208037-81-4Relevant articles and documents
Cationic tropidinyl scandium catalyst: A perfectly acceptable substitute for cationic half-sandwich scandium catalysts in cis -1,4-Polymerization of isoprene and copolymerization with norbornene
Liu, Siqian,Du, Gaixia,He, Jianyun,Long, Yingyun,Zhang, Shaowen,Li, Xiaofang
, p. 3567 - 3573 (2014)
Different nonmetallocene rare earth metal alkyl complexes such as monotropidinyl (Trop) scandium dialkyl complex (Trop)Sc(CH2SiMe 3)2(THF) (1), ditropidinyl yttrium alkyl complex (Trop)2Y(CH2SiMe3)(THF) (3) as well as binuclear lutetium alkyl complex bearing one tetradentate dianionic 6-N-methyl-1,4-cycloheptadienyl (NMCH) ligand [(NMCH)Lu(CH2SiMe 3)(THF)]2 (2) have been synthesized in high yields via one-pot acid-base reaction by using of the tris(trimethylsilylmethyl) rare earth metal complexes with the readily available natural product tropidine. The polymerization experiments indicate that the monotropidinyl scandium dialkyl complex 1 displays reactivity akin to that of the analogous monocyclopentadienyl scandium dialkyl complexes. In the presence of activator and a small amount of AlMe3, complex 1 exhibits similar activities (up to 1.6 × 106 g molSc-1 h-1) but higher cis-1,4-selectivities (up to 100%) than (C5H5)Sc(CH 2SiMe3)2(THF) (cis-1,4-selectivity as 95%) in the isoprene polymerization, yielding the pure cis-1,4-PIPs with moderate molecular weights (Mn = 0.5-11.2 × 104 g/mol) and bimodal molecular weight distributions (Mw/Mn = 1.48-6.07). Moreover, the complex 1/[Ph3C][B(C6F 5)4/AliBu3 ternary system also shows good comonomer incorporation ability in the copolymerization of isoprene and norbornene similar to the [C5Me4(SiMe3)] Sc(η3-CH2CHCH2)2/activator binary system, affording the random isoprene/norbornene copolymers with a wide range of isoprene contents around 57-91 mol % containing cis-1,4 configuration up to 88%.
Enantiospecific Synthesis of Natural (-)-Cocaine and Unnatural (+)-Cocaine from D- And L-Glutamic Acid
Lin, Ronghui,Castells, Josep,Rapoport, Henry
, p. 4069 - 4078 (2007/10/03)
Natural (-)-cocaine and unnatural (+)-cocaine have been synthesized enantiospecifically from D-and L-glutamic acid, respectively. The axial-equatorial substitutents were introduced by a stereo-and regiospecific dipolar cycloaddition to the corresponding (1R,5S)- and (1S,5R)-N-BOC-nortropenes with (ethoxycarbonyl)formonitrile N-oxide. A sequence of subsequent stereochemically controlled transformations converted the fused isoxazoline to the requisite β-hydroxy ester. Synthesis of the key intermediate N-BOC-nortropenes involved construction of the 8-azabicyclo[3.2.1]octane framework by Dieckmann condensation of cis-5-substituted D- and L-proline esters. For comparison, (1R,5S)-N-BOC-nortropene also was derived by degradation from natural cocaine. The cis-5-substituted D- and L-proline esters were obtained by sulfide contraction and subsequent catalytic hydrogenation to induce stereospecifically the C-5 stereochemistry from D- and L-thiopyroglutamate, which in turn were prepared from D- and L-glutamic acids, respectively.
