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MIDA boronates are hydrolysed fast and slow by two different mechanisms.

Gonzalez, JA and Ogba, OM and Morehouse, GF and Rosson, N and Houk, KN and Leach, AG and Cheong, PH-Y and Burke, MD and Lloyd-Jones, GC (2016) MIDA boronates are hydrolysed fast and slow by two different mechanisms. Nature Chemistry, 8 (11). pp. 1067-1075. ISSN 1755-4330

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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 (18)O 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.

Item Type: Article
Uncontrolled Keywords: 03 Chemical Sciences
Subjects: Q Science > QD Chemistry
Divisions: Pharmacy & Biomolecular Sciences
Publisher: Nature Publishing Group
Related URLs:
Date Deposited: 01 Nov 2016 12:21
Last Modified: 07 Sep 2017 23:49
DOI or Identification number: 10.1038/nchem.2571
URI: http://researchonline.ljmu.ac.uk/id/eprint/4716

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