Pyrrole chemistry. XVII. Alkylation of the pyrrolyl ambident anion

Abstract

A series of experiments were carried out to find optimum conditions for C- and N-alkylation of the pyrrolyl ambident anion. While almost total C-alkylation could be obtained, isolation of a single alkylation product was not feasible. However, N-alkylation of pyrrole and several 2-substituted pyrroles was readily achieved by phase transfer catalysis with primary alkyl halides.

Synthesis and spectroscopic studies of some substituted 3-benzoylpyrroles and their tricarbonylchromium complexes

“…bonylchromium complexes were prepared from the parent pyrrole and Cr(C0)6 in refluxing di-n-butyl ether as previously described (9). The N-methyl derivatives of the ligands and complexes were prepared by reaction with dimethyl sulfate using phase transfer catalysis as outlined previously (10). The radical anions were prepared from the N-methyl derivatives using potassium in 1,2-dimethoxyethane (DME) as described in an earlier paper (4).…”

Five‐Membered Heterocycles: Pyrrole and Related Systems

“…N-Alkylation of 255 formed by deprotonation of pyrrole by KOH in DMSO offers a high-yielding route to 1-alkylpyrroles [380], although several more convenient and effective procedures rely on phase transfer conditions using 18-crown-6 as the catalyst, in combination with KOH in anhydrous benzene [381], or with potassium tert-butoxide in diethyl ether [382]. Phase transfer alkylation of pyrrole by alkyl halides with aqueous NaOH in CH 2 Cl 2 in the presence of tetrabutylammonium bromide constitutes a useful alternative [383]. Interestingly, 2,5-dialkylpyrrolyl anions generated in the superbase system KOH-DMSO will instead react at C3 with carbon disulfide, providing a route …”

“…Pyrrolylthallium(I), prepared from pyrrole and thallium(I) ethoxide, can also be utilized for N-alkylation of pyrroles [388], but should perhaps be avoided because of its toxicity. Pyrrolylmagnesium halides, which are easily prepared by the action of alkylmagnesium halides on pyrrole, display more complex reactivity patterns towards most alkylating agents, rendering mixtures of C2 and C3 substituted products, as well as diand tri-alkylpyrroles [383,389]. In contrast, acylation of pyrrolylmagnesium halides is more selective, giving 2-acylpyrroles as the prevailing products [390].…”

Vibrational characterization of poly(1‐methylpyrrole‐ co‐squaric acid) and poly(1‐dodecylpyrrole‐co‐squaric acid) by enhanced Raman spectroscopy

“…The 1-dodecylpyrrole derivative was synthesized by an alkylation reaction via charge-transfer catalysis: 16 Five milliliters of 50% sodium hydroxide aqueous solution was added to a solution of 10 mmol of pyrrole, 11 mmol of 1-bromodocecyl and 1 mmol of tetrabutylammonium bromide in 10 ml of dichloromethane, with external cooling. The mixture was stirred and refluxed for 20 h and then diluted with water and extracted with dichloromethane.…”