Deracemization of α-Aryl Hydrocoumarins via Catalytic Asymmetric Protonation of Ketene Dithioacetals
作者:Ji-Woong Lee、Benjamin List
DOI:10.1021/ja3096202
日期:2012.11.7
An unprecedented catalyticasymmetric protonation of ketene dithioacetals is described. Various racemic α-aryl hydrocoumarin derivatives are transformed into enantioenriched dithioacetal-protected hydrocoumarins in the presence of a chiral Brønsted acid catalyst. A newly developed phosphoric acid, featuring the 3,5-bis(pentafluorothio)phenyl (3,5-(SF(5))(2)C(6)H(3)) substituent, is introduced. The
α-Benzylation of (+)- and (−)-N-phenylacetyl imidazolidinones with 2-O-methoxy-methylbezyl bromides, followed by reductive removal of the chiral auxiliary and cyclization, afforded oxygenated isoflavans in excellent enantiomeric excess and yield.
作者:Jennifer M. Heemstra、Sean A. Kerrigan、Daniel R. Doerge、William G. Helferich、William A. Boulanger
DOI:10.1021/ol0620444
日期:2006.11.1
The first enantioselective totalsynthesis of (S)-equol is reported. The described route relies on an Evans alkylation to form the stereocenter and an intramolecular Buchwald etherification to generate the chroman ring. Key features of this method include its brevity, its scalability, and the low cost of starting materials. [reaction: see text].
Asymmetricaddition of arylboronicacids to 2H-chromenes proceeded in the presence of a hydroxorhodium/chiral diene catalyst to give 3-arylchromanes in high yields with high enantioselectivity. The reaction involves 1,4-Rh shift before protonation to release the addition product and to regenerate the hydroxorhodium species.