title: Competitive silyl-Prins cyclization versus tandem Sakurai-Prins cyclization: an interesting substitution effect.
abstract: Two different mechanism pathways are observed for the reaction of allylsilyl alcohols 1 and aldehydes in the presence of trimethylsilyl trifluoromethanesulfonate (TMSOTf). In the case of allylsilyl alcohols without allylic substituents, the reaction gives dioxaspirodecanes, which are the products of a tandem Sakurai-Prins cyclization. In contrast, allylsilyl alcohols with an allylic substituent (R(2)≠H) selectively provide oxepanes, thus corresponding to a direct silyl-Prins cyclization. Both types of product are obtained with excellent stereoselectivity. Theoretical studies have been performed to obtain some rationalization for the observed stereoselectivity.
authors.affiliation: Department of Organic Chemistry, University of Valladolid, Campus Miguel Delibes, 47011 Valladolid (Spain), Fax: (+34) 983423013.
authors.forename: Alberto
authors.initials: A
authors.lastname: Diez-Varga
authors.forename: Héctor
authors.initials: H
authors.lastname: Barbero
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Pulido
authors.forename: Alfonso
authors.initials: A
authors.lastname: González-Ortega
authors.forename: Asunción
authors.initials: A
authors.lastname: Barbero
mesh_terms: D000438:Alcohols / Q000737:chemistry*; D000447:Aldehydes / Q000737:chemistry*; D000498:Allyl Compounds / Q000737:chemistry; D002384:Catalysis; D003500:Cyclization; D008698:Mesylates / Q000737:chemistry*; D013141:Spiro Compounds / Q000737:chemistry; D013237:Stereoisomerism; D014297:Trimethylsilyl Compounds / Q000737:chemistry*
chemical_list: D000438:Alcohols; D000447:Aldehydes; D000498:Allyl Compounds; D008698:Mesylates; D013141:Spiro Compounds; D014297:Trimethylsilyl Compounds; C053353:trimethylsilyl trifluoromethanesulfonate
keywords: allylation; cyclization; oxygen heterocycles; silanes; tandem catalysis