title: Rearrangement of 5-trimethylsilylthebaine on treatment with L-selectride: an efficient synthesis of (+)-bractazonine.
abstract: Treatment of 5-trimethylsilylthebaine with L-Selectride gave rise to a rearrangement to 10-trimethylsilylbractazonine through migration of the phenyl group, whereas treatment of thebaine with strong Lewis acids is known to lead to a similar rearrangement through migration of the alkyl bridge to give, after reduction, (+)-neodihydrothebaine. It is suggested that the rearrangement of the alkyl group of thebaine is favored due to the formation of a tertiary benzylic cation. However, for 5-trimethylsilylthebaine, the lithium ion of L-Selectride acts as the Lewis acid and the beta-silyl effect dominates in the stabilization of any positive charge. This rearrangement provides a clear example of the greater relative migratory aptitude of phenyl groups over alkyl groups, and provides an efficient synthesis of (+)-bractazonine from thebaine.
authors.affiliation: Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, 20 North Pine Street, Baltimore, Maryland 21201, USA.
authors.forename: Weibin
authors.initials: W
authors.lastname: Chen
authors.forename: Huifang
authors.initials: H
authors.lastname: Wu
authors.forename: Denzil
authors.initials: D
authors.lastname: Bernard
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Metcalf
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Deschamps
authors.forename: Judith L
authors.initials: JL
authors.lastname: Flippen-Anderson
authors.forename: Alexander D
authors.initials: AD
authors.lastname: MacKerell
authors.forename: Andrew
authors.initials: A
authors.lastname: Coop
mesh_terms: D000470:Alkaloids / Q000138:chemical synthesis / Q000737:chemistry; D002384:Catalysis; D020650:Combinatorial Chemistry Techniques; D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D013237:Stereoisomerism; D013797:Thebaine / Q000031:analogs & derivatives / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D000470:Alkaloids; D007202:Indicators and Reagents; C476081:bractazonine; D013797:Thebaine