1,3-Cyclobutanedione is an organic compound with the formula (CH2)2(CO)2. It is an isomer of 1,2-cyclobutanedione. The compound would be of little interest except that its tautomer is a subunit in some commercial dyes.

In solution, 1,3-cyclobutanedione exists in equilibrium with a less stable tautomer, called squaraine, 3-hydroxycyclobut-2-enone. Squaraine dyes are, formally at least, derivatives of squaraine. In such dyes, the ene-one tautomer predominates.

1,3-cyclobutanedione and its enol tautomer.

The mixture of tautomers can be prepared by hydrolysis of 1-ethoxycyclobutene-3-one, which is prepared from the cycloaddition of ethoxyacetylene to ketene.

Substituted derivatives

A variety of substituted 1,3-Cyclobutanediones form upon spontaneous dimerization of disubstituted ketenes. 2,2,4,4-Tetramethylcyclobutanedione is thus formed by dehydrochlorination of isobutyryl chloride:

(CH3)2CHCOCl + Et3N → (CH3)2C=C=O + Et3NHCl

2 (CH3)2C=C=O → (CH3)2C)2(C=O)2

Ketene itself dimerizes mainly to give the lactone called diketene as well as a small amount of 1,3-cyclobutanedione.

Related compounds

  • Moniliformin, a naturally occurring derivative of 3-hydroxycyclobut-2-enone