Diastereodifferentiating the [2+2] photocycloaddition of ethylene to arylmenthyl cyclohexenonecarboxylates: stacking-driven enhancement of the product diastereoselectivity that is correlated with the reactant ellipticity.
Upon diastereodifferentiating the [2+2] photocycloaddition of ethylene to a series of p-substituted (-)-8-phenylmenthyl cyclohexenonecarboxylates, the diastereoselectivity was critically controlled by the nature of the substituent introduced to the chiral auxiliary, and the p-nitro-substituted substrate afforded the cycloadducts in 90% diastereomeric excess (de) and with 97% isolated yield. Detailed experimental and theoretical conformation analyses revealed that the stacking interaction of the aromatic auxiliary with the cyclohexenone moiety plays the decisive role in determining the substrate conformation and is, therefore, responsible for the dramatic enhancement of the de. Of particular interest, the product de was directly related to the ellipticity of the substrate, enabling us to "predict" the de prior to photoirradiation.
Tsutsumi
Ken
K
Graduate School of Materials Science, Nara Institute of Science and Technology (NAIST), Takayama, Ikoma, Nara 630-0101, Japan.
Yanagisawa
Yuuki
Y
Furutani
Akinori
A
Morimoto
Tsumoru
T
Kakiuchi
Kiyomi
K
Wada
Takehiko
T
Mori
Tadashi
T
Inoue
Yoshihisa
Y