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ABSTRACT:Procyanidins are important biologically active compounds, but the pathway and extent of absorption and metabolism are controversial. We conducted a mass balance study to evaluate the total radioactivity excreted in urine and feces after oral administration of

The single coordination-site transition metal Lewis acids [CpM(BIPHOP-F)][SbF6] (M = Fe, Ru) catalyze the [3+2] dipolar cycloaddition reaction between reactive nitrones and alpha,beta-unsaturated aldehydes to give chiral isoxazolidines with ee values of 75 to >96%. The stereochemistry of the major enantiomer is consistent with an endo approach of the nitrone to the Calpha-Si-face of the enal in the s-trans conformation in the (R,R)-catalyst site. The absolute configuration is based on an X-ray structure determination.

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Abstract:The C2-symmetric electron-poor ligand (R)-BINOP-F (4) was prepared by reaction of (R) Moreover, a second exchange process renders the diastereotopic BINOP-F phosphorus atoms equivalent. These processes were studied by the application of variable-temperature 1 H, 31 P, and 17 O NMR spectroscopy, variable-pressure 31 P and 17 O NMR spectroscopy, and, using a simpler model complex, density functional theory (DFT) calculations. The results point to a dissociative mechanism of the aquo ligand and a pendular motion of the BINOP-F ligand. NMR experiments show an energy barrier of 50.7 kJ mol -1 (12.2 kcal mol -1 ) for the inversion of the pseudo-chirality at the ruthenium center.-