Palladium-imidazolium carbene catalyzed Mizoroki-Heck coupling with aryl diazonium ions

[reaction: see text] Catalyst formed from N,N-bis(2,6-diisopropylphenyl)dihydroimidazolium chloride and palladium(II) acetate (2 mol %) was used, without added base, to efficiently produce Heck coupled products with olefins and aryl diazonium tetrafluoroborate substrates. The reactions were performed at room temperature, giving product in 2-4 h with 80-90% yields for isolated materials. Diazonium ions, formed in situ directly from anilines, also couple under these conditions.     

BOTPPI, a new Wittig salt for the synthesis of 12-(S)-hydroxy-eicosatetraenoic acid [12-(S)-HETE]

An efficient route to (Z)-(8-benzyloxy-8-oxooct-3-en-1-yl)triphenylphosphonium iodide, or BOTPPI, is disclosed, complete with full experimental details, NMR spectra, and HRMS data. BOTPPI serves as a surrogate for (Z)-(8-methoxy-8-oxooct-3-en-1-yl)triphenylphosphonium iodide, or MOTPPI, a Wittig salt previously used in two 12-HETE syntheses. BOTPPI has the advantage over MOTPPI of being derived from a sequence for which every intermediate is UV-active and amenable to large-scale chromatographic purification. A formal asymmetric total synthesis of 12-(S)-HETE is also reported, involving a stereoselective phase-transfer catalyzed (PTC) alkylation in its key step.     

Paradigms lost?

Thomas Kuhn (1957, 1962) explored the issues of paradigm shifts, scientific revolutions, and the relationship between them. Written before the techniques and practices of the complexity sciences were developed, Kuhn described what he termed the Copernican Revolution as the last scientific revolution signifying a paradigmatic shift in society. We will explore whether New Science approaches in nonlinear dynamics and complexity research signify postmodern science perspectives, and examine the role of New Science in what may be the on-going evolution of the next paradigm shift.     

Selective esterification of the polyphenol resveratrol at the 4′-position

Selective esterification of the polyphenol resveratrol was performed under thermodynamic conditions using NaH and acid anhydrides to directly access 4′-esters. Standard conditions with acetyl chloride and pyridine showed poor selectivity, favoring esterification at the 3-position. The extended 4′-phenolate anion is generated in preference to the 3-phenolate under the new anhydride-sodium hydride-DMSO conditions. Acylation occurs to access the 4′-ester products with modest selectivity and yield with minimal formation of the 3-monoester, 3,5-diester, and triester products.     

Ab initio treatment of the chemical reaction precursor complex Br(2P)-HCN. 2. Bound-state calculations and infrared spectra

Rovibronic energy levels and properties of the Br(2P)-HCN complex were obtained from three-dimensional calculations, with HCN kept linear and the CN bond frozen. All diabatic states that correlate to the 2P3/2 and 2P1/2 states of the Br atom were included and spin-orbit coupling was taken into account. The 3 x 3 matrix of diabatic potential surfaces was taken from the preceding paper (paper 1). In agreement with experiment, we found two linear isomers, Br-NCH and Br-HCN. The calculated binding energies are very similar: D0 = 352.4 cm(-1) and D0 = 349.1 cm(-1), respectively. We established, also in agreement with experiment, that the ground electronic state of Br-NCH has |Omega| = (1/2) and that Br-HCN has a ground state with |Omega| = (3/2), where the quantum number, Omega, is the projection of the total angular momentum, J, of the complex on the intermolecular axis R. This picture can be understood as being caused by the electrostatic interaction between the quadrupole of the Br(2P) atom and the dipole of HCN, combined with the very strong spin-orbit coupling in Br. We predicted the frequencies of the van der Waals modes of both isomers and found a direct Renner-Teller splitting of the bend mode in Br-HCN and a smaller, indirect, splitting in Br-NCH. The red shift of the CH stretch frequency in the complex, relative to free HCN, was calculated to be 1.98 cm(-1) for Br-NCH and 23.11 cm(-1) for Br-HCN, in good agreement with the values measured in helium nanodroplets. Finally, with the use of the same potential surfaces, we modeled the Cl(2P)-HCN complex and found that the experimentally observed linear Cl-NCH isomer is considerably more stable than the (not observed) Cl-HCN isomer. This was explained mainly as an effect of the substantially smaller spin-orbit coupling in Cl, relative to Br.