Lewis base activation of lewis acids. Addition of silyl ketene acetals to aldehydes

The weak Lewis acid silicon tetrachloride can be activated by catalytic amounts of the chiral bisphosphoramide (R,R)-3 to form a highly reactive, chiral trichlorosilyl cation which is an extremely effective promoter of aldol addition reactions between aldehydes and silyl ketene acetals. The tert-butyldimethylsilyl ketene acetal of methyl acetate adds nearly instantaneously to aromatic and olefinic aldehydes as well as aliphatic aldehydes (albeit more slowly) with excellent enantioselectivity. The homologous tert-butyldimethylsilyl ketene acetal of tert-butyl propanoate adds with nearly exclusive anti diastereoselectivity to a similar range of aldehydes also with excellent enantioselectivity. The origin of the slower reaction rate with aliphatic aldehydes is revealed to be the formation of chlorosilyl ether adducts.     

The use of polarized light scattering for the study of the dynamics of the spinodal decomposition

Due to the fact that in a system undergoing spinodal decomposition the long wavelength fluctuations are enhanced, we expect that multiple events can be observed when the passage of light through the sample is measured. We study here the intensity of double scattering for both polarized and depolarized measurements, as a function of time and angle of detection. The time dependence is nonexponential and the dependence on the scattering wave vector is less pronounced than in the case of single scattering. For systems with spherical molecules it is possible to separate double and single scattering contributions if both polarized and depolarized measurements are made. This increases the amount and quality of information about the dynamics of the spinodal decomposition that can be obtained from light scattering experiments.     

Synthesis of (±)-aporphine utilizing Pictet-Spengler and intramolecular phenol ortho-arylation reactions

A synthesis of the alkaloid (±)-aporphine is reported. The initial key step of the synthesis involves a Pictet-Spengler cyclization of N-tosyl tyramine with 2-bromophenylacetaldehyde in trifluoroacetic acid. This step was followed by the second strategic transformation a palladium-mediated intramolecular phenol ortho-arylation reaction utilizing tricyclohexylphosphine as co-catalysts in the presence of cesium carbonate. Finally, de-oxygenation of the phenol, removal of the tosyl group and methylation gave the desired alkaloid.     

A high resolution mass spectrometric measurement system for a vacuum fusion apparatus

A high resolution mass spectrometric read-out system for a vacuum fusion apparatus is described. Rapid analyses are possible and the rate at which various gases are evolved can be monitored. Gas mixture assays are accomplished by scanning the nominal mass 28 peak. Serial measurements of CO⁺, N₂⁺ and C₂H₄⁺ are made. Thus detection and measurement of evolved hydrocarbons are possible. The results for silver and tin from a conventional vacuum fusion apparatus and the mass spectrometer apparatus are compared.     

Untersuchungen über ternäre Chalkogenide. XXIV. Zur Struktur des TlGaSe2

On Ternary Chalcogenides. XXIV. The Structure of TlGaSe₂ TlGaSe₂ is monoclinic with a = 10.772(3), b = 10.771(5), c = 15.636(8) Å, ß = 100.6(3)°, Z = 16, space group Cc. The refinement yielded an R value of 0.082 for 1366 unique observed reflections (MoKα). The compound crystallizes with a layer structure with two anion layers perpendicular to c* in the unit cell. The structural motive of the layers are large corner-linked Ga₄Se₁₀- tetraeder consisting of four corner-linked GaSe₄ tetrahedra. Two adjacent layers are turned relative to each other by 90°. They are kept together by Tl¹⁺ ions, which are situated on straight lines parallel to the edges of the Ga₄Se₁₀ groups. They are surrounded by six selenium atoms forming trigonal-prismatic TlSe₆ polyhedra. 4₂ screw-axes within the layers are the reason for a strongly pronounced pseudo tetragonal symmetry. Different possibilities of stacking cause a onedimensional disorder along the c* direction. The relations between the TlGaSe₂ type and the TlSe type and also the high-pressure modifications of some compounds with the TlGaSe₂ structure are discussed.     

Synthesis and structure of pyrazolo[5,1-a]isoindol-8-ones from Aromatic Ortho Diesters

The title compounds 2 , have now been shown to arise in certain cases from condensation of aromatic ortho-diesters with ketone, where formerly only indeno[1,2-c]pyrazol-4(1H)-ones 3 have been reported from such reaction. Heretofore 2 was obtained in a less direct fashion from phthalaldehydic acid esters. When hetero-aromatic diesters were employed, new heterocyclic ring systems as represented by 2a,b ,c were prepared for the first time. Structures of 2 have been verified from detailed ¹H and ¹³C nmr studies, while representative intermediates 4–9 in the condensation of diesters to 2 have been isolated and identified.     

The numbers of chiral and achiral alkanes and monosubstituted alkanes

Whereas the theory for the enumeration of the optical isomers of the lakyl radicals and the alkanes has long been understood, this is not the case for the corresponding archiral isomers. We present for the first time recurrence formulae for counting the number of archiral isomers of the alkyl radicals and the alkanes. For chiral and archiral alkanes and monosubstituted alkanes, numerical results up to C₁₄ are tabulated.After presenting the history of the problem and the necessary definitions, we proceed to derive functional equations on the various generating functions, which readily yield the more explicit recurrence formulae usefule for numerical calculations. In the process, we first re-derive Pólya's expression for planted steric trees using his classical enumeration theorem. This result is then extended to the enumeration of free steric trees using the now standard tree-counting method due to Otter and known as a dissimilarity characteristic equation.By definition, a steric tree is a quartic tree (all points having degree 1 or 4) in which the four neighbors of every carbon point are given a tetrahedral configuration. Building on the methods of the first two authors for counting chiral and archiral trees in the plane, we obtain the formula for counting achiral steric trees, thus setting a problem first enunciated by van't Hoff and Le Bel in 1874.     

Atmospheric radioactive isotopes at orbital altitudes

The radioactive isotope ⁷Be was discovered on the forward-facing side of the LDEF satellite in amounts far exceeding that expected from direct cosmic ray activation of the spacecraft material. This prompted an examination of the production of cosmogenic isotopes in the atmosphere and of the processes by which they may be transported to orbital altitudes and absorbed by a spacecraft. ⁷Be is only one of several atmospheric cosmogenic isotopes that might be detectable at orbital altitudes and that might prove to be as useful as tracers of atmosphere ciculation processes in the mesosphre and thermosphere as they have been in the lower layers of the atmosphere.     

Novel boron heterocycles. II. 2,3-dihydro-1,3,5,2-oxadiazaboroles, 1,2-dihydro-1,3,2-benzodiazaborine 3-oxide,and 3,4-dihydro-2H-1,2,4,3-benzothiadiazaborine 1,1-dioxide

A number of arylamidoximes, an o-aminobenzaloxime, and an o-aminobenzenesulfonamide have been reacted with boronic acids to give three novel boron containing heterocycles. Evidence, based on mass spectroscopy, that the product from o-aminobenzaloxime is a 1,2-dihydro-l,3,2-benzodiazaborine 3-oxide, is presented.