New mannose-derived ketones as organocatalysts for enantioselective dioxirane-mediated epoxidation of arylalkenes. Part 3: Chiral ketones from sugars
New d-arabino-hexopyranosid-3-uloses were synthesized by a simple method from mannopyranoside derivatives. The common skeleton possesses a tunable alkoxy group as steric sensor on carbon 2 of the sugar. The new ketones were employed in the dioxirane-mediated epoxidation of a range of trans- and trisubstituted arylalkenes giving enantiomeric excesses from low to good (30-90%). The effect of the size of the steric sensor on the enantioselectivity was also studied. The least bulky group (methoxy group) enhanced the stereoselectivity (up to 90% ee toward triphenylethylene).
Vega-Pérez, José M.,Peri?án, Ignacio,Vega-Holm, Margarita,Palo-Nieto, Carlos,Iglesias-Guerra, Fernando
experimental part
p. 7057 - 7065
(2011/10/05)
Asymmetric counteranion-directed transition-metal catalysis: Enantioselective epoxidation of alkenes with Manganese(III) salen phosphate complexes
(Figure Presented) Figure Presentation Paired up: A highly active and enantioselective ion-pair epoxidation catalyst, consisting of an achiral Mn |||-salen complex and a chiral phosphate counteranion, mediates the epoxidization of a wide range of alkenes with high yields and enantioselectivities (see scheme). The unique role of the counteranion is to stabilize an enantiomorphic conformation of the cationic Mn catalyst.
Liao, Saihu,List, Benjamin
supporting information; experimental part
p. 628 - 631
(2010/04/06)
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