enantioselective 1,2-boronate rearrangements
using an unexpected catalyst, and its appli-
cation to the synthesis of molecules featuring
a diverse range of trisubstituted stereocenters
(Fig. 1C).
Numerous approaches toward the synthe-
sis of stereodefined alkylboronic esters have
leveraged rearrangement strategies, drawing
from the broad generality of 1,2-boronate re-
arrangements toward various classes of migrat-
ing groups, leaving groups, and boron ligands.
In addition to Matteson’s seminal work using
chiral diol auxiliaries, Aggarwal and co-workers
have developed stoichiometric chiral lithiumcarbenoid reagents that enable the enantio-
selective synthesis of pinacol boronic ester
products via stereospecific formation and re-
arrangement of chiral boronate derivatives
( 12 – 14 ). Morken and others have reported ro-
bust, highly enantioselective catalytic rear-
rangements of prochiral alkenylboronatesSCIENCEscience.org 5 NOVEMBER 2021•VOL 374 ISSUE 6568 753
Fig. 1. Concepts for controlling 1,2-boronate rearrangements and reaction
optimization.(A) Stereochemical outcomes of 1,2-boronate rearrangements.
M, metal; X, leaving group. (B) Diastereoselective Matteson homologation using a
chiral diol auxiliary on boron. Nu, nucleophile. (C) Proposed general three-step
strategy for the construction of tertiary stereocenters from boronic esters,
dichloromethane, and organometallic nucleophiles. Pin, pinacolato. (D) Reaction
optimization and discovery of lithium-isothiourea-boronate catalystLi-6a.
Reactions were run at 0.125-mmol scale. Yield values reflect product
quantification by gas chromatography analysis relative to an internal standard.
nBu andtBu, normal andtert-butyl; Et, ethyl; Me, methyl. (E) Gram-scale
synthesis and x-ray crystal structure of isothiourea-boronate precatalyst6a.
Hydrogen atoms have been removed for presentation.RESEARCH | REPORTS