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

Claim 1

A process for the preparation of a 2-alkylcyclopenten-2-one having formula: where R is C n H 2n+1 (linear or branched); (CH 2 ) n --COOR'; (CH 2 ) n --NR' 2 ; (CH 2 ) n --OR'; (CH 2 ) n X or (CH 2 ) 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°-100° 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 + [CH(COOR") 2 ] - (R" being an ethyl, isopropyl or isobutyl radical), in the presence of the malonic ester COOR"--CH 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°-160° C., thereby obtaining a gamma-alkyl-lactone having formula (V).