Process for preparing spiro derivatives

A process for preparing a compound of the formula ##STR6## wherein R is a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group;

• R.sub.1 and R.sub.2, which may be the same or different, represent a hydrogen atom an alkyl group or together with the nitrogen atom to which they are attached form a nitrogen-containing 5- or 6-membered heterocyclic ring in which the remaining atoms of said ring are carbon atoms;
• A represents a >CH.sub.2 group or a >C.dbd.O group;
• and n is 4 or 5, comprising;
• (1) treating .beta.-hydroxyacid of the general formula (II):
• ##STR7## wherein R and n have the same significance as in the general formula (I), with a strong acid;
• (2) hydrolyzing the product of step (1) to form a .gamma.-spirolactone of the general formula (III):
• ##STR8## wherein R and n have the same significance as in the general formula (I);
• (3) treating the product of step (2) with magnesium methyl carbonate to form the corresponding .alpha.-carboxy-.gamma.-spirolactone;
• (4) reacting an aliphatic amine with the .alpha.-carboxy-.gamma.-spirolactone of step (3) in the presence of formaldehyde or paraformaldehyde in a Mannich reaction;
• (5) reductively opening, if necessary, the lactone ring using lithium aluminum hydride;
• and
• (6) cyclizing by internal dehydration.