Cyclobutanone is an organic compound with molecular formula (CH2)3CO. It is a four-membered cyclic ketone (cycloalkanone). It is a colorless volatile liquid at room temperature. Since cyclopropanone is highly sensitive, cyclobutanone is the smallest easily handled cyclic ketone.
The Russian chemist Nikolai Kischner first prepared cyclobutanone in a low yield from cyclobutanecarboxylic acid.[1][2] Kischner's process, involving several steps, is cumbersome and inefficient; more efficient, high-yielding syntheses have since been developed.[3]
One strategy involves degradation of five-carbon building blocks. For example, the oxidative decarboxylation of cyclobutanecarboxylic acid was improved by the use of other reagents and methods.
A newer, more efficient preparation of cyclobutanone was found by P. Lipp and R. Köster in which a solution of diazomethane in diethyl ether is reacted with ketene.[4] This reaction is based on a ring expansion of the cyclopropanone intermediate initially formed, wherein molecular nitrogen is split off:
The reaction mechanism was confirmed by a reaction using 14C-labeled diazomethane.[5]
Another synthesis of cyclobutanone involves lithium-catalyzed rearrangement of oxaspiropentane, which is formed by epoxidation of the easily accessible methylenecyclopropane:[6][7]
At about 350 °C, cyclobutanone decomposes into ethylene and ketene.[9] The activation energy for this [2+2] cycloelimination is 52 kcal/mol. The reverse reaction, the [2+2] cycloaddition of ketene and ethylene, has never been observed.
