Young Chul Won, U. Joung, Eun Sook Cho
May 6, 2004
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Journal
Synthesis
Abstract
2-Bromo-3-methoxy-1,3-dimethylcyclopentene (3) is synthesised in 85% yield in 80 g scale by 1,2-addition of MeLi to 2-bromo-3-methyl-2-cyclopenten-1-one and subsequent in situ treatment of Mel. Addition of n-BuLi to the bromo-compound 3 in Et 2 O affords 2-lithio-3-methoxy-1,3-dimethylcyclopentene (1). Successive addition of RCHO [R = CH 3 , (CH 2 ) 2 CH 3 , CH(CH 3 ) 2 , C(CH 3 ) 3 , H] and Mel to the lithium compound and aqueous acidic work-up provide cyclopentadiene compounds, 2-[CHR(OMe)]-1,3-Me 2 C 5 H 3 in 60-84% yields. Treatment of the cyclopentadienes with NaH or KH in pentane affords 1,4,6-trimethylfulvene, 6-n-propyl-1,4-dimethylfulvene, 6-isopropyl-1,4-dimethylfulvene, 6-tert-butyl-1,4-dimethylfulvene and 1,4-dimethylfulvene in 67-83% yields. Ligand for an ansa-metallocene complex, CH 2 C(1,3-Me 2 Cp) 2 ZrCl 2 , can be shortly afforded in 64% yield by reacting the lithium compound 1 with the newly synthesized 1,4-dimethylfulvene.