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Contents Vol 63(7)

New Thermal Routes to ortho-Benzyne

Katharine J. Cahill A , Aida Ajaz A and Richard P. Johnson A B
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A Department of Chemistry, University of New Hampshire, Durham, NH 03857, USA.

B Corresponding author. Email: rpj@cisunix.unh.edu

Australian Journal of Chemistry 63(7) 1007-1012 https://doi.org/10.1071/CH10074
Submitted: 10 February 2010  Accepted: 23 March 2010   Published: 15 July 2010

Abstract

There is experimental evidence that intermediate ortho-benzynes can be made by intramolecular [2 + 4] cycloaddition of a 1,3-diyne with an alkyne. Computations by several groups support a concerted mechanism for the cycloaddition of butadiyne with acetylene. High temperature benzyne cycloreversion has also been demonstrated experimentally; this may in fact be a common reaction in hydrocarbon fuel combustion. Following leads from earlier pyrolysis experiments, herein we predict that cycloaddition of benzyne with butadiyne can proceed by a stepwise mechanism to 2,3-naphthyne. However, a slightly lower energy path leads to a benzocyclobutadiene. ortho-Benzyne can be generated by solution-phase and solid-phase reaction in a microwave reactor. We have developed the method of microwave flash pyrolysis (MFP) for high temperature solid-phase microwave reactions. MFP reaction of phthalic anhydride, a classic benzyne precursor, results in a typical suite of products expected from a relatively high concentration of benzyne.


Acknowledgements

I am grateful to Professor Curt Wentrup for the invitation to write this account, and for generous support from the National Science Foundation (CHE-0910826). The senior author’s first association with benzyne came almost exactly 40 years ago as a sophomore organic chemistry student at Syracuse University. In a research project with Professor Roger Hahn, the very first reaction carried out was the preparation of benzonorbornadiene by reaction of benzyne with cyclopentadiene.[ 79 ] We later carried this on to a more general synthesis of benzo-fused bicyclic structures.[ 80 ] It is a great pleasure to make a small contribution to benzyne chemistry.


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