Odd R. Gautun

X-ray scattering from oriented poly(3-alkylthiophenes)

Abstract Solution-cast films of poly(3-hexylthiophene) (P3HT) and poly(3-octylthiophene) (P3OT) were oriented by stretching to obtain more detailed information about their crystalline structure. For the first time reflections associated with the stretch direction l = 1–7 were revealed using a combination of X-ray film exposures and detailed intensity mapping by various detector scans. The reflections were located at finite angles to the stretch axis indicating a monoclinic (or triclinic) unit cell. The equatorial diffraction patterns (l = 0) of P3HT and P3OT show that the two structures are equal only with one differing lattice dimension caused by the length of the alkyl side chains. The crystalline structure for the unstretched (isotropic) and the stretched sample is found to be the sa me. Existence of h00 and absence of hk0, h0l and hkl reflections, all with finite integers h, k and l, indicate layer stacking disorder between bc-planes. Intensity calculations based upon this model corroborate well with the measured diffraction pattern on the assumption of disordered alkyl side chains.

Chain configuration of poly(3-hexylthiophene) as revealed by detailed X-ray diffraction studies

Abstract Detailed diffractometer and Laue x-ray studies of streched poly (3-hexylthiophene) films enabled us to identify several 001 reflections associated with the polymer chain direction. The chain repetition distance could then be determined for the first time, giving c =2·7.4 A =14.8 A . 7.4 A is shorter than expected for a model involving “alternating updown” monomers along the chain (7.8A), whereas the observed c value is in agreement with a new “up-up-down-down” model (14.9A). Intensity calculations assuming side chain disorder corroborate well with the new model.

Chiral Hetero‐ and Carbocyclic Compounds from the Asymmetric Hydrogenation of Cyclic Alkenes

Several types of chiral hetero- and carbocyclic compounds have been synthesized by using the asymmetric hydrogenation of cyclic alkenes. N,P-Ligated iridium catalysts reduced six-membered cyclic alkenes with various substituents and heterofunctionality in good to excellent enantioselectivity, whereas the reduction of five-membered cyclic alkenes was generally less selective, giving modest enantiomeric excesses. The stereoselectivity of the hydrogenation depended more strongly on the substrate structure for the five- rather than the six-membered cyclic alkenes. The major enantiomer formed in the reduction of six-membered alkenes could be predicted from a selectivity model and isomeric alkenes had complementary enantioselectivity, giving opposite optical isomers upon hydrogenation. The utility of the reaction was demonstrated by using it as a key step in the preparation of chiral 1,3-cis-cyclohexane carboxylates.

Crystal structures of two furanosesquiterpenes from Commiphora sphaerocarpa

The relative stereochemistry of a furanosesquiterpene, reported previously from myrrh, but isolated here from Commiphora sphaerocarpa is determined for the first time as (1(10)E,2R*,4R*)-2-methoxy-8,12-epoxygermacra-1(10),7,11-trien-6-one. Likewise the stereochemistry of furanodienone was established by NMR and X-ray crystallography as (1(10)E,4E)-8,12-epoxygermacra-1(10),4,7,11-tetraen-6-one.

Molecular structure of stretch oriented poly(3-hexylthiophene) studied by an extended X-ray diffraction mapping

Abstract Detailed x-ray diffraction intensity mapping of the reciprocal space of stretched poly(3-hexylthiophene) films enabled us for the first time to reveal reflections associated with the stretch direction (l = 1−7). The reflections are located at finite angles to the stretch axis and can therefore only be indexed on a monoclinic (or triclinic) unit cell. The monoclinic cell parameters are a =16.90 A , b =4.85 A , c =7.84 A , α=50.6° , ( a =4.85 A , b =16.90 A , c =7.84 A and β=129.4° by crystallographic conventions) and with two monomer units per cell. The values of a and c are directly measured whereas b and α are refined from structure factor calculations. Existence of h00 but absence of hk0, h0l and hkl reflections indicate layer disorder between oblique bc planes, whereas structure factor calculations indicate side chain disorder.

Asymmetric N-sulfinyl dienophile Diels–Alder cycloadditions using chiral Ti(IV)-based Lewis acids

Enantioselective Diels–Alder reactions of 1,3-cyclohexadiene with N-sulfinylbenzyl carbamate (1a) or N-sulfinyl-p-toluenesulfonamide (1b) promoted by chiral Ti(IV)-based Lewis acids are reported. The endo-adducts were obtained in 15–76% ee.

Asymmetric Diels–Alder reactions of N-sulfinyl dienophiles using chiral Ti(IV) Lewis acids

Abstract Enantioselective hetero Diels–Alder (HDA) reactions of 1,3-cyclohexadiene with benzyl N-sulfinylcarbamate 1a and with N-sulfinyl-p-toluensulfonamide 1b promoted by chiral Ti(IV)-based Lewis acids are reported. The obtained yields and enantiomeric excesses obtained are heavily dependant on the mode of catalyst preparation. Acceptable reproducibility was obtained with Ti(IV)-catalysts prepared from Me2TiCl2 and chiral diols. Testing of various chiral diols gave the endo adduct in yields of up to 69% with 76% ee. The absolute configuration of the HDA products were established by chemical correlation and verified by X-ray crystallography.

Highly enantioselective hetero Diels–Alder reactions of N-sulfinyl dienophiles promoted by copper(II)- and zinc(II)-chiral bis(oxazoline) complexes

Abstract Hetero Diels–Alder reactions of 1,3-cyclohexadiene with N -sulfinyl dienophiles 1a or 1b , promoted by Cu(II)- or Zn(II)-chiral bis(oxazoline) complexes, afforded endo adducts in high yields (up to 85%) and enantiomeric excess (e.e. of up to >98%) under stoichiometric conditions. With 10 mol% loading of the Zn(II) catalyst up to 75% e.e. was obtained for the endo adduct ( endo : exo =10:1, total yield 68%).

Regioselectivity in the Thermal Rearrangement of Unsymmetrical 4-Methyl-4H-1,2,4-triazoles to 1-Methyl-1H-1,2,4-triazoles

The rearrangement of 4-methyl-3,5-diaryl-4H-1,2,4-triazoles to the corresponding 1-methyl-3,5-diaryl-1H-1,2,4-triazoles showed regioselectivity comparable to that observed for the alkylation of 3,5-diaryl-1H-1,2,4-triazoles. This lends support to a proposed mechanism for the rearrangement that involves consecutive nucleophilic displacements steps.

Two octanordammarane triterpenes from Commiphora kua

The resin of Commiphora kwo yielded two new octanordammarane triterpenes namely 15 alpha-hydroxymansumbinone and 28-acetoxy-15 alpha-hydroxymansumbinone, along with the four known compounds, mansumbinone, mansumbinol, (16S, 20R)-dihydroxydammar-24-en-3-one and T-cadinol. These structures were elucidated by spectroscopic techniques, including 1D and 2D NMR spectroscopy, and X-ray analysis.