Thermodynamic Controlled Regioselective C1-Functionalization of Indolizines with 3-Hydroxyisoindolinones via Brønsted Acid Catalyzed aza-Friedel-Crafts Reaction

A Brønsted acid catalyzed aza-Friedel-Crafts reaction of indolizines with 3-hydroxyisoindolinones has been established, which constructs isoindolinone derivatives bearing a tetrasubstituted stereocenter in good to high yields and enantioselectivities. Notably, this strategy provides a new access to C1-functionalization of indolizines with excellent regioselectivities. Moreover, this intriguing C1-regioselective transformation was induced under thermodynamic control.

Enantioselective synthesis of α-tetrasubstituted (1-indolizinyl) (diaryl)-methanamines via chiral phosphoric acid catalysis

An enantioselective Friedel-Crafts reaction of cyclic α-diaryl N-acyl imines with indolizines catalyzed by a chiral spirocyclic phosphoric acid has been developed. The asymmetric transformation proceeds smoothly to afford α-tetrasubstituted (1-indolizinyl) (diaryl)methanamines in good yields with up to 98% ee under mild conditions.

Chiral Phosphoric Acid-Catalyzed Asymmetric Friedel-Crafts Addition of Indolizine to Cyclic N-Sulfonyl Imine

A highly efficient chiral phosphoric acid-catalyzed enantioselective Friedel-Crafts addition of indolizine to cyclic N-sulfonyl imine has been established. The newly developed protocol, which probably proceeds via a monoactivation reaction pathway, allows the access of enantioenriched sulfonamide functionalized indolizines with excellent yields (up to 99%) and enantioselectivities (up to 99%). Moreover, the synthetic utility of this protocol has been explored with some chemical transformations.

C-O Coupling/[4+2] Cycloaddition Tandem Reactions via Oxidative Dearomatization of BINOLs: Access to Bridged Polycyclic Compounds

Intramolecular C-H activation/C-O coupling, dearomatization, and [4+2] cycloaddition of BINOL units have been well developed in a one-pot approach with maleimide derivatives as the dienophiles. This tandem catalytic system generates a variety of functionalized bridged polycyclic products in a step-economical manner, which greatly enriches the modification methods and strategies for the BINOL skeletons.

Synthesis of Indolizines via Tf2O-Mediated Cascade Reaction of Pyridyl-enaminones with Thiophenols/Thioalcohols

A cost-effective, highly regioselective and metal-free version for the synthesis of indolizine derivatives by means of Tf₂O-mediated cascade reaction of pyridyl-enaminones and thiophenols/thioalcohols under mild reaction conditions has been reported. Diverse electron-rich indolizine derivatives could be obtained in up to 94% yield via the selective 1,4-addition of vinyl iminium triflate tandem cyclization/aromatization, which allowed the simultaneous construction of C-N and C-S/and one example of C-Se bonds.

I2-Promoted In Situ Cyclization-Rethiolation Reaction: Synthesis of 2-Aliphatic- or Aromatic-Substituted Indolizines

An efficient I₂-promoted one-pot one-step three-component reaction for the synthesis of sulfhydryl indolizines from methyl ketones, 2-pyridylacetate derivatives, and sulfonyl hydrazides via an in situ cyclization-rethiolation strategy has been developed. This protocol shows excellent substrate compatibility, including for chain and cyclic aliphatic methyl ketones, natural product pregnenolone acetate, and phosphorus-containing methyl ketones, affording a series of valuable aliphatic-substituted indolizines in good yields.

B2pin2-Mediated Cascade Cyclization/Aromatization Reaction: Facial Access to Functionalized Indolizines

Herein, a B₂pin₂-mediated radical cascade cyclization/aromatization reaction of enaminone with pyridine is described. This strategy provides a practical way for the construction of valuable functionalized indolizines under metal-, external oxidant-, and base-free conditions, which could be compatible with various kinds of functional groups, such as halogen, π-system, heterocycle, ferrocenyl, etc. A preliminary mechanism investigation indicated that the pyridine-boryl radical formed in situ triggered the reaction to occur.

Enantioselective synthesis of α-tetrasubstituted (3-indolizinyl) (diaryl)methanamines via chiral phosphoric acid catalysis

An enantioselective Friedel-Crafts reaction of cyclic α-diaryl N-acyl imines with indolizines catalyzed by a chiral spirocyclic phosphoric acid has been developed. The asymmetric transformation proceeds smoothly to afford α-tetrasubstituted (3-indolizinyl) (diaryl)methanamines in good yields with up to 98% ee under mild conditions.

Fused pyrrolo-pyridines and pyrrolo-(iso)quinoline as anticancer agents

This work emphasizes the synthesis strategies and antiproliferative related properties of fused pyrrolo-pyridine (including indolizine and azaindoles) and pyrrolo-(iso)quinoline derivatives recently reported in literature.

Chiral Phosphoric Acid Catalyzed Desymmetrization of Cyclopentendiones via Friedel-Crafts Conjugate Addition of Indolizines

An organocatalytic highly diastero- and enantioselective Friedel-Crafts conjugate addition of indolizines to prochiral cyclopentenediones has been successfully developed. This desymmetric transformation provides a direct access to the desired indolizine-substituted cyclopentanediones in yields of 62-91% and excellent stereoselectivities. The utility of the approach was demonstrated by diverse late-stage functionalizations through reduction or oxidation. Importantly, the direct sp² C-H functionalization with nitromethane in one-pot process resulted in the indolizine-linked axially chiral styrene bearing a remote chiral center.

Recent advances in the synthesis of indolizine and its derivatives by radical cyclization/cross-coupling

Indolizine is a nitrogen-containing heterocycle that has a variety of potential biological activities, and some indolizine derivatives with excellent fluorescence properties can even be used as organic fluorescent molecules for biological and material applications. Thus, many approaches for their synthesis have been developed. Among them, radical-induced synthetic approaches are receiving increasing attention owing to their unique advantages, such as efficient heterocycle construction, efficient C-C or C-X bond construction, and high atom- and step-economy. This review systematically examines the current and latest synthetic strategies using radical species or radical intermediates for synthesizing indolizines and their derivatives. This review is classified into two parts based on the type of building blocks used for indolizine ring construction and the type of radical trigger for indolizine derivative construction. We anticipate that this review will provide a deep understanding of this topic, and ultimately help researchers to develop novel approaches for the synthesis of indolizine and its derivatives.