Site-selective C-H functionalization in a cyclodextrin metal-organic framework

Confinement is a unifying element in selective enzymatic reactions but has rarely been used to control site selectivity of carbon- hydrogen (C-H) bond functionalization in artificial receptors. Herein, we demonstrate the selective functionalization of one of seven C(sp3)-H bonds on a D-glucopyranosyl residue of y-cyclodextrin (y -CD) by irradiating 2-benzoylbenzoate in a y-cyclodextrin-contain- ing metal -organic framework (CD-MOF-1). Both 1H NMR spectroscopy and X-ray crystallography of the products confirm that functionalization occurs selectively at one of the two C(sp3)-H bonds on the C6 position of a D-glucopyranosyl residue. The alignment of 2-benzoylbenzoate inside (y-CD)2 tunnels in CD-MOF-1, as revealed by X-ray crystallography, precludes C-H functionalization on the outer surface of the y -CD tori. Theoretical calculations indicate less steric hindrance associated with C6-functionalized (y-CD)2 tunnels in CD-MOF-1 compared with C3 and C5, leading to the observed site selectivity.