Summary: 4932 J. Am. Chem. SOC.1986,108,4932-4937
Studies in the Cycloproparene Series: A Theoretical and
Experimental Study of the Cyclopropabenzynes'
Yitzhak Apeloig,*+Dorit Arad,+Brian Halton,**and Clifford J. Randallf
Contribution from the Department of Chemistry, Technion-Israel Institute of Technology,
Haifa 32000, Israel, and the Department of Chemistry, Victoria University of Wellington,
Private Bag, Wellington, New Zealand. Received February 3, 1986
Abstract: The highly strainedcyclopropabenzynes13and 15have been generatedby use of the complex base system of tert-butoxide
ion/amide ion, commencing with 2- and 3-bromocyclopropabenzene. Benzynes 13 and 15 have been trapped as the furan
adducts 14and 16,respectively. Fully optimized geometriesof 13and 15,their relative energies,and the strain and electronic
properties, as well as the regioselectivity of addition of 13,have been examined by ab initio molecular orbital calculations.
13 is predicted to be less stable than 15 by ca. 2.5 kcal-mol-' (based on a 3-21G* energy difference of 7.4 kcalsmol-' and on
an estimated correction of 5 kcal.mol-' for the difference in correlation energy). In 15 the strain of either the triple bond
or the cyclopropene ring is similar to that in benzyne and cyclopropabenzene, respectively.
The study of strained organic molecules has provided a wealth
of fascinating experimental chemistry and significant theoretical
challenge.2 Whilst the chemistry of the cycloproparenes, e.g.,
1, has been examined systematically3and the bonding and en-
ergetics of the parent molecule have been accounted for on a
theoretical basis,4 the limits to which such stress and strain can