Ethynylation of 2-(furan-2-yl)- and 2-(thiophen-2-yl)pyrroles with acylbromoacetylenes in the Al2O3 medium: relative reactivity of heterocycles

Undirected, Selective Csp2-H Alkynylation of Five-membered Heteroarenes

“…thienylpyrroles. [70] The experimental results evidenced the higher reactivity of pyrroles ring when compared to furan and thiophene derivatives, and considering the mechanistic pathway previously suggested they are in agreement with the lower ionization potential of then pyrrole ring in respect to that of the other two heteroarenes. In fact, only the alkynylated products deriving from the alkynylation of the pyrrole nucleus were obtained when 2-thienylpyrroles was used as heteroarenes.…”

“…In the last two decades Trofimov's research team reported a series of interesting papers on the development of solvent-free procedures for the direct alkynylation of pyrroles with 1acylbromoacetylenes that made use of aluminum oxide (Al2O3) and other metal oxides as a solid active reaction medium. [68][69][70] The experimental procedures simply involved mixing the two reagents and metal oxide, and grinding the solid mixture thus obtained in a mortar at room temperature.…”

Stereoselective Synthesis of Acylethenyl Tetrahydropyridino- and Deazepanopyrrolo[1,2-c]imidazolidines via Annulation of Cyclic Imines with Acylethynylpyrroles

“…Acylethynylpyrroles 1 were obtained from the corresponding pyrroles and acylbromoacetylenes according to the described procedure. 20a The analytical data of acylethynylpyrroles 1a , c , d , h 20a 1b , 20b 1e , 20c 1f , 20d 1g , 20e and 1i 20f were in accord with literature values. Cyclic imines 2a , b , 22 2c – e and 4a – e 23 were prepared by literature methods.…”

Recent Strides in the Transition Metal-Free Cross-Coupling of Haloacetylenes with Electron-Rich Heterocycles in Solid Media

“…The generation of radical-ions during this process was evidenced from ESR signals observed in the reaction of 1-vinyl-2-phenyl-3-amylpyrrole (1, R 1 = CH=CH 2 , R 2 = Ph, R 3 = C 5 H 11 ) with iodopropiolaldehyde in solid K 2 CO 3 . The reaction of 2-(furan-2-yl)-(4) and 2-(thiophen-2-yl)pyrroles 5 with acylbromoacetylenes 6a-c was carried out according to the similar procedure: the reactants (1:1 molar ratio) were ground with a 10-fold excess of Al 2 O 3 at room temperature for 1 h [54]. The major direction of this ethynylation of 2-(furan-2-yl)pyrroles 4 was the formation of 2-acylethynyl-5-(furan-2-yl)pyrroles 7 (Scheme 4), while the alternative 2-acylethynyl-5-(pyrrol-2-yl)furans 8 were minor products (7:8 =~5-7:1).…”