm) for moderately cleaned areas, and very large craters (～ 20 μm) for clean surfaces. These values are compatible with Joule heating models of crater formation. Compared with other metals of interest, stainless steel shows the largest craters.