Non-biaryl atropisomers derived from carbohydrates. Part 2. Atropisomeric behavior of monocyclic and bicyclic imidazolidine-2-ones and 2-thiones

High-yielding syntheses of bicyclic imidazolidine-2-ones and 2-thiones bear ing an ortho-substituted aromatic ring have been described. Their atropisom eric behavior has been studied in depth taking into account the effects of substituents in the ortho position, the length of the exocyclic C=X bond, a nd the presence of substituents at C-5 in the heterocyclic ring. The barrie rs to rotation were independently estimated by dynamic NMR spectroscopy and molecular mechanics. (C) 1999 Elsevier Science Ltd. All rights reserved.