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How Big is the Pinacol Boronic Ester as a Substituent?
Valerio Fasano1, Aidan W McFord1, Craig P Butts1
1School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, UK.
Angewandte Chemie (International Ed. in English)
|September 1, 2020
Summary
The pinacol boronic ester (Bpin) group is surprisingly small, challenging its common perception as bulky. Its reduced steric hindrance, particularly due to its planar structure, impacts chemical reactions like Diels-Alder.
Area of Science:
- Organic Chemistry
- Stereochemistry
- Computational Chemistry
Background:
- The pinacol boronic ester (Bpin) group is widely used in organic synthesis.
- Bpin is often perceived as a sterically demanding group due to its structure.
Purpose of the Study:
- To quantitatively assess the steric properties of the Bpin group.
- To investigate the relationship between steric parameters and diastereoselectivity in reactions.
Main Methods:
- Experimental determination of steric parameters (A-value, ligand cone angle, percent buried volume).
- Computational analysis of Bpin and related boronic esters.
- Correlation analysis with diastereoselectivity in Diels-Alder reactions.
Main Results:
- All three measured steric parameters indicate that Bpin is a small moiety.
- The planar oxygen-boron-oxygen motif significantly minimizes steric interactions.
- Percent buried volume best correlates steric size with Diels-Alder diastereoselectivity.
Conclusions:
- The perceived bulkiness of the Bpin group is inaccurate; it is sterically small.
- The planarity of the O-B-O unit is crucial for its reduced steric profile.
- Percent buried volume is a key metric for predicting stereochemical outcomes in reactions involving Bpin.
Keywords:
A-valuesboronic estersconformational analysisdensity-functional calculationssteric hinderanceMore Related Videos
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