Synthesis of the ABC ring system of Azaspiracid. 2. A systematic study into the effect of C(16) and C(17) substitution on bis-spirocyclization

[reaction: see text] A systematic study into the effect of C(16) and C(17) substitution on the stereochemical outcome of bis-spirocyclization to form the ABC ring system of azaspiracid is disclosed. Successful construction of the natural 10R,13R bis-spirocyclic stereochemistry has been accomplished on the C(16) benzyloxy-containing precursor.     

pi-Ligands for generating transition metal-peptide complexes: coordination of amino acid derivatives to tungsten utilizing alkyne ligands

[structure: see text] Amino acid derivatives bearing an alkyne (AA-CCH) at either the N- or C-terminus readily react with W(CO)3(S2CNMe2)2 to replace the carbon monoxides and form the novel bis-alkyne complexes W(AA-CCH)2(S2CNMe2)2; the solution behavior of these complexes shows that only the alkyne, and not the other functional groups on the amino acid, bonds to the tungsten.     

Formally Renormalizable Gravitationally Self-Interacting String Models

It has recently been shown how the effect of thedivergent part of the gravitational self-interaction fora classical string model in four dimensions can beallowed for by a renormalization of its stress-energy tensor and in the elastic case a correspondingrenormalization of the off-shell action. It is shownhere that that it is possible to construct a newcategory of elastic string models for which this effect is describable as a renormalization in thestricter formal sense, meaning that itonly requires a rescaling of one of the fixed parameterscharacterizing the model.     

Carbon paste electrodes application to cathodic reductions and anodic stripping voltammetry

The utility of carbon paste electrodes for metal ion reductions and anodic stripping voltammetry is demonstrated. In addition certain organic reductions can be accomplished. Extension of the use of carbon electrodes to the cathodic range shows that this electrode has a wide range of potential applications. For anodic oxidations, the carbon paste electrode is perhaps the most versatile and useful stationary electrode available; it possesses practically zero anodic residual current and readily reproducible surfaces, and is simple to prepare and use. On the cathodic side carbon pastes arc limited by a non-removable residual current but this difficulty seems readily circumvented.     

Effects of ring strain on gas-phase rate constants. I. Ozone reactions with cycloalkenes

Rate constants for the gas-phase reactions of O₃ with a series of cycloalkenes and with cis-2-butene have been determined at 297 ± 1 K. The rate constants obtained were (in units of 10^?16 cm³/molecule·s): cis-2-butene, 1.38 ± 0.16; cyclopentene, 2.75 ± 0.33; cyclohexene, 1.04 ± 0.14; cycloheptene, 3.19 ± 0.36; 1,3-cyclohexadiene, 19.7 ± 2.8; 1,4-cyclohexadiene, 0.639 ± 0.074; bicyclo[2.2.1]-2-heptene, 21.4 ± 3.5; bicyclo[2.2.1]-2,5-heptadiene, 46.8 ± 12.9; and bicyclo[2.2.2]-2-octene, 0.728 ± 0.090. These data for cis-2-butene, cyclopentene, and cyclohexene are compared with previous literature data, and the effects of ring strain on the rate constants are discussed.     

Amidomethylation of indoles and cyclisations to spiro[pyrrolo[4,3,2-de]isoquinoline-3,4′-piperidines]

4-Aminomethylindoles react with aldehydes and ketones to form pyrrolo[4,3,2-de]isoquinolines. The structures of starting materials and end products were determined using 1D and 2D ¹H nmr techniques.