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

✍ Scribed by Shaochun You; Markus Neuenschwander

• Publisher: John Wiley and Sons
• Year: 1993
• Tongue: German
• Weight: 789 KB
• Volume: 76
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19930760411

✦ Synopsis

CuC1,-Induced oxidative coupling of 2-(rertbutyl)-6,6-dimethylpentafulvenyl anion 9 predominantly takes place at C(7) and C(5) to give [7-71 and (7-51 coupling products 15 and 16 in 35 and 47% yields, respectively (Scheme 3 ) whose structures are elucidated from IDand 2D-NMR analysis. Compared with the product distribution observed for 6,6-dimethylpentafulvenyl anion 2 (Scheme I ) , no coupling at C(2)/C(3) of 9 is observed. This means that, besides electronic effects, steric effects are also important in oxidative couplings 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 e 1% (Scheme 6 ) as well as isomerization 16a e 16b (Scheme 7 ) are proposed. ') *) ') 4, Coupling Reactions, Part 11; Part 10: [I]. Part of the dissertation [2].

Compounds 6 and 7 are obtained as mixtures of tautomeric cyclopentadienes, while crystalline tautomer 8 has been isolated. The mechanism of the Cu"-induced coupling reaction of 2 is still unknown. So it is not yet clear whether dimerization proceeds by recombination of free fulvenyl radicals 3 or by C-C bond formation out of a metalorganic complex of 2.