75925-37-0Relevant academic research and scientific papers
Attribution de la configuration des orthobiphenyl-1 phenyl-1 methyl-2 ethylenes par resonance magnetique nucleaire du carbone-13. Synthese stereospecifique de l'isomere Z.
Nourmamode, Aziz,Lapouyade, Rene,Barbe, Bernard,Petraud, Michel
, p. 207 - 213 (2007/10/02)
Orthovinylbiphenyls are efficiently photocyclized to 9,10-dihydrophenantrenes which are of interest in their own right and as precursors of phenantrenes.Since we had previously determined the stereoselectivity of the cyclization of orthovinylbiphenyls while investigating the nature of the reactive state we found it useful to have available a straightforward method for assigning the configurations of these compounds.The method of Pascual and Tobey for evaluating the chemical shift of an olefinic proton have been tentatively applied to assign the Z and E configurations of 1-orthobiphenyl-1-phenyl-2-methylethylenes.The values calculated empirically, from model compounds, of the differential shielding between olefinic protons in both Z and E configurations are too close to be useful for assignment of the experimental values to specific configurations.By way of contrast a carbon-13 nuclear magnetic resonance study of model compounds such as 1,1,-diphenylethylene, 1-ortho-biphenyl-1-phenylethylene, and the 2-methylated compounds allows the assignment of configurations E and Z for the two isomers of 1-orthobiphenyl-1-phenyl-2-methylethylene since the methyl has a positive contribution to the chemical shift of the trans quaternary aromatic carbon and a negative one of the same amplitude for the cis quaternary aromatic carbon (γ effect).The assignment of 13C NMR signals of the olefinic carbons and of the quaternary aromatic carbons have been carried out from residual splitting of long-range 13C-1H coupling constants obtained by off-resonance irradiation.Specifically continuous wave irradiation at 8.66 ppm with a field γH2/2? ca. 350 Hz selectively decouples aromatic protons, and one can observe reduced splittings due to olefinic and aliphatic hydrogens.Assuming that 3Jtrans (13C-1H) > 3Jcis (13C-1H), the assignment of the quaternary aromatic carbon atom follows and makes it possible to measure the γ effect of the methyl group.To corroborate the assignment of configuration of 1-orthobiphenyl-1-phenyl-2-methylethylene we have performed a six step stereospecific synthesis of the Z isomer which takes advantage of the preferred syn addition of HBr to a triple bond in presence of HgBr2 and of the substitution with retention of an olefinic bromine by the phenyl gruoup of Ph2CuLi.
Divergent Stereochemistry of Photocyclization from Singlet and Triplet States of 2-Vinylbiphenyls. X-Ray Crystal Structure of cis-9-Phenyl-10-methyl-9,10-dihydrophenanthrene
Lapouyade, Rene,Koussini, Rafik,Nourmamode, Aziz,Courseille, Christian
, p. 740 - 742 (2007/10/02)
The singlet cyclization of Z(or E)-1-biphenyl-2-yl-1-phenylpropene proceeds stereoselectively to cis (or trans)-9-phenyl-10-methyl-9,10-dihydrophenanthrene (the cis-isomer has been characterized by X-ray crystallopgraphy) while the triplet cyclization gives a / ratio of 9:1 whatever the starting isomer.
