Convenient Synthesis of Alkenyl-, Alkynyl-, and Allenyl-Substituted Imidazo[1,2-a]pyridinesvia Palladium-Catalyzed Cross-Coupling Reactions

Stereodivergent access to non-natural α-amino acids via enantio- and Z/E-selective catalysis

The precise control of Z and E configurations of the carbon-carbon double bond in alkene synthesis has long been a fundamental challenge in synthetic chemistry, even more pronounced when simultaneously striving to achieve enantioselectivity [(Z,R), (Z,S), (E,R), (E,S)]. Moreover, enantiopure non-natural α-amino acids are highly sought after in organic and medicinal chemistry. In this study, we report a ligand-controlled stereodivergent synthesis of non-natural α-quaternary amino acids bearing trisubstituted alkene moieties in high yields with excellent enantioselectivity and Z/E selectivities. This success is achieved through a palladium/copper-cocatalyzed three-component assembly of readily available aryl iodides, allenes, and aldimine esters by simply tuning the chiral ligands of the palladium and copper catalysts.

Transition Metal Catalyst-Free C-3 Sulfonylmethylation of Imidazo[1,2-a]pyridines with Glyoxylic Acid and Sodium Sulfinates in Water

Herein, we describe an efficient and benign protocol for direct C-3 sulfonylmethylation of imidazo[1,2-a]pyridines with glyoxylic acid and sodium sulfinates. Various sulfonylmethylated imidazo[1,2-a]pyridines were synthesized in water under transition metal catalyst-free conditions. This multicomponent reaction featured available substrates, good functional group tolerance, moderate to excellent yields, and mild reaction conditions.

An electrolyte- and catalyst-free electrooxidative sulfonylation of imidazo[1,2-a]pyridines

An electrolyte- and catalyst-free electrooxidative C–H activation reaction is developed to afford 3-sulfonylated imidazo[1,2-a]pyridines in good to excellent yields.

8-Alkynyl-3-nitroimidazopyridines display potent antitrypanosomal activity against both T. b. brucei and cruzi

An antikinetoplastid pharmacomodulation study was done at position 8 of a previously identified pharmacophore in 3-nitroimidazo[1,2-a]pyridine series. Twenty original derivatives bearing an alkynyl moiety were synthesized via a Sonogashira cross-coupling reaction and tested in vitro, highlighting 3 potent (40 nM ≤ EC₅₀ blood stream form≤ 70 nM) and selective (500 ≤ SI ≤ 1800) anti-T. brucei brucei molecules (19, 21 and 22), in comparison with four reference drugs. Among these hit molecules, compound 19 also showed the same level of activity against T. cruzi (EC₅₀ amastigotes = 1.2 μM) as benznidazole and fexinidazole. An in vitro comet assay showed that nitroaromatic derivative 19 was not genotoxic. It displayed a low redox potential value (-0.68 V/NHE) and was shown to be bioactivated by type 1 nitroreductases both in Leishmania and Trypanosoma. The SAR study indicated that an alcohol function improved aqueous solubility while maintaining good activity and low cytotoxicity when the hydroxyl group was at position beta of the alkyne triple bond. Hit-compound 19 was also evaluated regarding in vitro pharmacokinetic data: 19 is BBB permeable (PAMPA assay), has a 16 min microsomal half-life and a high albumin binding (98.5%). Moreover, compound 19 was orally absorbed and was well tolerated in mouse after both single and repeated administrations at 100 mg/kg. Its mouse plasma half-life (10 h) is also quite encouraging, paving the way toward further efficacy evaluations in parasitized mouse models, looking for a novel antitrypanosomal lead compound.

Microwave assisted novel and regioselective functionalization of imidazopyridines with chromene acetals and β-nitrostyrenes

A facile synthesis of novel functionalized imidazopyridines has been accomplished through the condensation of imidazopyridines with chromene hemiacetals or β-nitro styrenes with high regioselectivity and excellent yields in the presence of a catalytic amount of PTSA or InCl₃.

One-pot synthesis of 2-phenylimidazo[1,2-α]pyridines from acetophenone, [Bmim]Br(3) and 2-aminopyridine under solvent-free conditions

One-pot synthesis of 2-phenylimidazo[1,2-α]pyridines from acetophenone, [Bmim]Br₃ and 2-aminopyridine under solvent-free conditions in the presence of Na₂CO₃, gave the corresponding 2-phenylimidazo[1,2-α]pyridines in excellent yields ranging from 72% to 89%.

How easy are the syntheses of allenes?

This short review highlights some of the recent important developments on the synthesis of allenes and its applications on the synthesis of some allenic natural products and allenic-based optoelectronic materials.