Novel enhancement of diastereoselectivity of [2 + 2] photocycloaddition of chiral cyclohexenones to ethylene by adding naphthalenes.
The additive effect on the diastereoselective [2 + 2] photocycloaddition of chiral cyclohexenones 1 to ethylene is examined. A novel and fairly efficient method of increasing the diastereoselectivity in the reaction of 1a was elucidated. The de value increased from 56% to 83% by the addition of 1-phenylnaphthalene. The major product 2a was isolated by the recrystallization of the diastereomeric mixture (major/minor = 11/1), of which X-ray analysis confirmed the absolute configuration of the bicyclic system of 2a. Hydrolysis for removing the chiral auxiliary and subsequent esterification afforded the optically pure bicyclo[4.2.0]octanone derivative 5. From the fluorescence spectral analyses and other experimental results, the additive effect is attributed to the complex formation of chiral cyclohexenone 1a and added naphthalenes.
Tsutsumi
Ken
K
Graduate School of Materials Science, Nara Institute of Science and Technology (NAIST), 8916-5 Takayama, Ikoma, Nara 630-0192, Japan. tsutsumi@ms.aist-nara.ac.jp
Nakano
Hiroaki
H
Furutani
Akinori
A
Endou
Katsunori
K
Merpuge
Abdurshit
A
Shintani
Takuya
T
Morimoto
Tsumoru
T
Kakiuchi
Kiyomi
K