title: Tetrahydropyran rings from a Mukaiyama-Michael cascade reaction.
abstract: A new annulation reaction leading to tetrahydropyrans has been discovered. The reaction of homoallylic enol ethers (e.g., 1) with alpha,beta-unsaturated ketones or esters begins with a Mukaiyama-Michael addition. The intermediate oxocarbenium ion undergoes a rapid 2-oxonia-Cope rearrangement, and the resulting zwitterion collapses to form a tetrahydropyran. The reaction is stereoselective with 3-butene-2-one, but leads to diastereomeric mixtures with ethyl acrylate. More complex enones, such as cyclohexenone, also undergo the reaction to produce fused ring products. The optical activity of the substrates is relayed in the tetrahydropyran products.
authors.affiliation: Department of Chemistry, University of California, Irvine, Irvine, California 92697-2025, USA.
authors.forename: Megan L
authors.initials: ML
authors.lastname: Bolla
authors.forename: Brian
authors.initials: B
authors.lastname: Patterson
authors.forename: Scott D
authors.initials: SD
authors.lastname: Rychnovsky
mesh_terms: D000179:Acrylates / Q000737:chemistry; D000475:Alkenes / Q000737:chemistry*; D002074:Butanones / Q000737:chemistry; D003500:Cyclization; D015394:Molecular Structure; D011714:Pyrans / Q000737:chemistry*
chemical_list: D000179:Acrylates; D000475:Alkenes; D002074:Butanones; D011714:Pyrans; C040833:ethyl acrylate; C057920:3-buten-2-one; C013658:propylene