Oxidative Coupling of 2-Alkyl-6,6-dimethylpentafulvenyl Anions

Article abstract of DOI:10.1002/hlca.19930760411

CuCl2-Induced oxidative coupling of 2-(tert-butyl)-6,6-dimethylpentafulvenyl anion 9 predominantly takes place at C(7) and C(5) to give <7-7> and <7-5> coupling products 15 and 16 in 35 and 47percent yields, respectively (Scheme 3) whose structures are elucidated from 1D- and 2D-NMR analysis.Compared with the product distribution observed for 6,6-dimethylpentafulvenyl anion 2 (Scheme 1), no coupling at C(2)/C(3) of 9 is observed.This means that, besides electronic effects, steric effects are also important in oxidative coupling of fulvenyl anions.The same couplings occur in the case of 2,3-bis(6,6-dimethylfulven-2-yl)-2,3-dimethylbutane dianion 10 as well, but, due to electronic as well as conformational effects (Scheme 5), intermolecular coupling (to give polymers 17, Scheme 4) is strongly favored over intramolecular coupling.Mechanisms explaining base-catalyzed isomerization 15a <-> 15b <-> 15c (Scheme 6) as well as isomerization 16a <-> 16b (Scheme 7) are proposed.