Cyclobutanone
Cyclobutanone is an organic compound with molecular formula 3CO. It is a four-membered cyclic ketone. It is a colorless volatile liquid at room temperature. Since cyclopropanone is highly sensitive, cyclobutanone is the smallest easily handled cyclic ketone.
Preparation
The Russian chemist Nikolai Kischner first prepared cyclobutanone in a low yield from cyclobutanecarboxylic acid. Kischner's process, involving several steps, is cumbersome and inefficient; more efficient, high-yielding syntheses have since been developed.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. 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.
Another synthesis of cyclobutanone involves lithium iodide catalyzed rearrangement of oxaspiropentane, which is formed by epoxidation of the easily accessible methylenecyclopropane:
Cyclobutanone can also be prepared in a two step procedure by dialkylation of 1,3-dithiane with 1-bromo-3-chloropropane followed by deprotection to the ketone with mercuric chloride and cadmium carbonate.
Cyclobutanones are the intermediates of the homo-Favorskii rearrangement, and can be isolated when nucleophiles are absent, as in the synthesis of kelsoene: