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Synergistic Effect of Pybox Substituents and Lanthanide Cations in Reversing the Asymmetric Induction in the Catalysed Diels−Alder Reaction between 3‐Acryloyl‐1,3‐oxazolidin‐2‐one and Cyclopentadiene
Author(s) -
Desimoni Giovanni,
Faita Giuseppe,
Guala Matilde,
Laurenti Anna
Publication year - 2004
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200400160
Subject(s) - chemistry , cyclopentadiene , enantioselective synthesis , asymmetric induction , trifluoromethanesulfonate , lanthanide , substituent , ligand (biochemistry) , medicinal chemistry , selectivity , catalysis , diels–alder reaction , stereochemistry , chiral lewis acid , adduct , enantiomer , organic chemistry , ion , biochemistry , receptor
The enantioselectivity in the pybox/lanthanide( III ) triflate catalysed Diels−Alder reaction between cyclopentadiene and 3‐acryloyl‐1,3‐oxazolidin‐2‐one is profoundly influenced by the presence of a phenyl group in the 5′‐position of the ligand, since it sometimes amplifies, and sometimes reverses the enantioselectivity induced by the 4′‐substituent. The results can be summarised in three points. Of the catalysts derived from (4′ R ,5′ R )‐4‐Me‐5‐Ph‐pybox ( 6 ), the Sc III ‐based one is both strongly endo ‐selective and strongly enantioselective. Several catalysts derived from (4′ R ,5′ R )‐ trans ‐diphenyl‐pybox ( 9 ) give up to 50% yields of exo ‐ 4 and, at least with Pr III and La III , induce excellent ee values in both endo and exo adducts. The (4′ R ,5′ S )‐ cis ‐diphenyl‐pybox ( 8 ) is a novel and valuable ligand, since opposite enantiomers can be obtained with good selectivity simply by changing the cation from Sc III to La III . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)