Computational assessments of diastereoselective [4+2] cycloaddition and 1,3-borotopic shift of a dearomatized tertiary boronic ester intermediate: reactivities explained through transition-state distortion energies

Abstract

Interception of dearomatized tertiary boronic ester in a diastereoselective [4+2] cycloaddition or 1,3-borotopic shift in the presence or absence of “naked” Li+, understanding reactivities by activation/strain model, were evaluated by DFT calculations.

How Big is the Pinacol Boronic Ester as a Substituent?

“…To our surprise, the observed diastereoselectivities suggested that the Bpin group is considerably less sterically demanding than simple α‐branched alkyl groups and that its apparent size, at least in terms of our selectivity model, lay in the order: cyclohexyl ≫ phenyl > Bpin > cyclopropyl > primary alkyl. Our experimental results were also supported by a computational analysis [11] . These unexpected results, along with the contradictory interpretations of experimental observations in the literature, convinced us that a comprehensive investigation of the size of the synthetically valuable Bpin group was needed.…”

“…Our experimental results were also supported by a computational analysis. [11] These unexpected results, along with the contradictory interpretations of experimental observations in the literature, convinced us that a comprehensive investigation of the size of the synthetically valuable Bpin group was needed. Herein, we report a broad investigation using experimental (low temperature quantitative 13 C NMR) and computational (DFT and common steric parameters) approaches to answer the question: how big is Bpin?…”