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How Big is the Pinacol Boronic Ester as a Substituent?
Author(s) -
Fasano Valerio,
McFord Aidan W.,
Butts Craig P.,
Collins Beatrice S. L.,
Fey Natalie,
Alder Roger W.,
Aggarwal Varinder K.
Publication year - 2020
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.202007776
Subject(s) - steric effects , pinacol , moiety , chemistry , planarity testing , stereochemistry , substituent , a value , diol , ligand cone angle , boronic acid , ligand (biochemistry) , organic chemistry , catalysis , crystallography , receptor , materials science , conical surface , composite material , biochemistry
The synthetically versatile pinacol boronic ester group (Bpin) is generally thought of as a bulky moiety because of the two adjacent quaternary sp 3 ‐hydribized carbon atoms in its diol backbone. However, recent diastereoselective reactions reported in the literature have cast doubt on this perception. Reported herein is a detailed experimental and computational analysis of Bpin and structurally related boronic esters which allows determination of three different steric parameters for the Bpin group: the A‐value, ligand cone angle, and percent buried volume. All three parameters suggest that the Bpin moiety is remarkably small, with the planarity of the oxygen‐boron‐oxygen motif playing an important role in minimising steric interactions. Of the three steric parameters, percent buried volume provides the best correlation between steric size and diastereoselectivity in a Diels–Alder reaction.