title: BiBr3-initiated tandem addition/silyl-Prins reactions to 2,6-disubstituted dihydropyrans.
abstract: A tandem addition/silyl-Prins reaction efficiently affords cis-2,6-disubstituted dihydropyrans (DHPs) using 5 mol % of BiBr3 in CH2Cl2. The reaction occurs between delta-triethylsilyloxyvinyltrimethylsilanes and a variety of aldehydes to give good to excellent isolated yields of DHPs. The diastereoselectivities in the crude products are significantly affected by aldehyde substitution with electron-rich aldehydes, providing 2-3:1 (cis:trans) and neutral (or electron-poor) aldehydes affording dr > or = 19:1 (cis:trans).
authors.affiliation: Department of Chemistry, College of William and Mary, P.O. Box 8795, Williamsburg, VA 23187-8795, USA.
authors.forename: Yajing
authors.initials: Y
authors.lastname: Lian
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Hinkle