2-Lithio-3-methoxy-1,3-dimethylcyclopentene: A Synthetic Equivalent of 2-Lithio-1,3-dimethylcyclopentadiene and Useful Synthon for 6-Alkyl-1,4-dimethylfulvenes and ansa-Metallocene Complexes

Young Chul Won; Ui Gab Joung; Eun Sook Cho; Bun Yeoul Lee; Hyosun Lee; Young-Whan Park; Kwang Ho Song

doi:10.1055/s-2004-822324

PAPER

2-Lithio-3-methoxy-1,3-dimethylcyclopentene: A Synthetic Equivalent of 2-Lithio-1,3-dimethylcyclopentadiene and Useful Synthon for 6-Alkyl-1,4-dimethylfulvenes and ansa-Metallocene Complexes

Young Chul Won^a, Ui Gab Joung^a, Eun Sook Cho^a, Bun Yeoul Lee*^a, Hyosun Lee^b, Young-Whan Park^b, Kwang Ho Song^c
^a Department of Molecular Science and Technology, Ajou University, Suwon 442-749, Korea
Fax: +82(31)2192519; e-Mail: bunyeoul@ajou.ac.kr;
^b LG Chem Ltd., Research Park, 104-1, Munji-dong, Yuseong-gu, Daejon 305-380, Korea
^c Department of Chemical & Biological Engineering, Korea University, Seoul 136-701, Korea

Abstract

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Abstract

2-Bromo-3-methoxy-1,3-dimethylcyclopentene (3) is synthesized 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 MeI. Addition of n-BuLi to the bromo-compound 3 in Et₂O affords 2-lithio-3-methoxy-1,3-dimethylcyclopentene (1). Successive addition of RCHO [R = CH₃, (CH₂)₂CH₃, CH(CH₃)₂, C(CH₃)₃, H] and MeI to the lithium compound and aqueous acidic work-up provide cyclopentadiene compounds, 2-[CHR(OMe)]-1,3-Me₂C₅H₃ 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, CH₂C(1,3-Me₂Cp)₂ZrCl₂, can be shortly afforded in 64% yield by reacting the lithium compound 1 with the newly synthesized 1,4-dimethylfulvene.

Key words

fulvene synthesis - cyclopentadienes - metallocenes - lithiation - organometallic reagents

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References

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