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DOI: 10.1055/s-2008-1042724
NHC-Catalyzed Staudinger Reaction
Contributor(s):Benjamin List, Subhas Chandra PanInstitute of Chemistry, Chinese Academy of Sciences, Beijing, P. R. of China
Chiral N-Heterocyclic Carbene Catalyzed Staudinger Reaction of Ketenes with Imines: Highly Enantioselective Synthesis of N-Boc β-Lactams
Org. Lett. 2008, 10: 277-280
Publication History
Publication Date:
21 February 2008 (online)
Key words
Staudinger reaction - N-heterocyclic carbenes - β-lactams - enantioselectivity
Significance
A chiral N-heterocyclic carbene catalyzed Staudinger reaction of ketenes with N-Boc imines has been developed. Catalyst 1 in combination with Cs2CO3 has been found to be effective for this reaction. After investigating different N-protecting groups, N-Boc imines are found to be suitable for this reaction. With 10 mol% of triazolium salt 1, good to high yields (53-75%) and excellent enantioselectivities (er = 95:5 to >99:1) are obtained for a wide variety of ketenes and imines.
Comment
Catalytic asymmetric Staudinger reactions of ketenes with imines have been developed by the groups of Lectka (Acc. Chem. Res. 2004, 37, 592) and Fu (Acc. Chem. Res. 2004, 37, 542). However, N-Boc imines were not used in their processes. This method as developed by the present authors is highly useful for the synthesis of β-lactams because of the easy removal of the N-Boc protecting group.