Process for the preparation of 2-alkyl cyclopent-2-enones

A process for the preparation of a 2-alkylcyclopenten-2-one having formula:

• where R is C.sub.n H.sub.2n+1 (linear or branched);
• (CH.sub.2).sub.n --COOR';
• (CH.sub.2).sub.n --NR'.sub.2 ;
• (CH.sub.2).sub.n --OR';
• (CH.sub.2).sub.n X or (CH.sub.2).sub.n --CN, n ranges from 1 to 20, X is Cl, Br, I or F, and R' is an alkyl group containing up to 5 carbon atoms, a benzyl group, or a phenyl group, the last two groups having optionally one or more substituent groups on the ring, wherein a saturated gamma-alkyl-lactone:
• ##STR21## is reacted at 20.degree.-100.degree. C. with a protic acid, thereby obtaining, by rearrangement, a 2-alkyl-cyclopenten-2-one (I), characterized in that said gamma-alkyl-lactone (V) is obtained through the following steps:
• (a) an epoxide:
• ##STR22## is made to react with an alkylating agent having the formula Na.sup.+ [CH(COOR").sub.2 ].sup.- (R" being an ethyl, isopropyl or isobutyl radical), in the presence of the malonic ester COOR"--CH.sub.2 --COOR" and of an alcoholic solvent R"OH, the alkylating agent being in substantially equimolar ratio with respect to said epoxide and the malonic ester being in a molar ratio, with respect to said epoxide, of from 0.5 to 2, an alpha-carbalkoxy-gamma-alkyl-lactone being thus obtained having the formula:
• ##STR23## (b) said carbalkoxy-alkyl-lactone (IV) is saponified in an alkaline medium, thereby obtaining the corresponding acid, and such acid is decarboxylated, at 100.degree.-160.degree. C., thereby obtaining a gamma-alkyl-lactone having formula (V).