Bicyclobutane is an organic compound with the formula C4H6. It is a bicyclic molecule consisting of two cis-fused cyclopropane rings, and is a colorless and easily condensed gas. Bicyclobutane is noted for being one of the most strained compounds that is isolatable on a large scale — its strain energy is estimated at 63.9 kcal mol−1. It is a nonplanar molecule, with a dihedral angle between the two cyclopropane rings of 123°.
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||54.092 g·mol−1|
|Boiling point||8.3 ± 0.2 °C|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
The first reported bicyclobutane was the carboxyethyl derivative, C4H5CO2Et, which was prepared by dehydrohalogenation the corresponding bromocyclobutanecarboxylate ester with sodium hydride. The parent hydrocarbon was prepared from 1-bromo-3-chlorocyclobutane by conversion of the bromocyclobutanecarboxylate ester, followed by intramolecular Wurtz coupling using molten sodium. The intermediate 1-bromo-3-chlorocyclobutane can also be prepared via a modified Hunsdiecker reaction from 3-chlorocyclobutanecarboxylic acid using mercuric oxide and bromine:
Stereochemical evidence indicates that bicyclobutane undergoes thermolysis to form 1,3-butadiene with an activation energy of 41 kcal mol−1 via a concerted pericyclic mechanism (cycloreversion, [σ2s+σ2a]).
Multiple research groups have reported success in synthesizing bicyclobutane-containing molecules using enzymes in living cells. One group reported the transformation of linolenic acid into a bicyclobutane fatty acid via a protein produced by a strain of the cyanobacterium Anabaena sp. (strain PCC 7120). The other group reported a directed evolution approach, whereby engineered heme protein was expressed in E. coli and successfully optimized for increased rate and yield of biosynthesis of a substituted bicyclobutane derivative.
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