title: A New Strategy for the Synthesis of alpha-Difluoromethyl-Substituted alpha-Hydroxy and alpha-Amino Acids.
abstract: A new method for the preparation of alpha-chlorodifluoromethyl-, alpha-bromodifluoromethyl-, and alpha-difluoromethyl-substituted alpha-hydroxy and alpha-amino acid esters 11, 19-21 is described. The key step of the synthesis is the regioselective alkylation of ketones 5, 7-9 and imines 16-18 with C-nucleophiles. The ketones 7-9 are readily available from 3,3,3-trifluorolactate 1 by a five-step procedure. Subsequent removal of the protecting groups from 19-21 provides the corresponding free amino acids 25, 26, 28.
authors.affiliation: A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilov str. 28, GSP-1, V-334, RUS-117813 Moscow, Russia, and Institute of Organic Chemistry, University of Leipzig, Talstrasse 35, D-04103 Leipzig, Germany.
authors.forename: Sergey N.
authors.initials: SN
authors.lastname: Osipov
authors.forename: Alexander S.
authors.initials: AS
authors.lastname: Golubev
authors.forename: Norbert
authors.initials: N
authors.lastname: Sewald
authors.forename: Thomas
authors.initials: T
authors.lastname: Michel
authors.forename: Alexey F.
authors.initials: AF
authors.lastname: Kolomiets
authors.forename: Alexander V.
authors.initials: AV
authors.lastname: Fokin
authors.forename: Klaus
authors.initials: K
authors.lastname: Burger