Cyclopropanone

Preparation

Cyclopropanone has been prepared by reaction of ketene with diazomethane in an unreactive solvent such as dichloromethane. These solutions are stable at −78 °C. In the presence of protic reagents such as carboxylic acids, primary and secondary amines, and alcohols, cyclopropanone converts to adducts, which are often isolatable at room temperature: :(CH2)2CO + X-H → (CH2)2C(X)(OH) (X-H = R2N-H, HO-H, RO-H)

Structure

The C3O atoms are coplanar. As deduced from the microwave spectrum, the H2C-CH2 bond length of 157.5 pm is unusually long. By contrast, the C-C bond lengths in cyclopropane are 151 pm. The C=O bond length of 119 pm is short compared to the 123 pm bond length in acetone.

The value of νC=O in the infrared spectrum is near 1815 cm−1, ca. 70 cm−1 higher than values for a typical ketone.

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 (formed by cleavage of the C2-C3 bond) is suggested as the active intermediate or even a biradical structure (compare to the related trimethylenemethane).

:[[Image:Cyclopropanonetautomericstructures.png|400px|Cyclopropanone tautomeric structures]]

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:

:[[Image:CyclopropanoneChemistry.png|400px|2,3-Dimethyl-2,3-diphenylcyclopropanone intermediate in photolysis]]

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 (with UV trace similar to isotoluene) followed by rearomatization. The energy difference between A and B is 5 to 7 kcal/mol (21 to 29 kJ/mol).

Coprine

The cyclopropanone derivative 1-aminocyclopropanol occurs naturally by hydrolyzes of coprine, a toxin in some mushrooms. 1-Aminocyclopropanol is an inhibitor of the enzyme acetaldehyde dehydrogenase.

References

References

1. (1987). "PATAI'S Chemistry of Functional Groups: Cyclopropyl Group".
2. (1969). "Cyclopropanones". Accounts of Chemical Research.
3. De Kimpe, Norbert. (2001). "Cyclopropanone".
4. (1985). "Cyclopropanone Ethyl Hemiacetal from Ethyl 3-Chloropropanoate". Organic Syntheses.
5. (1983). "Cyclopropanone Hemiacetals". Chemical Reviews.
6. (1970). "Thermal reactions of a cyclopropanone. Racemization and decarbonylation of trans-2,3-di-tert-butylcyclopropanone". Journal of the American Chemical Society.
7. (2007). "First Direct Detection of 2,3-Dimethyl-2,3-diphenylcyclopropanone". The Journal of Organic Chemistry.
8. (May 2002). "Mechanism of inhibition of aldehyde dehydrogenase by cyclopropanone hydrate and the mushroom toxin coprine". Biochemistry.