Conspectus
Catalytic atroposelective syntheses
of axially chiral compounds
have stimulated extensive interest in multiple communities, such as
synthetic chemistry, biochemistry, and materials science, because
of the intriguing characteristics of atropisomerism. In particular,
atropisomeric indole derivatives, which contain a kind of five-membered
heterocyclic framework, are widely distributed in a number of natural
alkaloids, biologically relevant compounds, chiral ligands, and chiral
organocatalysts. Hence, the catalytic atroposelective synthesis of
indole derivatives bearing axial chirality is of considerable importance
and has become an emerging focus of research. However, there are substantial
challenges associated with the atroposelective synthesis of indole
derivatives, including remote ortho-substituents
around the chiral axis, a lower barrier for rotation, and a weaker
configurational stability than that of atropisomeric six-membered
biaryls. Therefore, the development of effective strategies toward
the catalytic atroposelective synthesis of indole derivatives has
become an urgent task.
In order to tackle these challenges and
to accomplish the task,
our group devised a unique strategy of designing indole-derived platform
molecules and developing organocatalytic enantioselective transformations
of such platform molecules to synthesize atropisomeric indole derivatives;
asymmetric organocatalysis has tremendous advantages and was the research
area recognized by the Nobel Prize in Chemistry in 2021. This Account
summarizes our endeavors in the organocatalytic atroposelective synthesis
of indole derivatives bearing axial chirality. In brief, we devised
and developed a series of indole-derived platform molecules, such
as indolylmethanols, (hetero)aryl indoles, oxindole-based styrenes, N-aminoindoles, and indole-based homophthalic anhydrides,
by introducing different functional groups onto the indole ring to
achieve new reactivity and modulate the reactive site of the indole
ring. As a result, these indole-derived platform molecules possess
versatile and unique reactivity and are capable of undergoing a variety
of organocatalytic enantioselective transformations for preparing
structurally diversified indole derivatives with axial chirality.
We used these strategies to accomplish the atroposelective synthesis
of plenty of indole derivatives with axial chirality, including (hetero)aryl
indoles, alkene-indoles, oxindole-based styrenes, N-pyrrolylindoles, and isochromenone-indoles. In addition, we gave
a thorough and detailed understanding of the designed reaction by
investigating the reaction pathway and activation mode. More importantly,
we studied the biological activity of some products and performed
catalyst design on the basis of atropisomeric indole moieties, which
are helpful for disclosing more applications of indole derivatives
bearing axial chirality.
In the future, the organocatalytic
atroposelective synthesis of
indole derivatives bearing axial chirality will indubitably remain
a frontier topic in the...