| 摘要 |
<p>A new enantioselective process is described for preparing optically active alpha-arylalkanoic acids by: a) halogenation on the aliphatic carbon atom alpha to the ketal group, of ketals of formula <CHEM> in which Ar represents an aryl, optically substituted; R represents a C1-C4 alkyl; R1 and R2, represent a hydroxy, a O<->M<+>, OR3 or NR4R5 group; the carbon atoms indicated by an asterisk both simultaneously are in (R) or (S) configuration. This reaction is diastereoselective, so that a misture of alpha-haloketals is obtained in which one of the two epimers prevails, and generally strongly prevails, over the other. b) rearrangement of the haloketals of formula <CHEM> in which X is Cl, Br or l to alpha-arylalkanoic acids in a single stage or in two successive stages, by way of esters of formula <CHEM> The compounds (A) and (C) are all new compounds. The rearrengement step (b) may be performed under new, inventive conditions. The esters of formula (C) have pharmacological activity analogous to that of the corresponding alpha-arylalkanoic acids.</p> |
