摘要:
A method for the preparation of a compound of formula ##STR1## wherein R is hydrogen or, respectively, a group of formula ##STR2## R.sub.1 is alkyl; Ar is optionally substituted aryl; and R.sub.3' and R.sub.3" are hydrogen, alkyl or phenyl, or R.sub.3' and R.sub.3" taken together with the carbon atom to which they are attached form cycloalkyl, or salt thereof, comprising acid facilitated acetalizing or ketalizing of a compound of formula ##STR3## wherein R.sub.3' and R.sub.3" are as defined above, and R.sub.4' and R.sub.4" are alkoxy, or taken together with the carbon atom to which they are attached form carbonyl, with a compound of formula ##STR4## wherein * represents an R chirality; R, R.sub.1 and Ar are as defined above, or salt thereof in isopropanol.