Adsorption of Mono- and Divalent 4-(Dimethylamino)pyridines on Gold Surfaces: Studies by Surface-Enhanced Raman Scattering and Density Functional Theory.

The adsorption thermodynamics of 4-(dimethylamino)pyridine (DMAP) and its five divalent derivatives di-DMAP- n (2 ≤ n ≤ 6) with gradually increasing methylene-spacer lengths n binding to planar gold surfaces has been studied by surface-enhanced Raman spectroscopy (SERS) and density functional theory (DFT). SERS intensities of the totally symmetrical breathing mode of the pyridine ring at approximately 1007 cm are used to monitor the surface coverage of the DMAP and di-DMAP- n ligands on gold surfaces at different concentrations. The equilibrium constant as a measure of the binding affinity is obtained from these measurements by using a modified Langmuir isotherm.

Iodination of carbohydrate-derived 1,2-oxazines to enantiopure 5-iodo-3,6-dihydro-2-1,2-oxazines and subsequent palladium-catalyzed cross-coupling reactions.

Iodination of carbohydrate-derived 3,6-dihydro-2-1,2-oxazines of type using iodine and pyridine in DMF furnished 5-iodo-substituted 1,2-oxazine derivatives with high efficacy. The alkenyl iodide moiety of 1,2-oxazine derivatives - and - was subsequently exploited for the introduction of new functionalities at the C-5 position by applying palladium-catalyzed carbon-carbon bond-forming reactions such as Sonogashira, Heck, or Suzuki coupling reactions as well as a cyanation reaction. These cross-coupling reactions led to a series of 5-alkynyl-, 5-alkenyl-, 5-aryl- and 5-cyano-substituted 1,2-oxazine derivatives being of considerable interest for further synthetic elaborations.

Synthesis of 5-acetyloxazoles and 1,2-diketones from β-alkoxy-β-ketoenamides and their subsequent transformations.

Lithiated alkoxyallenes, nitriles, and carboxylic acids have been employed as precursors in a three-component reaction leading to highly substituted β-alkoxy-β-ketoenamides. Upon treatment with trifluoroacetic acid, these enamides could be easily cyclized to 5-acetyloxazole derivatives. The synthesis is very flexible with respect to the substitution pattern at C-2 and C-4 of the oxazole core.