We report herein a dynamic kinetic resolution (DKR) involving ortho-quinone methide (o-QM) intermediates. In the presence of Et N and the cinchonine-derived nucleophilic catalyst D, the DKR of 2-sulfonylalkyl phenols with allenic esters afforded chiral benzylic sulfones in 57-79 % yield with good to excellent enantioselectivity (85-95 % ee). Furthermore, with 2-(tosylmethyl)sesamols or 2-(tosylmethyl)naphthols, from which stable o-QM substrates can be generated, a formal [4+2] cycloaddition delivered 4-aryl- or alkyl-substituted chromans with excellent enantioselectivity (88-97 % ee).
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Enantioselective Reactions of 2-Sulfonylalkyl Phenols with Allenic Esters: Dynamic Kinetic Resolution and [4+2] Cycloaddition Involving ortho-Quinone Methide Intermediates.
Angew Chem Int Ed Engl
March 2017
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian, 116023, China.
We report herein a dynamic kinetic resolution (DKR) involving ortho-quinone methide (o-QM) intermediates. In the presence of Et N and the cinchonine-derived nucleophilic catalyst D, the DKR of 2-sulfonylalkyl phenols with allenic esters afforded chiral benzylic sulfones in 57-79 % yield with good to excellent enantioselectivity (85-95 % ee). Furthermore, with 2-(tosylmethyl)sesamols or 2-(tosylmethyl)naphthols, from which stable o-QM substrates can be generated, a formal [4+2] cycloaddition delivered 4-aryl- or alkyl-substituted chromans with excellent enantioselectivity (88-97 % ee).
View Article and Find Full Text PDFCatalytic asymmetric addition of Meldrum's acid, malononitrile, and 1,3-dicarbonyls to ortho-quinone methides generated in situ under basic conditions.
Chemistry
April 2015
Department of Industrial Chemistry "Toso Montanari", Alma Mater Studiorum-University of Bologna, V. Risorgimento 4, 40136 Bologna (Italy).
A new approach to the utilization of highly reactive and unstable ortho-quinone methides (o-QMs) in catalytic asymmetric settings is presented. The enantioselective reactions are catalysed by bifunctional organocatalysts, and the o-QM intermediates are formed in situ from 2-sulfonylalkyl phenols through base-promoted elimination of sulfinic acid. The use of mild Brønsted basic conditions for transiently generating o-QMs in catalytic asymmetric processes is unprecedented, and allows engaging productively in the reactions nucleophiles such as Meldrum's acid, malononitrile and 1,3-dicarbonyls.
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