Novel formation of iodobenzene derivatives from 1-(methylthio)-3-tosylhexa-1,3-dien-5-ynes via iodine-induced intramolecular cyclization.
The reaction of (1E,3E)-1-(methylthio)-3-tosylhexa-1,3-dien-5-ynes (3) with iodine to form iodine-substituted benzenes (4) is reported. The reaction of 3 with iodine proceeded very slowly, but UV irradiation accelerates the reaction to give 4 in high-to-excellent yields. Irradiation induces the cis-trans isomerization of the C1-C2 double bond, leading to the (1Z,3E)-geometric isomer (3'), which easily reacts with iodine to afford 4. This reaction is applicable to 3-(methoxycarbonyl)-1-(methylthio)-6-phenylhexa-1,3-dien-5-yne (11), which is synthesized as a geometric mixture. Interestingly, this mixture can be used as the starting material. Irradiation of the mixture (the geometric isomer ratio = 50:28:5:17) with iodine resulted in the formation of methyl 3-iodo-4-phenylbenzoate (12) in 80% yield.
Matsumoto
Shoji
S
Department of Applied Chemistry and Biotechnology, Graduate School of Engineering, Chiba University, 1-33 Yayoicho, Inageku, Chiba 263-8522, Japan.
Takase
Kenji
K
Ogura
Katsuyuki
K