Browsing by Author "Garner, A. Christopher"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Kinetic resolution and parallel kinetic resolution of methyl (±)-5-alkyl-cyclopentene-1-carboxylates for the asymmetric synthesis of 5-alkyl-cispentacin derivatives
    (2005) Davies, Stephen G.; Garner, A. Christopher; Long, Marcus J. C.; Morrison, Rachel M.; Roberts, Paul M.; Savory, Edward D.; Smith, Andrew D.; Sweet, Miles J.; Withey, Jonathan M.
    Conjugate addition of lithium dibenzylamide to methyl 5-isopropyl, 5-phenyl- and 5-tert-butyl-cyclopentene-1-carboxylates occurs with high levels of substrate control (>88% de), with preferential addition to the face of the cyclic α,β-unsaturated acceptor anti- to the stereodirecting 5-alkyl substituent. Treatment of a range of methyl (±)-5-alkyl-cyclopentene-1-carboxylates with both lithium (±)-N-benzyl-N-α-methylbenzylamide and lithium (±)-N-3,4-dimethoxybenzyl-N-α-methylbenzylamide indicates significant enantiorecognition in their mutual kinetic resolutions, with preferential addition anti- to the 5-alkyl substituent, giving the 1,2-syn-1,5-anti-arrangement (E >16) after enolate protonation anti- to the amino functionality. The kinetic resolution of a range of methyl (±)-5-alkyl-cyclopentene-1-carboxylates with lithium (S)-N-benzyl-N-α-methylbenzylamide, and their efficient parallel kinetic resolution with a pseudoenantiomeric mixture of lithium (S)-N-benzyl-N-α-methylbenzylamide and lithium (R)-N-3,4-dimethoxybenzyl-N-α-methylbenzylamide are also demonstrated, giving a range of 5-alkyl-cispentacin derivatives in >98% de and high ee after N-deprotection.
  • Thumbnail Image
    Item
    Parallel kinetic resolution of tert-butyl (RS)-3-alkyl–cyclopentene-1-carboxylates for the asymmetric synthesis of 3-alkyl–cispentacin derivatives
    (2004) Davies, Stephen G.; Garner, A. Christopher; Long, Marcus J. C.; Smith, Andrew D.; Sweet, Miles J.; Withey, Jonathan M.
    The double mutual kinetic resolution of tert-butyl (RS)-3-benzyl-cyclopentene-1-carboxylate with a 50 : 50 mixture of lithium (RS)-N-benzyl-N-alpha-methylbenzylamide and lithium (RS)-N-3,4-dimethoxybenzyl-N-alpha-methylbenzylamide gives, after protonation with 2,6-di-tert-butylphenol, a 50 : 50 mixture of the readily separable N-benzyl-(1SR,2RS,3RS,alphaRS)- and N-3,4-dimethoxybenzyl-(1SR,2RS,3RS,alphaRS)-beta-amino esters in >98% de in each case. This product distribution indicates that these amides react at very similar rates and with no mutual interference to furnish readily separable products, and are thus ideal for parallel kinetic resolution. The efficient parallel kinetic resolution ( E > 65) of a range of tert-butyl (RS)-3-alkyl-cyclopentene-1-carboxylates with a pseudoenantiomeric mixture of homochiral lithium (S)-N-benzyl-N-alpha-methylbenzylamide and lithium (R)-N-3,4-dimethoxybenzyl-N-alpha-methylbenzylamide gives, after separation and N-deprotection, a range of carboxylate protected 3-alkyl-cispentacin derivatives in >98% de and >95% ee.
  • Thumbnail Image
    Item
    Preparation of methyl (1R,2S,5S)- and (1S,2R,5R)-2-amino-5-tert-butyl-cyclopentane-1-carboxylates by parallel kinetic resolution of methyl (RS)-5-tert-butyl-cyclopentene-1-carboxylate
    (2003) Davies, Stephen G.; Díez, David; El Hammouni, Mohamed M.; Garner, A. Christopher; Garrido, Narciso M. ; Long, Marcus J. C.; Morrison, Rachel M.; Smith, Andrew D.; Sweet, Miles J.; Withey, Jonathan M.
    Comparison of the kinetic and parallel kinetic resolutions of methyl (RS)-5-tert-butyl-cyclopentene-1-carboxylate allows for the efficient synthesis of both (1R,2S,5S)- and (1S,2R,5R)-enantiomers of methyl 2-amino-5-tert-butyl-cyclopentane-1-carboxylate.