gram scale via kinetic resolution of excess
racemic bromochloromethyl boronic acid
pinacol ester by deprotonated thiourea 4
to enable further synthetic and mechanistic
studies (Fig. 1E). Upon lithiation of precata-
lyst6awith LiHMDS, shifts were observed
in the infrared (IR) frequencies of both the
isothiourea N–C–N stretch (1596 cm–^1 to
1555 cm–^1 ,d=–41 cm–^1 ) and the amide C–O
stretch (1658 cm–^1 to 1618 cm–^1 ,d=–40 cm–^1 ),indicative of perturbations to both func-
tional groups (Fig. 2A). These shifts were
fully reversible by addition of one equivalent
of HCl. The observed IR spectral changes were
interpreted as being due to deprotonation ofSCIENCEscience.org 5 NOVEMBER 2021•VOL 374 ISSUE 6568 755
Fig. 3. Synthetic application.(A) Substrate
scope of rearrangement catalyzed byLi-6a. Yield
values refer to NMR yields relative to internal
standard. The absolute configuration of
rearrangement products 5 was determined
by x-ray crystallographic analysis of7land
of the secondary boronic ester generated by
addition of phenethylmagnesium bromide
to5l(see supplementary materials). (B) Tele-
scoped carbon-chlorine bond elaborations of
rearrangement products with organometallic
nucleophiles. Yield values refer to isolated
yields over two steps. (C) Carbon-boron bond
elaborations of secondary boronic ester
products. Yield and ee values refer to isolated
yields over one step and enantiomeric excess
of products 8 , respectively; e.s. is the reaction
enantiospecificity based on the ee observed
for the products 7 from the catalytic reaction;
rsm is recovered starting material. See
supplementary materials for reaction
conditions. Ph, phenyl; Cbz, benzyloxycarbonyl.
*Lithium boronate substrate prepared with
additional equivalents of CH 2 Cl 2 .†Yield
refers to NMR yield.‡Reactions carried out
at 0.5-mmol scale. §Yield refers to isolated yield
over three steps.RESEARCH | REPORTS