6-Chloro-2,3-dihydro-4H-1-benzopyran carboxylic acids: Synthesis, optical resolution and absolute configuration
摘要:
6-Chloro-2,3-dihydro-4H-1-benzopyran-2-carboxylic acid, a rigid analogue of clofibric acid, the active metabolite of the antilipidemic drug clofibrate, has been prepared together with two isomers, 6-chloro-2,3-dihydro-4H-1-benzopyran-3- and 4-carboxylic acids. The three acids have been resolved into their optical antipodes and the absolute configuration established by chemical correlation.
Access to racemic and enantioenriched 3-methyl-4-chromanones: catalysed asymmetric protonation of corresponding enolic species as the key step
摘要:
Bronsted acids induced the intramolecular cyclisation of 3-aryloxypropanoic esters affording 3-methyl-4-chromanones, which have been transformed into the corresponding racemic benzyl beta-oxoesters. These latter esters, in the presence of hydrogen and catalytic amounts of both palladium and (endo, endo) aminobomeol, led to optically active chromanones with up to 75% ee through a deprotection-decarboxylation-protonation cascade reaction. (C) 2003 Elsevier Ltd. All rights reserved.