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A Lewis Acid Promoted Asymmetric Umpolung Reaction with Chiral N ‐Sulfinyl Imines as the Electrophiles
Author(s) -
Xu Xin,
Liu Junying,
Chen Dianjun,
Timmons Cody,
Li Guigen
Publication year - 2005
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200400775
Subject(s) - umpolung , chemistry , electrophile , lewis acids and bases , absolute configuration , dithiane , stereochemistry , medicinal chemistry , organic chemistry , catalysis , nucleophile
An new asymmetric umpolung reaction has been developed by reacting N ‐sulfinyl imines with 2‐lithio‐2‐phenyl‐1,3‐dithiane. The reaction was conducted at between –20 and–25 °C in THF in the presence of Et 2 AlCl as the Lewis acid promoter. Excellent diastereoselectivities (up to >95 % de ) and chemical yields (64–95 %) have been achieved for nine substrates with all individual isomers separated and characterized. The absolute structure of the chiral products has been unambiguously determined by synthetic conversions to a known sample. 2‐Lithio‐2‐phenyl‐1,3‐dithiane was found to be much less reactive than its 2‐methyl counterpart, which was reported very recently. All individual isomers have been readily separated by column chromatography. The absolute structure of the chiral products has been unambiguously determined by conversion into a known compound. This method provides an easy access to enantiomerically pure α‐amino ketones. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)