Many boronic acids, including 2-heterocyclic, vinyl, and cyclopropyl derivatives, are inherently unstable, which can limit their bench-top storage and/or efficient cross-coupling. The authors herein report the 1st general soln. to this problem: in situ slow release of unstable boronic acids from the corresponding air-stable N-methyliminodiacetic acid (MIDA) boronates. N-Boc-pyrrole-2-boronic acid MIDA ester is an example.