title: Allylic and allenic halide synthesis via NbCl(5)- and NbBr(5)-mediated alkoxide rearrangements.
abstract: Addition of NbCl(5) or NbBr(5) to a series of magnesium, lithium, or potassium allylic or propargylic alkoxides directly provides allylic or allenic halides. Halogenation formally occurs through a metalla-halo-[3,3] rearrangement, although concerted, ionic, and direct displacement mechanisms appear to operate competitively. Transposition of the olefin is equally effective for allylic alkoxides prepared by nucleophilic addition, deprotonation, or reduction. Experimentally, the niobium pentahalide halogenations are rapid, afford essentially pure (E)-allylic or -allenic halides after extraction, and are applicable to a range of aliphatic and aromatic alcohols, aldehydes, and ketones.
authors.affiliation: Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, Pennsylvania 15282-1530, USA.
authors.forename: P C
authors.initials: PC
authors.lastname: Ravikumar
authors.forename: Lihua
authors.initials: L
authors.lastname: Yao
authors.forename: Fraser F
authors.initials: FF
authors.lastname: Fleming
mesh_terms: D000438:Alcohols / Q000737:chemistry*; D000447:Aldehydes / Q000737:chemistry*; D001965:Bromides / Q000737:chemistry*; D002712:Chlorides / Q000737:chemistry*; D006846:Hydrocarbons, Halogenated / Q000138:chemical synthesis* / Q000737:chemistry; D007659:Ketones / Q000737:chemistry*; D015394:Molecular Structure; D009556:Niobium / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: D000438:Alcohols; D000447:Aldehydes; D001965:Bromides; D002712:Chlorides; D006846:Hydrocarbons, Halogenated; D007659:Ketones; D009942:Organometallic Compounds; C545369:niobium pentabromide; D009556:Niobium; C535111:niobium pentachloride