Differences in Stability Among Cyclic Boronic Esters

3 Differences in Stability Among Cyclic Boronic Esters 

Data allowing the comparison of common cyclic boronic esters, in terms of stability and reactivity, are scarce. 

0-B bond is linked to the most substituted C(4) atom in the ring. This confirms that the a methyl groups participate in B-0 bond stabilization. 

Many reactions of these boronic esters will involve in the first step a nucleophilic addition onto the boron atom, leading to a tetrahedral boronate anion. With a borolane, this would involve a decrease of the ring strain, and would be kineti-cally more favorable than with the corresponding borinane. Nevertheless, steric hindrance by the a methyl substituents will also be important. This is consistent with the work of Bowie and Musgrave, who compared the rates of hydrolysis of phenylboronic esters exposed to a water-saturated atmosphere, and found that unsubstituted phenylborolane was hydrolyzed faster than unsubstituted phenylborinane. Under the same conditions, phenylboronic esters of pinacol, neopentylglycol and hexyleneglycol were unaffected for several days. 

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