A SIMPLE ROUTE TO 1,2,3,4-TETRAMETHYLFULVENE AND TO 1-FUNCTIONALIZED 2,3,4,5-TETRAMETHYLCYCLOPENTADIENES

Jutzi P, Heidemann T, Neumann B, Stammler H-G. Ein einfacher Weg zu 1,2,3,4-Tetramethylfulven und zu 1-funktionalisierten 2,3,4,5-Tetramethylcyclopentadienen. Synthesis. 1992;1992(11):1096-1098.5-Bromo-1,2,3,4,5-pentamethylcyclopenta-1,3-diene, which is available in good yield from 1,2,3,4,5-pentamethylcyclopenta-1,3-diene, reacts with potassium tert-butoxide in the presence of catalytic amounts of 18-crown-6 under dehydrobromination to give 1,2,3,4-tetramethylfulvene (1,2,3,4-methyl-5-methylenecyclopenta-1, 3-diene, 1) in high yield. Compound 1 can be used to prepare various 1-functionalized 2,3,4,5-tetramethylcyclopentadiene systems. For example, reaction of lithium dimethylamide, allylmagnesium chloride, potassium indenide or 1,3-dithian-2-yllithium with 1 leads, after hydrolysis, to the corresponding substituted cyclopentadiene systems 3-6 in high yield