Key features of the β-isocupreidine (β-ICD)-catalyzed asymmetric Baylis–Hillmanreaction of aldehydes with 1,1,1,3,3,3-hexafluoroisopropyl acrylate (HFIPA) are presented. In addition, an improved method using azeotropically dried β-ICD is described.
presence of CCl4. Under similar conditions quinidine acetate 1b and epiquinidine acetate 2b dihydrochlorides both yield 10,10-difluoro derivatives epimeric at C-3, 6 and 7, and 9c and 10b, and a rearranged difluoro derivative 8b and 11b, respectively. Epiquinidine 2a leads to the expected analogues 10a and 11a and to a ketone 9a. Formation of gem-difluoro compounds implies chloro intermediates at C-10
In HF-SbF5, with or without H2O2, a source of 'OH+ equivalent, quinidine la yields three ethers, the preferred conformation of the substrate favoring the observed cyclization. Under similar conditions, quinidine acetate 1b, epiquinidine 2a, and its acetate 2b give fluorhydrins with or without rearrangement in different amounts according to the nature of the substrate and the acidity. At low acidity, epiquinidine 2a yields selectively a sole nonrearranged fluorhydrin 10a. Quinidine acetate 1b, at high acidity, yields only rearranged fluorhydrins 8b and 9b. (c) 2006 Elsevier Ltd. All rights reserved.