Cyclobutanes and Cyclobutenes from Photochemical Cleavage of Some Bicyclo[3.2.0]heptan-2-ones

Leiv K. Sydnes; Doan Van Ha

doi:10.1071/CH08391

RESEARCH ARTICLE

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Cyclobutanes and Cyclobutenes from Photochemical Cleavage of Some Bicyclo[3.2.0]heptan-2-ones

Leiv K. Sydnes ^A ^B and Doan Van Ha ^A

+ Author Affiliations

- Author Affiliations

^A Department of Chemistry, University of Bergen, Allégt. 41, NO-5007 Bergen, Norway.

^B Corresponding author. Email: leiv.sydnes@kj.uib.no

Australian Journal of Chemistry 62(2) 101-107 https://doi.org/10.1071/CH08391
Submitted: 16 September 2008 Accepted: 17 December 2008 Published: 19 February 2009

Abstract

Irradiation of solutions of cyclopent-2-enone or 3-methylcyclopent-2-enone and allyl alcohol with light from a medium-pressure mercury lamp through a Pyrex filter with a cut-off at 295 nm furnishes excellent yields of isomeric mixtures of substituted bicyclo[3.2.0]heptan-2-ones as the primary products. Both enones give predominantly the head-to-head isomer with exo stereochemistry. The primary products turn out to be photolabile and undergo Norrish type I cleavage followed by hydrogen abstraction, but the outcome is influenced by the presence of a methyl group at C5. In the absence of such a methyl group the C1–C2 bond is cleaved, to give rise to two cyclobutenyl aldehydes in better than 90% combined yield; when a methyl group is attached at C5 both C–C bonds to the carbonyl group are broken and a mixture of cyclobutyl aldehydes and ketenes are formed in close to quantitative combined yield.

Acknowledgements

Financial support from Norsk Hydro to purchase chemicals is very much appreciated. The School of Chemistry, University of New South Wales, Sydney, Australia, and School of Chemical & Physical Sciences, Victoria University of Wellington, New Zealand, are gratefully acknowledged for providing excellent working conditions during a recent sabbatical stay. Valuable discussions with Professor Brian Halton at the latter institution are highly appreciated, and so is valuable feedback from one of the referees.

References

Cyclobutanes and Cyclobutenes from Photochemical Cleavage of Some Bicyclo[3.2.0]heptan-2-ones

Abstract

Acknowledgements

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