Industrially advantageous processes for producing a 2-alkyl-2-cyclopentenone in high yields starting from a 2-(1-hydroxyalkyl)cyclopentanone or a 2-alkylidenecyclopentanone, which are obtainable from a cyclopentanone and a carbonyl compound. A 2-(1-hydroxyalkyl)cyclopentanone represented by the following general formula (1):
1
(wherein R
1
, R
2
, R
3
, R
4
, R
5
, R
6
and R
7
each independently represents hydrogen atom, an alkyl group having 1 to 10 carbon atoms which may have one or more substituents or an aromatic group which may have one or more substituents, and each of (1) R
6
or R
7
with R
3
and (2) R
6
or R
7
with R
4
or R
5
may be together combined to form a ring which may have a double bond) is subjected to dehydrative isomerization in the presence of a bromine compound and/or an iodine compound.
Industrially advantageous processes for producing a 2-alkyl-2-cyclopentenone in high yields starting from a 2-(1-hydroxyalkyl)cyclopentanone or a 2-alkylidenecyclopentanone, which are obtainable from a cyclopentanone and a carbonyl compound. A 2-(1-hydroxyalkyl)cyclopentanone represented by the following general formula (1):
is subjected to dehydrative isomerization or a 2- alkylidenecyclopentanone represented by the following general formula (3):
is isomerized. Both reactions take place in the presence of a bromine compound and/or an iodine compound.
In the above formulae, R1-R7 have the meanings given in the description.