Nonafulvalen: Synthese durch oxidative Kupplung von Cyclononatetraenid und Valenzisomerisierung

Nonafulvalene: Synthesis by Oxidative Coupling of Cyclononatetraenide and Valence Isomerisation Following a general strategy ( Scheme 2 ) for the synthesis of fulvalenes by oxidative coupling of Hückel anions, the synthesis of nonafulvalene ( 1 ), has been realised ( Scheme 3 ). The most tricky step is a twofold deprotonation of bi(cyclononatetraenydl) 3 with K ( t ‐BuO) to give 4 ; it is only possible after equilibration 3⇄3a ; otherwise, deprotonation of one cyclononatetraene unit of 3 followed by oxidative coupling with AgBF 4 gives quater(cyclononatetraenyl) 12 as an isomeric mixture. The reaction of 3 with K gives potassium cct ‐cyclononatetraenide 11 ( M = K; Scheme 5 ) and not the dianion 4 as reported in the literature. Nonafulvalene ( 1 )is extremely reactive due to its very easy valence isomerisation to geve an isomeric mixture of tetrahydro‐dibenzopentafulvalenes 13 ( Scheme 4 ). The structure of crystalline isomer ( E‐anti )‐ 13 has been proved by X‐ray analysis.