title: Conformational preferences of oxy-substituents in butenolide-tetrahydropyran spiroacetals and butenolide-piperidine spiro-N,O-acetals.
abstract: We describe the synthesis of a series of oxy-substituted butenolide spiroacetals and spiro-N,O-acetals by oxidative spirocyclisation of 2-[(4-hydroxy or 4-sulfonamido)butyl]furans. The axial-equatorial preference of each oxy-substituent is investigated (NMR) by an acid-catalysed thermodynamic relay of configuration between the spiro- and oxy-centres. The axial site is preferred for most oxy-substituents at synthetically useful levels. The potential origins of this preference are discussed in terms of a stabilising gauche effect combined with the influence of solvation. These results have relevance to the synthesis of bis(acetylenic)enol ether spiroacetals including AL-1 and related compounds.
authors.affiliation: Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford, OX1 3TA, UK.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Naud
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Macnaughton
authors.forename: Bryony S
authors.initials: BS
authors.lastname: Dyson
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Woollaston
authors.forename: Jonathan W P
authors.initials: JW
authors.lastname: Dallimore
authors.forename: Jeremy
authors.initials: J
authors.lastname: Robertson