1,142,331. 2-Substituted cyclopentane-1,3- diones and 2-alkoxy alkylidene-cyclopent-4-ene- 1,3-diones. TAKEDA CHEMICAL INDUSTRIES Ltd. 17 Feb., 1966 [18 Feb., 1965], No. 7059/66. Heading C2C. The invention relates to a process for producing a 2-alkyl-cyclopentane- 1 ,3-dione compound of the formula wherein R is hydrogen or an alkyl group containing from one to three carbon atoms, in which a compound of the general formula is reduced by hydrogen in the prseence of a catalyst, e.g. palladium, nickel, ruthenium or platinum. The compound of Formula III may be prepared by reacting cyclopent-4-ene- 1,3-dione with an alkyl ester of an ortho acid of the formula wherein R<SP>1</SP> is an alkyl group containing one to four carbon atoms and R is as above. The invention also relates to compounds of Formula III. In an example ethyl ortho-formate and cyclopent-4-one-1,3-dione are reacted to produce 2-ethoxy-methylidene-cyclopent-4-ene- 1,3- dione which is separated and then treated with hydrogen gas in the presence of palladium carbon to yield 2-methyl-cyclopentane- 1,3-dione.