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Paper | Regular issue | Vol 60, No. 12, 2003, pp.2743-2748
Published online, 14th October, 2003
DOI: 10.3987/COM-03-9908
New Chiral Synthesis of Methyl and Allyl Disubstituted Butyro Lactone: A Formal Synthesis of (-)-Ngaione

Katsufumi Suzuki, Kohei Inomata,* and Yasuyuki Endo

*Tohoku Pharmaceutical University, 4-4-1 Komatsushima, Aoba-ku, Sendai 981-8558, Japan

Abstract

A new chiral synthesis of butyrolactone [(-)-7] bearing methyl and allyl substituents at the γ-position has been established via diastereoselective continuous nucleophilic addition to the chiral tricyclic lactone [(-)-1] as the key step. In practice, continuous nucleophilic addition to the tricyclic lactone [(-)-1] by using the combination of methyllithium and allylmagnesium bromide proceeded to yield the corresponding diol (8) diastereoselectively. After oxidation of 8, enantiopure methyl and allyl disubstituted butenolide (10) was obtained via retro-Diels-Alder reaction. Selective 1,4-reduction of 10 afforded the corresponding butyrolactone [(-)-7], which is the key intermediate for (-)-ngaione synthesis.