Assembly of Functionalized 4‐Alkynylisoxazoles by Palladium‐Catalyzed Three‐Component Cascade Cyclization/Alkynylation

Abstract

A novel N‐heterocyclic carbene (NHC)‐palladium‐catalyzed three‐component cascade cyclization/alkynylation for the synthesis of structurally diverse 4‐alkynylisoxazoles was efficiently developed in ionic liquids. The operational simplicity, without additives, no additional ligands, and 0.5 mol % catalyst loading under air are some of the attractive features of this present protocol.

Palladium‐Catalyzed Cascade Cyclization/Alkynylation Reactions

“…Very recently, we also developed an effective and green N ‐heterocyclic carbene (NHC)‐palladium‐catalyzed three‐component cascade cyclization/alkynylation of O ‐methyl oxime ( 14 ), secondary amines, and alkynes in ionic liquids (Scheme ) . A variety of O ‐methyloximes ( 14 ) and several secondary amines were well tolerated in this chemical transformation, and furnished the corresponding 4‐alkynylisoxazoles ( 18 ) in moderate to good yields.…”

Recent advances in metal catalyzed or mediated cyclization/functionalization of alkynes to construct isoxazoles

“…Satisfyingly, a highly regioselective palladium-catalyzed three-component cascade cyclization/alkynylation of alkynone O-methyloximes (14), propargyl p-toluenesulfonate (15), and secondary amines (16) was efficiently developed in ionic liquids (Scheme 7). 25 A whole variety of conventional solvents such as DMSO, DMF, toluene, and DCE were observed; however, all of them were found to be less effective. Delightfully, the ionic liquid [Bmim]Cl (1-butyl-3-methylimidazolium chloride) was found to be the best solvent for this transformation.…”

Synthesis of Isoselenazoles and Isothiazoles from Demethoxylative Cycloaddition of Alkynyl Oxime Ethers

“…3-([1,1′-Biphenyl]-4-yl)-1-phenylprop-2-yn-1-one O-Methyl Oxime (1bb). 15 Petroleum ether as the eluent; white solid (342.1 mg, 55% yield); mp 95−97 °C; 1 H NMR (400 MHz, CDCl 3 ) δ 7.95 − 7.94 (m, 2H), 7.71−7.69 (m, 2H), 7.64−7.62 (m, 4H), 7.49−7.39 (m, 6H), 4.17 (s, 3H).…”