A mechanism study to identify the elements that control the chemoselectivity of metal-catalyzed N-atom transfer reactions of styryl azides is presented. Our studies show that the proclivity of the metal N-aryl nitrene to participate in sp-C-H bond amination or electrocyclization reactions can be controlled by either the substrate or the catalyst. Electrocyclization is favored for mono-β-substituted and sterically noncongested styryl azides, whereas sp-C-H bond amination through an H-atom abstraction-radical recombination mechanism is preferred when a tertiary allylic reaction center is present. Even when a weakened allylic C-H bond is present, our data suggest that the indole is still formed through an electrocyclization instead of a common allyl radical intermediate. The site selectivity of metal N-aryl nitrenes was found to be controlled by the choice of catalyst: Ir(I)-alkene complexes trigger electrocyclization processes while Fe(III) porphyrin complexes catalyze sp-C-H bond amination in substrates where Rh(II) carboxylate catalysts provide both products.

Dirhodium(II)-carboxylate complexes were discovered to promote the selective migration of acyl groups in trisubstituted styryl azides to form 1,2,3-trisubstituted indoles. The styryl azides are readily available in three steps from cyclobutanone and 2-iodoaniline.

A series of new highly soluble bispyrrolothiophenes were synthesized from vinyl azides by using transition-metal-catalyzed C-H-bond functionalization. In addition to modifying the substituents present on the end-pyrrolothiophene moieties, the arene linker in between the two units was also varied. The solution-state properties and field-effect-transistor (FET) electrical behavior of these bispyrrolothiophenes was compared. Our investigations identified that the optical properties and oxidation potential of our compounds were dominated by the pyrrolothiophene unit with a λmax  value of approximately 400 nm and oxidation at approximately 1 V. FET devices constructed with thin films of these bispyrrolothiophenes were also fabricated by means of thin-film solution processing. One of these compounds, a bispyrrolothiophene linked with benzothiodiazole, exhibits a mobility of approximately 0.3 cm(2)  V(-1)  s(-1) and the Ion/Ioff value is greater than 10(6).

SUMHARYOxygen-18 isotope labeled at the carboxyl group of glycine, L-alanine and L-proline were synthesized by acid catalyzed exchange or acid hydroll1;s of respective methyl ester derivatives of amino acids in HCl/H . Quantitative enrichment of ycine was achieved by the acid hydrofysis of amino fietonitrile in Hlf'O.In order to conserve the isotopic epfjichment [ 0) dipepti s were synthesized by solid phase method.[