New phenylboronic esters derived from inositol [1]

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Abstract
We have prepared two new tetracyclic phenylboronic esters 4 and 5 derived from myo‐inositol and from 1,2‐O‐isopropylidene‐myo‐inositol, respectively. The structures of these compounds were established from NMR and IR spectra, elemental analyses, and an X‐ray diffraction study in the case of 4. Compound 4 is a tetracyclic derivative of the less stable conformer of inositol (five axial hydroxy groups and one equatorial) with two dioxaboroline rings at opposite faces of the six‐membered ring, one formed between the boron atom and the axial hydroxyl groups at C‐3 and C‐5 and the other between the boron atom and the hydroxyl groups at C‐4 and C‐6, and a dioxaborolidine ring bridging C‐1 and C‐2 at axial and equatorial positions. A similar structure was found for 5 with the difference that bridging C‐1 and C‐2 there is a dioxolane ring. The boron atoms are planar with their attached atoms, stabilized by retrocoordination between the boron and oxygen and carbon atoms, respectively. The two phenyl rings that are in the same face of the molecule are essentially parallel, with a dihedral angle between planes of 28.26 ± 0.79°.