Chemoselective construction of substituted conjugated dienes using an olefin cross-metathesis protocol

[Reaction: see text] Various substituted conjugated dienes have been made by olefin cross-metathesis. Using either electronic or steric "protection," one of the olefins of the conjugated diene was deactivated relative to the other for cross-metathesis. The reactions proceed with very high chemoselectivity and, when steric deactivation is used, very high diastereoselectivity.     

Physical properties of many-electron atomic systems evaluated from analytical Hartree-Fock functions

The promotion energies, ionization potentials, electron affinities, and orbital electronegativities for the valence states of importance in atoms of the first two rows of the periodic system have been evaluated from analytical Hartree-Fock functions for the corresponding groundstates. The agreement with existing values, determined from experimental data, is very satisfactory.This work has been supported in part by the National Research Council of Canada.     

The simplest coronoids: Hollow hexagons

Hollow hexagons form a subclass of primitive coronoid systems. The macrocyclic aromatic hydrocarbon kekulene corresponds to a hollow hexagon. The hollow hexagons for given numbers of hexagonal units (h) were enumerated by computer aid, but also an analytical solution for the numbers of hollow hexagons was achieved. For the Kekulé structure counts (k) of a hollow hexagon a general formula is reported. Also the maximum and minimumK numbers are considered.This article is Part VI of the series Enumeration and Classification of Coronoid Hydrocarbons. For Part V, see ref. [36].     

Mamanine and pohakuline,two unprecedented quinolizidine alkaloids from sophorachrysophylla

From the bark of the endemic Hawaiian tree Sophora chrysophylla Seem. we have isolated two unprecedented quainolizidine alkaloids, mamanine (4) and pohakuline (5). Both bases are 1-hydroxymethylenequinolizidines which are linked at C-3 to α-pyridone or α-piperidone moieties. The alkaloids may be intermediates in a heretofore unknown biogenetic pathway of Sophora alkaloids.     

Preparation and chemistry of phosphoranyl-derived iodanes

The preparation and chemistry of novel phosphoranyl-derived lambda(3)-iodanes is reported. The phosphoranyl-derived phenyliodonium sulfonates were prepared in good yields by the reaction of stabilized phosphonium ylides [1-triphenylphosphoranylidene-2-propanone, methyl(triphenylphosphoranylidene)acetate, (triphenylphosphoranylidene)acetaldehyde, and (triphenylphosphoranylidene)acetonitrile] with the pyridinium complex of iodobenzene ditriflate or with [hydroxy(tosyloxy)iodo]benzene under mild conditions. These compounds represent a potentially useful class of reagents that combine in one molecule synthetic advantages of a phosphonium ylide and an iodonium salt. Specifically, phosphorane-derived phenyliodonium tosylates can react with soft nucleophiles, such as iodide, bromide, benzenesulfinate, and thiophenolate anions, with a selective formation of the respective alpha-functionalized phosphonium ylides, which can be further converted to alkenes by the Wittig reaction with benzaldehyde. The phosphoranyl-derived benziodoxoles can be prepared by the reaction of 1-acetoxybenziodoxole with stabilized phosphonium ylides. An unusual ligand exchange on the iodine(III) center resulting in the substitution of a carbon ligand with an oxygen ligand was observed in the reaction of these compounds with strong acids.