title: 13C NMR analysis of 3,6-dihydro-2H-pyrans: assignment of remote stereochemistry using axial shielding effects.
abstract: The rational analysis of (13)C NMR axial shielding effects has enabled the assignment of remote relative stereochemistry in 3,6-oxygen-substituted 3,6-dihydro-2H-pyrans. Comparison of the (13)C NMR shifts of equivalent centers in cis- and trans-substituted 3,6-dihydro-2H-pyrans allows the relative configuration at the C3 and C6 positions to be defined in diastereoisomeric mixtures. Density functional calculations were used to validate this method and assess the conformational bias present in the ring system. Ultimately, the coupling of computational chemistry with this (13)C NMR-based method provided a reliable and convenient method for stereochemical assignment of a single diastereomer. This approach provides a facile and complementary alternative to the practices previously employed for determining the relative configuration in 3,6-dihydro-2H-pyrans.
authors.affiliation: School of Chemical and Physical Sciences, Victoria University of Wellington , P.O. Box 600, Wellington 6140, New Zealand.
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Bartlett
authors.forename: Peter T
authors.initials: PT
authors.lastname: Northcote
authors.forename: Matthias
authors.initials: M
authors.lastname: Lein
authors.forename: Joanne E
authors.initials: JE
authors.lastname: Harvey