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Paladhi, Sushovan,Liu, Yidong,Kumar, B. Senthil,Jung, Min-Jung,Park, Sang Yeon,Yan, Hailong,Song, Choong Eui THE AMERICAN CHEMICAL SOCIETY 2017 ORGANIC LETTERS Vol.19 No.12
<P>The potential of Song's chiral oligoethylene glycol's (oligoEGs) as catalysts was explored in the enantioselective protonation of trimethylsilyl enol ethers in combination with alkali metal fluoride (KF and CsF) and in the presence of a proton source Highly enantioselective protonatigns of various silyl enol ethers of alpha-substituted tetralohes were achieved, producing chiral alpha-substituted-Jetralones in full conversion and with up to 99% ee. The established protocol was successfully exiended to the synthesis of biologically relevant chiral alpha-substituted chromanone and thiothromarione derivatives.</P>
Paladhi, Sushovan,Park, Sang Yeon,Yang, Jung Woon,Song, Choong Eui THE AMERICAN CHEMICAL SOCIETY 2017 ORGANIC LETTERS Vol.19 No.19
<P>Biologically relevant chiral 3,3-disubstituted oxindole products containing a β-fluoroamine unit are obtained in high yields and with excellent stereoselectivity (up to 99% ee, dr >20:1 for <I>syn</I>) through the organocatalytic direct Mannich reaction of 3-fluoro-oxindoles as fluoroenolate precursors and α-amidosulfones as the bench-stable precursors of sensitive imines by using a chiral oligoethylene glycol and KF as a cation-binding catalyst and base, respectively. This protocol can be easily scaled without compromising the asymmetric induction. Furthermore, this protocol was also successfully extended to generate tetrasubstituted C–Cl and C–Br stereogenic centers.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/orlef7/2017/orlef7.2017.19.issue-19/acs.orglett.7b02628/production/images/medium/ol-2017-02628a_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ol7b02628'>ACS Electronic Supporting Info</A></P>
Paladhi, Sushovan,Hwang, In-Soo,Yoo, Eun Jeong,Ryu, Do Hyun,Song, Choong Eui American Chemical Society 2018 ORGANIC LETTERS Vol.20 No.7
<P>A practical and highly enantioselective nonenzymatic kinetic resolution of racemic β-hydroxy carbonyl (aldol) compounds through enantioselective dehydration process was developed using a cation-binding Song’s oligoethylene glycol (oligoEG) catalyst with potassium fluoride (KF) as base. A wide range of racemic aldols was resolved with extremely high selectivity factors (<I>s</I> = up to 2393) under mild reaction conditions. This protocol is easily scalable. It provides an alternative approach for the syntheses of diverse biologically and pharmaceutically relevant chiral aldols in enantiomerically pure form. For example, racemic gingerols could participate in this kinetic resolution with superb efficiency (<I>s</I> > 240), affording both enantiomerically pure gingerols and corresponding shogaols simultaneously in a single step. The dramatic effectiveness of such kinetic resolution process can be ascribed to systematic cooperative hydrogen-bonding catalysis in a densely confined supramolecular chiral cage in situ generated from the chiral catalyst, substrate, and KF.</P> [FIG OMISSION]</BR>
Min-Jung Jung,Sushovan Paladhi,송충의 대한화학회 2023 Bulletin of the Korean Chemical Society Vol.44 No.5
Herein, we report on the successful enantioselective protonation of a range of silyl enol ethers of cyclic ketones with labile chiral secondary C F bonds by using Song’s chiral oligoethylene glycols (oligoEGs) as cation-binding catalysts in the presence of CsF and a proton source. Highly enantioselective protonations of an array of silyl enol ethers of α-fluoro tetralones and α-fluoro benzosuberones were achieved, producing corresponding chiral α-secondary α-fluoro cyclic ketones in full conversion, with up to 96% ee. Furthermore, this protocol has successfully been extended to access chiral α-choro and α-bromo cyclic ketones. This successful in situ generated fluoride ion-based stereoselective catalysis was driven by creating a densely confined chiral cage from the chiral catalyst, substrate, and CsF.