Competing pathways in the [2+2] cycloadditions of cyclopentyne and benzyne. A DFT and ab initio study

Ozkan I., Kinal A.

JOURNAL OF ORGANIC CHEMISTRY, vol.69, no.16, pp.5390-5394, 2004 (Peer-Reviewed Journal) identifier identifier identifier

  • Publication Type: Article / Article
  • Volume: 69 Issue: 16
  • Publication Date: 2004
  • Doi Number: 10.1021/jo049542f
  • Journal Indexes: Science Citation Index Expanded, Scopus
  • Page Numbers: pp.5390-5394


The [2 + 2] cycloadditions of cyclopentyne and benzyne to ethylene are explored at the B3LYP and CASSCF levels, supplemented by CCSD(T) and CAS-MP2 calculations at the stationary points. The biradical path in the benzyne system is computed to be about 4.1 kcal/mol lower than the concerted path, consistent with the experimentally observed loss of original stereochemistry in this cycloaddition. However, computations fail to confirm the 99% stereoretention in the corresponding reaction of cyclopentyne. The concerted and biradical paths in the latter reaction are found to involve nearly isoenergetic barriers, thus predicting only about 75% stereoretention. More sophisticated theoretical methods seem to be needed to resolve the issue in the cyclopentyne system.