- Effect of chain length on radical to carbanion cyclo-coupling of bromoaryl alkyl-linked oxazolines: 1,3-Areneotropic migration of oxazolines
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(Chemical Equation Presented) 2-Halophenylalkyl-2-oxazolines with alkyl chain spacers of two to six C atoms (n = 0-4) were prepared and their S RN1-type reactions with several base systems examined. The best conditions to promote cyclocoupling to the corresponding benzocycloalkane derivatives involved use of LDA in THF. The precursors with 3-C-atom and 4-C-atom spacers gave good yields of 2-(1′-phenylindan-1′-yl)-2- oxazolines and 2-(1-phenyl-1,2,3,4-tetrahydronaphthalen-1-yl)-2-oxazoline, respectively. The major products from the precursor with a 5-C-atom spacer were derivatives of benzocycloheptane in which the oxazoline group had undergone a novel areneotropic migration from the end of the spacer to the benzo ring. The product from reaction of the corresponding 2-C-atom precursor was a 9-oxazolinophenanthrene derivative. EPR spectroscopy showed the intermediates of the LDA-promoted reactions to be radical anions of the product benzocycloalkanes. This supported an SRN1-type chain mechanism involving initial production of aryl radicals connected to azaenolate ions via the spacer groups. Intramolecular radical to carbanion coupling then generated ring-closed benzocycloalkane radical anions that transferred an electron to more precursor. Diastereoselective radical to carbanion cyclo-coupling reactions were carried out with 2-bromophenylpropyl precursors containing chiral 2-oxazolines. The diastereoselectivity achievable was modest, but the product diastereoisomeric Indane derivatives were easily separable by chromatography.
- Marshall, Laura J.,Roydhouse, Mark D.,Slawin, Alexandra M. Z.,Walton, John C.
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p. 898 - 911
(2007/10/03)
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- Diastereoselective conversion of sulfides into sulfoxides. 1,5- and 1,6-asymmetric induction
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The diastereoselective oxidation of sulfides into sulfoxides has been achieved with enantiomerically pure dihydrooxazole auxiliaries. When an additional hydroxymethyl substituent is present, diastereocontrol is very high and 1,5-asymmetric induction has been achieved with up to 96:4 selectivity, and 1,6-asymmetric induction has been achieved with up to 97:3 selectivity in the absence of any additional chiral agents.
- Bower, Justin F.,Martin, Christopher J.,Rawson, David J.,Slawin, Alexandra M. Z.,Williams, Jonathan M. J.
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p. 333 - 342
(2007/10/03)
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- Enantiomerically pure oxazolines tethered to alcohols. Preparation and use in asymmetric catalysis
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A series of enantiomerically pure oxazolines tethered to alcohols have been prepared. The use of these oxazolines has been demonstrated in the catalysed addition of diethylzine to aromatic aldehydes to afford the corresponding secondary alcohols with modest levels of asymmetric induction.
- Allen,Williams
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p. 277 - 282
(2007/10/02)
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