title: Stereoconvergent [1,2]- and [1,4]-Wittig rearrangements of 2-silyl-6-aryl-5,6-dihydropyrans: a tale of steric vs electronic regiocontrol of divergent pathways.
abstract: The regiodivergent ring contraction of diastereomeric 2-silyl-5,6-dihydro-6-aryl-(2H)-pyrans via [1,2]- and [1,4]-Wittig rearrangements to the corresponding α-silylcyclopentenols or (α-cyclopropyl)acylsilanes favor the [1,4]-pathway by ortho and para directing groups in the aromatic appendage and/or by sterically demanding silyl groups. The [1,2]-pathway is dominant with meta directing or electron-poor aromatic moieties. Exclusive [1,2]-Wittig rearrangements are observed when olefin substituents proximal to the silyl are present. cis and trans diastereomers exhibit different reactivities, but converge to a single [1,2]- or [1,4]-Wittig product with high diastereoselectivity and yield.
authors.forename: Luis M
authors.initials: LM
authors.lastname: Mori-Quiroz
authors.forename: Robert E
authors.initials: RE
authors.lastname: Maleczka
mesh_terms: D002384:Catalysis; D015394:Molecular Structure; D011714:Pyrans / Q000737:chemistry*; D012821:Silanes / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D011714:Pyrans; D012821:Silanes