Enantioselective preparation of acetylenic or olefinic substituted cycloalkenyl dihydroxybutyrates and 4-hydroxy-tetrahydro-pyran-2-ones

A compound of formula I ##STR17## wherein X, X.sub.1 and X.sub.2 are independently H, F, Cl, Br, OH, CF.sub.3, alkyl, alkoxy, aryl, NO.sub.2, NH(CO)R, N(R).sub.2 or S(O).sub.m R;

• R.sub.1 and R.sub.2 are independently H, alkyl, aryl, OR, F, Cl or Br;
• R.sub.3 and R.sub.4 taken together can form a spirocyclic ring having 4 to 6 carbon atoms;
• R is H or lower alkyl;
• m is 0-2;
• and
• n is 0-2.