Photocycloaddition of fumaronitrile to adamantan-2-ones and modification of face selectivity by inclusion in β-cyclodextrin and its derivatives

Abstract

The face selectivity in 5-substituted-adamantan-2-ones (1–Xs) can be dramatically reversed by means of inclusion into β-Cyclodextrin (β-CD) and its heptakis(6-O-hydroxypropyl), heptakis(6-O-acetyl), heptakis(2,3,6-tri-O-methyl) and heptakis(2,3,6-tri-O-acetyl) derivatives. The 5-substituents varied from fluoro, chloro, bromo, phenyl to trimethylsilyl, and face selectivities of the oxetane formation have been found to vary with the sizes of 5-substituents and cavities of β-CDs. A 98:2 face selectivity was achieved when 1-SiMe₃ was used as a probe. The effect observed is interpreted by assuming that the carbonyl π-face syn to the bulky 5-substituent is partially blocked by the torus of the host due to complexation of 1-X and CD. Information obtained from ¹H NMR titration and X-ray powder diffraction study on the inclusion complex is consistent with the above explanation. X-Ray single-crystal structure was used to determine the oxetane structure of anti-2-SiMe₃.