title: Tuning the reactivity of oxygen/sulfur by acidity of the catalyst in Prins cyclization: oxa- versus thia-selectivity.
abstract: An unprecedented oxa- versus thia-selectivity has been observed in Prins cyclization of 6-mercaptohex-3-en-1-ol with aldehydes. In the presence of a stoichiometric amount of strong Lewis or Brønsted acids, the reaction provides the hexahydro-2H-thieno[3,2-c]pyran skeleton predominantly via oxonium-Prins cyclization. In contrast, a catalytic amount of weak Lewis or Brønsted acids provides the hexahydro-2H-thiopyrano[4,3-b]furan preferentially through thionium-Prins cyclization.
authors.affiliation: Natural Product Chemistry and ‡Laboratory of X-ray Crystallography, Indian Institute of Chemical Technology , Hyderabad 500 007, India.
authors.forename: B V Subba
authors.initials: BV
authors.lastname: Reddy
authors.forename: A
authors.initials: A
authors.lastname: Venkateswarlu
authors.forename: Prashant
authors.initials: P
authors.lastname: Borkar
authors.forename: J S
authors.initials: JS
authors.lastname: Yadav
authors.forename: B
authors.initials: B
authors.lastname: Sridhar
authors.forename: René
authors.initials: R
authors.lastname: Grée