The reaction of 7-chloronorbornadiene with n-butyllithium a novel rearrangement of norbornadienyl anion

✍ Scribed by Shun-Ichi Murahashi; Ken-ichi Hino; Yusuke Maeda; Ichiro Moritani

• Publisher: Elsevier Science
• Year: 1973
• Tongue: French
• Weight: 200 KB
• Volume: 14
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(01)96304-x

✦ Synopsis

Norbornadienylidene is of interest since extended calculation predicted that norbornadienylidene would have the difinitive probability of a singlet state stabilized nonclassical methylene (1). A possible &-elimination of 7-chloronorbornadiene g (2) to overcome the antiaromatic destabilization (3) of 7-norbornadienyl anion was examined. We now report that addition of n-butyllithium to the double bond ofAfavors over metalation at the 7-position of Agiving 6-chloronorbornenyl anion (3 which undergoes subsequent new rearrangement resulting in 1,3-elimination. Recently, the structure of norbornenyl anion was focussed on in connection to a symmetrical nonclassical anion and a classical 3-nortricyclic anion (4). Reaction of the chlorideLwith one-equivalent of n-BuLi in n-hexane at 0 produced CllH16 hydrocarbons in 60 % yield. Vpc analysis indicated the presence of two components in a5: 1 ratio. The minor product was assigned as 7-n-butylnorbornadiene (2 by comparison with the authentic sample derived from 7-t-butoxynorbornadiene and n-BuMgBr. The main highly unstable olefin (3 was purified by short-path distillation (go"/2 mn Hg). The nmr spectrum exhibited five vinyl protons at 6.50-5.50 (m), two ally1 protons at 2.93 (s), two ally1 protons at 2.08 (m), four methylene protons at 1.7-1.1 (m), and three methyl protons at 0.89. Double irradiation experiment indicated trans-configuration ofA(JHaHb = 15 Hz). This seems to be consistent with that expected to 2-(1-trans-n-hexenyl)cyclopentadiene w. Confirmation of this structural assignment was achieved either by hydrogenation over Pd/C leading to l-nhexylcyclopentene or by treatment with TCNE leading to the cycle-adduct, which showed satisfactry elemental analysis, mp 127-128', m/e 276, nmr66.4-6.25 (H, m), 6.05-5.78 (2H, m),