Highly Enantioselective Conjugate Addition of Thioglycolate to Chalcones Catalyzed by Lanthanum: Low Catalyst Loading and Remarkable Chiral Amplification
Ramping it up: The titled reaction has been developed using a chiral N,N′‐dioxide–LaIII complex as the catalyst. The reaction proceeded with high yield and enantioselectivity. Remarkably, a high asymmetric amplification was observed, as 98 % ee was achieved using 1 mol % L/La(OTf)3 in which the ee value of L was 2 % ee. Tf=trifluoromethanesulfonyl.
Asymmetric conjugate addition of thioglycolate to a range of chalcones using tetrahydroisoquinoline (TIQ) N,N′-dioxide ligands
作者:Sai Kumar Chakka、Zamani E.D. Cele、Sphelele C. Sosibo、Vivian Francis、Per I. Arvidsson、Hendrik G. Kruger、Glenn E.M. Maguire、Thavendran Govender
DOI:10.1016/j.tetasy.2012.04.010
日期:2012.4
A series of novel TIQ based N,N'-oxide ligands were synthesised and screened for their catalytic activity in the enantioselective conjugate addition of thioglycolate to chalcones. Bulky groups on the side chain of the TIQ backbone provided the highest enantioselectivity of up to 88% with 10 mol % catalyst loading. It was also observed that these reactions proceeded optimally in the presence of dichloromethane as a solvent. Screening of various metals emphasized La(OTf)(3) as the ideal pre-catalyst for this particular reaction. (C) 2012 Elsevier Ltd. All rights reserved.