Studies of the asymmetric [2+2] cycloaddition of silylketenes and aldehydes employing Ti-TADDOL catalysts
摘要:
Ti-TADDOL catalysts provide good reactivity and moderate enantioselectivity in the asymmetric [2+2] cycloaddition of silyl ketenes and aldehydes. The effects of potential bidentate chelation of benzyloxy substituted aldehydes and of the steric size of the ketene silyl group were studied. (C) 1998 Elsevier Science Ltd. All rights reserved.
Asymmetric [2 + 2] cycloaddition of ketene with the aldehydes 1aâg, catalysed by 10 mol% of C2-symmetric bissulfonamide 2aâcâR3Al complexes afforded optically active 4-substituted oxetan-2-ones 3aâg in up to 74% enantiomeric excess.
Catalytic Asymmetric Synthesis of trans-Configured β-Lactones: Cooperation of Lewis Acid and Ion Pair Catalysis
作者:Thomas Kull、José Cabrera、René Peters
DOI:10.1002/chem.201000840
日期:——
development of the first trans‐selective catalytic asymmetric [2+2] cyclocondensation of acyl halides with aliphatic aldehydes furnishing 3,4‐disubstituted β‐lactones is described. This work made use of a new strategy within the context of asymmetric dual activation catalysis: it combines the concepts of Lewisacid and organic aprotic ionpaircatalysis in a single catalyst system. The methodology could
Practical Enantioselective Synthesis of β-Lactones Catalyzed by Aluminum Bissulfonamide Complexes
作者:Thomas Kull、René Peters
DOI:10.1002/adsc.200700084
日期:2007.7.2
practical aluminum-bissulfonamide complex catalyzed enantioselective formation of β-lactones by [2+2] cycloaddition of ketene (generated in situ from acetyl bromide by dehydrobromination) with various α-unbranched and -branched aliphatic aldehydes is presented. The methodology offers the advantage of operational simplicity not only as the ligand synthesis requires just a single sulfonylation step from commercially
Cinchona Alkaloid-Lewis Acid Catalyst Systems for Enantioselective Ketene−Aldehyde Cycloadditions
作者:Cheng Zhu、Xiaoqiang Shen、Scott G. Nelson
DOI:10.1021/ja0492900
日期:2004.5.1
Asymmetric cinchona alkaloid-catalyzed acid chloride-aldehyde cyclocondensation (AAC) reactions afford enantioenriched 4-substituted and 3,4-disubstituted beta-lactones with near perfect absolute and relative stereocontrol. These reactions are characterized by the operational simplicity derived from using commercially available or easily obtained (one-step) reaction catalysts and in situ ketene generation from acid chlorides. The range of aldehyde substrates that serve as effective AAC substrates include sterically hindered aldehydes such as cyclohexanecarboxaldehyde and pivaldehyde.