title: Chemistry of Zerumbone. 1. Simplified Isolation, Conjugate Addition Reactions, and a Unique Ring Contracting Transannular Reaction of Its Dibromide.
abstract: Zerumbone (1) was isolated from fresh rhizomes of Zingiber zerumbet Smith in yields of 0.3-0.4% by simple steam distillation and recrystallization. 1 accepted 2 equiv of hydrogen cyanide at the C6 and C9 double bonds of the cross-conjugated dienone system to give a mixture of diastereomers 3a-d. In the presence of potassium cyanide, the dominant isomer 3a was isomerized to a mixture of 3a-d. Under controlled conditions, 1 added one mole of methanol regio- and stereoselectively at the C6 double bond to give adduct 4a. With potassium cyanide, 4a was transformed to the mixture of 3a-d. 1 took up one mole of bromine at C6 double bond to give a diastereomeric mixture of adducts 5a and 5b. Treatment of 5a with potassium cyanide gave a mixture of cyclopropanecarboxylic acid 6a and 6b. This unique ring-contracting cyclopropane formation is pictured as a sequential Favorskii type reaction. alpha-Cyclodextrin improved the selectivity and yields of the reactions conducted in an aqueous medium.
authors.affiliation: Kyoto University of Education, Fushimi, Kyoto 612-0863, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Kitayama
authors.forename: Tadashi
authors.initials: T
authors.lastname: Okamoto
authors.forename: Richard K.
authors.initials: RK
authors.lastname: Hill
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Kawai
authors.forename: Sho
authors.initials: S
authors.lastname: Takahashi
authors.forename: Shigetomo
authors.initials: S
authors.lastname: Yonemori
authors.forename: Yukio
authors.initials: Y
authors.lastname: Yamamoto
authors.forename: Kouichi
authors.initials: K
authors.lastname: Ohe
authors.forename: Sakae
authors.initials: S
authors.lastname: Uemura
authors.forename: Seiji
authors.initials: S
authors.lastname: Sawada