MIDA boronates are hydrolysed fast and slow by two different mechanisms

Jorge A. Gonzalez, O. Maduka Ogba, Gregory F. Morehouse, Nicholas Rosson, Kendall N. Houk, Andrew G. Leach, Paul H.-y. Cheong, Martin D. Burke, Guy C. Lloyd-jones

Research output: Contribution to journalArticlepeer-review

Abstract

MIDA boronates (N-methylimidodiacetic boronic acid esters) serve as an increasingly general platform for small-molecule construction based on building blocks, largely because of the dramatic and general rate differences with which they are hydrolysed under various basic conditions. Yet the mechanistic underpinnings of these rate differences have remained unclear, which has hindered efforts to address the current limitations of this chemistry. Here we show that there are two distinct mechanisms for this hydrolysis: one is base mediated and the other neutral. The former can proceed more than three orders of magnitude faster than the latter, and involves a rate-limiting attack by a hydroxide at a MIDA carbonyl carbon. The alternative ‘neutral’ hydrolysis does not require an exogenous acid or base and involves rate-limiting B–N bond cleavage by a small water cluster, (H2O)n. The two mechanisms can operate in parallel, and their relative rates are readily quantified by 18O incorporation. Whether hydrolysis is ‘fast’ or ‘slow’ is dictated by the pH, the water activity and the mass-transfer rates between phases. These findings stand to enable, in a rational way, an even more effective and widespread utilization of MIDA boronates in synthesis.
Original languageEnglish
Pages (from-to)1067-1075
Number of pages9
JournalNature Chemistry
Volume8
Early online date25 Jul 2016
DOIs
Publication statusPublished - Nov 2016

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