Fulvene having substituents only on 1-, 4-, and 6-positions: a key intermediate for novel ansa-metallocene complexes

A synthetic route for 1,4-dimethyl-6-phenylfulvene (4) and 1,4-dimethyl-6,6-diphenylfulvene (5), which are characteristic in that they have substituents only on 1-, 4-, and 6-positions, is developed. The synthetic route is straightforward from 2-bromo-3-methyl-2-cyclopenten-1-one ethylene ketal (1), which can be easily synthesized in 100-g scale. Overall yield from 1 is 50 and 47% for 4 and 5, respectively. Synthesis of an ansa-metallocene complex, [Ph(H)C(fluorenyl)(1,3-Me2Cp)]ZrCl2 (7), is demonstrated using 4. Much higher comonomer incorporation in ethylene/1-hexene copolymerization and dramatic increase of molecular weight in 1-hexene polymerization are observed with 7 when the reactivity compared with that of the one not having methyl substituents, [Ph(H)C(fluorenyl)(Cp)]ZrCl2.