Imine as a Linchpin Approach for Distal C(sp2)–H Functionalization
semanticscholar(2020)
摘要
Despite
the widespread applications of C–H functionalization, controlling site
selectivity remains a significant challenge. Covalently attached directing
group (DG) served as an ancillary ligand to ensure proximal ortho-,
distal meta- and para-C-H functionalization over the
last two decades. These covalently linked DGs necessitate two extra steps for a
single C–H functionalization: introduction of DG prior to C–H activation and
removal of DG post-functionalization. We introduce here a transient directing
group for distal C(sp2)-H
functionalization via reversible
imine formation. By overruling facile proximal C-H bond
activation by imine-N atom, a
suitably designed pyrimidine-based transient directing group (TDG) successfully
delivered selective distal C-C
bond formation. Application of this transient directing group strategy for
streamlining the synthesis of complex organic molecules without any necessary
pre-functionalization at the distal position has been explored.
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