Stable carbonium ions. Part VII. Cycloaddition reactions of ferrocenylalkylium ions with cyclopentadiene

Abstract

The reaction of ferrocenylalkylium ions with cyclopentadiene proceeds stereoselectively to give 1 : 1 cycloaddition products which incorporate a bicyclo[3.2.1]oct-6-ene skeleton fused to a cyclopentadienyl ring (giving a methanoazulenyl structure). Both stereoisomeric forms of (π-cyclopentadienyl)[η- 1–3a(8a)-4,7-methano-7,8-dihydro-4H-azulenyl]iron(II) have been synthesised from cis-3-ferrocenylcyclopentanecarboxylic acid. The stereochemical features of the cycloaddition reactions have been established from the ¹H n.m.r. spectral properties of the products and their derivatives.