<i>C</i><i><sub>2</sub></i>-Symmetric Tin(II) Complexes as Chiral Lewis Acids. Catalytic Enantioselective <i>Anti</i> Aldol Additions of Enolsilanes to Glyoxylate and Pyruvate Esters
作者:David A. Evans、David W. C. MacMillan、Kevin R. Campos
DOI:10.1021/ja972547s
日期:1997.11.1
important role in the design of Sn(II)-based chiral Lewisacidiccomplexes. Specifically, the Lewisacidiccomplexes 1 and 2 derived from Sn(OTf)2 and bidentate bis(oxazoline)4 and tridentate pyridylbis(oxazoline)5 ligands6 are efficient anti-aldol catalysts for the enantioselective addition of enolsilanes to 1,2-dicarbonyl compounds. These ligand-metal complexes exhibit efficient turnover in the catalytic
Optically active tricarbonyl[.eta.6-o-(trimethylsilyl)benzaldehyde]chromium(0) complexes in organic synthesis: a highly anti-selective asymmetric aldol reaction with O-silyl ketene O,S-acetals
Treatment of optically pure (+)-tricarbonyl[o-(trimethylsilyl)benzaldehyde]chromium(0), (+)-1, with O-silyl ketene O,S-acetals 4c-f afforded, after decomplexation, the (-)-anti-aldol products (-)-5c-f, while an antipode, (-)-1, provided the (+)-anti ones (+)-5c-f. Optical purity of these aldol products were determined to be in a range of 92 to > 98% ee. The absolute configuration was established by an X-ray crystallographic analysis.
A Catalyst Designed for the Enantioselective Construction of Methyl- and Alkyl-Substituted Tertiary Stereocenters
作者:Aurélie Claraz、Gokarneswar Sahoo、Dénes Berta、Ádám Madarász、Imre Pápai、Petri M. Pihko
DOI:10.1002/anie.201509302
日期:2016.1.11
identifying substituent effects on enantioselectivity, was designed. The catalytic process allows rapid access to chiral thioesters, amides, aldehydes, and ketones bearing an α‐methyl stereocenter with excellent enantioselectivities, and allowed rapid access to the C4–C13 segment of (−)‐bistramide A. DFT calculations rationalized the observed sense and level of enantioselectivity.