Incorporation of an allene unit into alpha-pinene: Generation of the cyclic allene 2,7,7-trimethylbicyclo[4.1.]octa-2,3-diene and its dimerization

AZIZOGLU A., OZEN R., Hokelek T., BALCI M. N.

JOURNAL OF ORGANIC CHEMISTRY, vol.69, no.4, pp.1202-1206, 2004 (SCI-Expanded) identifier identifier identifier

  • Publication Type: Article / Article
  • Volume: 69 Issue: 4
  • Publication Date: 2004
  • Doi Number: 10.1021/jo035450z
  • Journal Name: JOURNAL OF ORGANIC CHEMISTRY
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.1202-1206
  • Hacettepe University Affiliated: Yes

Abstract

The reaction of etheral methyllithium with 3,3-dibromo-2,7,7-trimethyl-tricyclo[4.1.1.0.(2,4)] octane (2) was investigated. The generated carbene 12 undergoes intramolecular C-H insertion to provide the tetracyclic hydrocarbon 3 and the bicyclic allene 15, which undergoes [2 + 2] cyclodimerization. The structures of the formed allene dimers 16, 17, and 18 were elucidated by spectral means. The activation barriers for all possible C-H insertion products 3, 13, and 14 and the allene 15 were investigated by using density functional theory computations at the B3LYP/6-31G(d) level. It was found that the activation barriers for the formation of 3 and 15 (6.2 and 6.3 kcal mol(-1)) are much lower than that for the insertion products 13 and 14 (17.5 and 12.6 kcal mol(-1)), respectively. This prediction was completely in agreement with our experimental results.