Synthesis of 4-(6-Fulvenyl)[2.2]paracyclophane and Its Derivatives

Abstract

Thiele condensation of the [2.2]paracyclophane derivatives 8, 12, 22, and 23 with cyclopentadiene (9) led to the monofulvenes 10, 11, and 13 and the bis(fulvenes) 24 and 25. Likewise, condensations of 8 with 1,2,3,4-tetrachlorocyclopentadiene (14) and 1,2,3,4-tetraphenylcyclopentadiene (16) provided the 4-fulvenyl[2.2]paracyclophanes 15 and 17. For comparison purposes, 8 was also condensed with lithium fluorenide (18) and lithium indenide (20) to give the benzo-annelated derivatives 19 and 21, respectively. Reactions of the dialdehydes 22 and 23 led to the bis(indenes) 26 and 27. 4-(6-Fulvenyl)[2.2]paracyclophane exists as two conformational isomers, 10 (major product) and 11 (minor product). By temperature-dependent NMR spectroscopy, the rotational barrier associated with 11 ⇄ 10 interconversion has been determined as ca. 26 kcal mol−1 at 70 °C. The structures of 19 and 27 have been established by single-crystal X-ray crystallography.