title: Investigation of the asymmetric ionic Diels-Alder reaction for the synthesis of cis-decalins.
abstract: The ionic Diels-Alder reaction, whereby an alpha,beta-unsaturated acetal in combination with a Lewis or Bronsted acid forms an equilibrium concentration of an activated dienophile, has been developed to provide an enantioselective synthesis of cis-decalins. Cyclohex-2-enone type chiral acetals of (2R,3R)-butane-2,3-diol have been screened against Lewis and Brønsted acids with a variety of dienes and are efficient for the synthesis of a limited subset of cis-decalin structures. Diastereoselectivities of 73% and 82% have been found for the asymmetric ionic Diels-Alder reaction between the chiral acetal derivatives of cyclohex-2-enone (6) and 2-methylcyclohex-2-enone (18) with 2,3-dimethyl-1,3-butadiene (7). Terminal substituents on the diene partner in general render the system unreactive. However a synthetically useful cis-decalin 31, derived from the reaction of 2-methylcyclohex-2-enone and Z-3-t-butyldimethyl-silyloxypenta-1,3-diene has been prepared in enantiomerically pure form in 74% isolated yield using this asymmetric ionic Diels-Alder protocol.
authors.affiliation: School of Chemistry, University of Nottingham, Nottingham, UK NG7 2RD. j.anderson@nottingham.ac.uk
authors.forename: James C
authors.initials: JC
authors.lastname: Anderson
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Blake
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Graham
authors.forename: Claire
authors.initials: C
authors.lastname: Wilson