1.Kinetic resolution of alpha-acetoxy carboxylic acids with homochiral SuperQuats.
Bew SP1, Davies SG, Fukuzawa SI. Chirality. 2000 Jun;12(5-6):483-7.
Preliminary investigations focused on the kinetic resolution of (+/-)-alpha-acetoxy mandelic carboxylic acid chloride with isopropyl SuperQuat and isopropyl Evans' homochiral auxiliaries. The addition of 2 equiv. of the acid chloride to the lithium salts of the auxiliaries (SuperQuat and Evans') at -100 degrees C in the THF afforded the corresponding N-acyl auxiliaries in high chemical yields (95% and 89%) and d.e.'s of 66% and 40%, respectively. Using the same mandelic acid chloride but incorporating SuperQuat auxiliaries derived from (S)-phenylglycine and (S)-phenylalanine yielded the corresponding N-acyl SuperQuats in 86% and 90% and d.e. 's of 66% and 30%, respectively. Substituting the phenyl group within the alpha-acetoxy mandelic acid chloride for a n-butyl, tert-butyl and cyclohexyl group changed the d.e. significantly when kinetically resolved with isopropyl SuperQuat. The yields were all similar, i.e., approximately 90% but the d.
2.SuperQuat N-acyl-5,5-dimethyloxazolidin-2-ones for the asymmetric synthesis of alpha-alkyl and beta-alkyl aldehydes.
Bull SD1, Davies SG, Nicholson RL, Sanganee HJ, Smith AD. Org Biomol Chem. 2003 Aug 21;1(16):2886-99.
The proclivity of alpha-branched N-2'-benzyl-3'-phenylpropionyl derivatives of (S)-4-benzyl-5,5-dimethyl-, (S)-4-phenyl-5,5-dimethyl-, (S)-4-isopropyl-5,5-dimethyl-, (S)-4-benzyl- and (S)-4-benzyl-5,5-diphenyl-oxazolidin-2-ones to generate directly 2-benzyl-3-phenylpropionaldehyde upon hydride reduction with DIBAL is investigated. The (S)-4-benzyl-5,5-dimethyl-derivative proved optimal for inhibition of endocyclic nucleophilic attack, giving 2-benzyl-3-phenylpropionaldehyde in good yield upon reduction. Application of this methodology for the asymmetric synthesis of chiral aldehydes via diastereoselective enolate alkylation of a range of (S)-N-acyl-4-benzyl-5,5-dimethyloxazolidin-2-ones to afford and array of alpha-substituted-N-acyl-5,5-dimethyloxazolidin- 2-ones (85-94% de) and subsequent reduction with DIBAL afforded directly non-racemic alpha-substituted aldehydes without loss of stereochemical integrity (87-94% ee). The extension of this protocol for the asymmetric synthesis of beta-substituted aldehydes is demonstrated, via the diastereoselective conjugate addition of a range of organocuprates to (S)-N-acyl-4-phenyl-5,5-dimethyloxazolidin-2-ones which proceeds with high diastereoselectivity (generally > 95% de).
