Cyclopropanone


Cyclopropanone is an organic compound with molecular formula 2CO consisting of a cyclopropane carbon framework with a ketone functional group. The parent compound is labile, being highly sensitive toward even weak nucleophiles. Surrogates of cyclopropanone include the acetals.

Preparation

Cyclopropanone has been prepared by reaction of ketene with diazomethane at −145 °C. Derivatives of cyclopropanone are of some interest to organic chemistry.

Derivatives

Cyclopropanones are intermediates in the Favorskii rearrangement with cyclic ketones where carboxylic acid formation is accompanied by ring-contraction.
Cyclopropanones react as 1,3-dipoles in cycloadditions for instance with cyclic dienes such as furan. An oxyallyl intermediate or valence tautomer is suggested as the active intermediate or even a biradical structure.
Experimental evidence is not conclusive. Other reactions of cyclopropanones take place through this intermediate. For instance enantiopure -trans-2,3-di-tert-butylcyclopropanone racemizes when heated to 80 °C.
An oxyallyl intermediate is also proposed in the photochemical conversion of a 3,5-dihydro-4H-pyrazole-4-one with expulsion of nitrogen to an indane:
In this reaction oxyallyl intermediate A, in chemical equilibrium with cyclopropanone B attacks the phenyl ring through its carbocation forming a transient 1,3-cyclohexadiene C followed by rearomatization. The energy difference between A and B is 5 to 7 kcal/mol.