Transient-Ligand-Enabled ortho-Arylation of Five-Membered
Heterocycles:Facile Access to Mechanochromic Materials
Bijin Li, Kapileswar Seth, Ben Niu, Lei Pan, Huiwen Yang,and Haibo Ge*
Abstract: Reported herein is the first example of adirect
arylation of heteroarenes by atransient-ligand-directed strat-
egy without the need to construct and deconstruct the directing
group.Awide range of heteroarenes undergoes the coupling
with diverse aryl iodides to assemble alarge library of highly
selective and functionalized3-arylthiophene-2-carbaldehydes.
This route provides an opportunity to rapidly access new
mechanofluorochromic materials.Moreover,anovel strategy
for mechanochromic luminogens with chromism trends of red-
and blue-shifts has been disclosed for the first time by facile
functional-group modifications to acommon structural core.
The b-aryl-substituted five-membered heterocyclic motif is
aprivileged scaffold in organic functional materials,bioactive
compounds,and pharmaceuticals (Scheme 1).
b-aryl-substituted five-membered heterocyclic carbonyl com-
pounds can be obtained by condensation reactions and
classical transition metal catalyzed C
syntheses and regioselectivity problems associated with these
protocols significantly restrict/impede rapid access to struc-
turally diverse b-aryl-substituted five-membered heterocyclic
Despite the recent advancement of
transition metal catalyzed direct C
Harylation of hetero-
arenes,the development of anovel transition-metal catalytic
system that can selectively arylate otherwise less reactive C
Hbonds on five-membered heterocycles is very important
from both scientific and practical aspects.
Hbond arylation of thiophenes/
pyrroles with haloarenes preferentially occurs at the positions
a to the sulfur/nitrogen atom (C2 and/or C5) because of the
chemical reactivity of the thiophene/pyrrole ring.
selective and preferential arylation at the positions b to the
sulfur/nitrogen atom has rarely been documented, thus
encouraging the design of an efficient strategy to accomplish
arylation at the less reactive C
Hbond on heteroarenes.
Recently,the use of atransient ligand as the directing
group has emerged as apromising strategy in the field of
Hactivation. Theligand can bind to the substrate
and then coordinate to the metal center in areversible
fashion, and thus bears inherent advantages of ready instal-
lation and easy removal without affecting the functionality of
Thedirect arylation of aliphatic aldehydes
and benzaldehydes by atransient-ligand-directed strategy has
been reported (Schemes 2a,b).
To the best of our knowl-
edge,the direct arylation of five-membered heterocyclic
Scheme 1. Selected examples of pharmaceuticals, natural products,
and organic functional material molecules containing b-aryl-substi-
tuted five-membered heterocyclic motifs.
Scheme 2. Direct arylation of aliphatic aldehydes,benzaldehydes, and
heteroaryl-aldehydes by atransient-ligand-directed strategy without the
construction and deconstructionofadirecting group.
[*] B. Li, K. Seth, B. Niu, L. Pan, H. Yang, Prof. Dr.H.Ge
Department of Chemistry and ChemicalBiology,Indiana University-
Purdue University Indianapolis
Supportinginformation and the ORCID identification number(s) for
the author(s) of this article can be found under:
3459Angew.Chem. 2018, 130,3459 –3463 2018 Wiley-VCH VerlagGmbH &Co. KGaA,Weinheim