A practical approach to the synthesis of [2‐(trimethylsilyl)ethynyl]pyrazoles was developed through condensation of hydrazines with enynones that are easily accessible frombis(trimethylsilyl)acetylene and arylacetyl chlorides. Optimized conditions for reactions with monoarylhydrazines permit the chemoselective formation of 5‐alkynylpyrazoles in high yields (48–94 %). When monoalkylhydrazines or the parent hydrazine is used, mixtures of 3‐ and 5‐alkynylpyrazoles are formed in 73–79 % yields. The method uses inexpensive starting materials and can be applied to a variety of substrates, which makes it convenient for the synthesis of alkynylpyrazoles.
The combination of two privileged motifs, that is, indoline and the constrained peptidomimetic piperazine‐2,5‐dione, within one tricyclic structure resulted in a scaffold that is abundant in nature but surprisingly scarce in the domain of synthetic bioactive molecules. Utilizing the power of the isocyanide‐based Joullié–Ugi reaction followed by postcondensation cyclization, we synthesized such compounds with four elements of diversity in good yields from readily available precursors. The compounds are constrained peptidomimetics distinctly encumbered in a steric sense and have a pronounced three‐dimensional character, which is a highly desirable feature in modern drug design.
Condensation of enynones readily available from cheap starting material with pyrazolamines provides easy access to fluorescent 7-(trimethylsilylethynyl)pyrazolo[1,5-a]pyrimidines. The reaction is straightforward, does not require the use of any additional reagents or catalysts, and can be performed without inert atmosphere. Various substituents and functional groups in both enynone and pyrazolamine are tolerated. The presented method features full regioselectivity, high isolated yields, and simplicity of both setup and product purification. Fluorescent properties of the obtained pyrazolopyrimidines were studied.
Sterically demanding indolenines were employed as cyclic imine substrates in the Joullié–Ugi reaction with diverse isocyanides and carboxylic acids resulting in a new type of conformationally constrained indoline‐based peptidomimetic compounds.
The regioselectivity of the reaction between unsymmetric thioureas and maleic acid derivatives has been studied, and general regularities have been established.
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