Reactions of 5-(Trialkyl)silylpent-1-en-4-yn-3-ones with Hydrazines: Original Synthetic Routes to Luminescent Substances Containing Azole Motifs

On the basis of the selective reactions of hydrazines with trialkylsilyl-substituted cross-conjugated enynones (pent-1-en-4-yn-3-ones) as fundamental building blocks, this work presents the developed common methodology for the synthesis of polysubstituted luminescent derivatives of acetylenic pyrazolines, pyrazoles, and combined polyheterocycles containing structural fragments from pyrazolines, isoxazoles, thiophenes, thiazoles, benzo[d]thiazoles, and benzo[d]imidazoles. In reactions with hydrazine and its monosubstituted aromatic and heteroaromatic derivatives, the mentioned pent-1-en-4-yn-3-ones, containing Me3Si, Et3Si, and t-BuMe2Si groups at the triple bond, give 3-(trialkylsilyl)ethynylpyrazolines. Following stages of desilylation and 1,3-dipolar cycloaddition with nitrile oxides, the 3-(trialkylsilyl)ethynylpyrazolines provide the formation of combined polyheterocyclic derivatives. Thus, a one-pot synthetic route to pyrazoline-containing isoxazoles from cross-conjugated enynones, arylhydrazines, and α-chlorobenzaldoximes has been developed. Some aspects of cyclocondensation mechanism and luminescent properties of synthesized azoles derivatives were examined.