Alkylpyrroles salts

N-Acylation is readily carried out by reaction of the alkaU metal salts with the appropriate acid chloride. C-Acylation of pyrroles carrying negative substituents occurs in the presence of Friedel-Crafts catalysts. Pyrrole and alkylpyrroles can be acylated noncatalyticaHy with an acid chloride or an acid anhydride. The formation of trichloromethyl 2-pyrryl ketone [35302-72-8] (20, R = CCI3) is a particularly useful procedure because the ketonic product can be readily converted to the corresponding pyrrolecarboxyUc acid or ester by treatment with aqueous base or alcohoHc base, respectively (31). 

Pyrrole and alkylpyrroles can be acylated by heating with acid anhydrides at temperatures above 100 °C. Pyrrole itself gives a mixture of 2-acetyl- and 2,5-diacetyl-pyrrole on heating with acetic anhydride at 150-200 °C. iV-Acylpyrroles are obtained by reaction of the alkali-metal salts of pyrrole with an acyl halide. AC-Acetylimidazole efficiently acetylates pyrrole on nitrogen (65CI(L)1426). Pyrrole-2-carbaldehyde is acetylated on nitrogen in 80% yield by reaction with acetic anhydride in methylene chloride and in the presence of triethylamine and 4-dimethylaminopyridine (80CB2036). 

Alkylation of N-heteroeycKc compoumb. Pyrrole can be N-alkylated sali ractorily by conversion to pyrrylthallium(I) by reaction with thallous ethoxide. This is a relatively stable solid the structure is uncertain. Reaction of this salt with an excess of an alkyl halide (or an alkyl tosylate) for 1-32 hr. at 20-60° gives N-alkylpyrroles in good yield. Alkylation of pyrrylmagnesium bromide gives isomeric 2- and 3-alkylpyrroles as the major products. 

Triazoles and Benzotriazoles. - The alkenediazonium salt (431 Ar = P-NO2C6H4) is converted into the triazoles (432 R = H or alkyl) by the action of amines. Anodic oxidation of the oxime phenylhydrazone of benzil, HON=CPhCPh=NNHPh, gives the AA-oxide (433). The alkenyl-triazolines (434 R = H or alkyl) afford the aziridines (435) on flash vacuum py roly sis.Photolysis of the 4-alkylaminotriazoles (436 R = alkyl) yields 2-alkylpyrroles rather than the expected 3-alkyIpyrroles. The... 

Addition of Alkyl Groups. Katrizky reported that in the presence of bismuth(lll) chloride-metallic aluminum, alkyl (as well as allyl) halides react with A-(alkylamino)benzotriazoles at 20°C in THF-water to give the corresponding homoalkylated amines in high yields (Eq. 11.48). Competitive addition of CCI3 anions to N-alkyl-pyridinium salts was studied in a two-phase system of chloro-form/concentrated aqueous NaOH and in a homogeneous medium. Aminomethylation of 1-alkylpyrroles by aqueous formaldehyde and dimethylamine hydrochloride, followed by reaction with iodomethane, affords the l-alkyl-2,5- A[(trimethylammonio)methyl]pyrrole diiodide... 

On treatment with Vilsmeier salts, V-alkylpyrroles formylate in the expected 2-position unless the alkyl group is bulky, in which case formylation at the 3-position is preferred. The 2-substituted pyrroles tend to formylate at the 5-position, and 3-substituted pyrroles formylate at the 2- and 5-position with low regioselectivity. 

Potassium reacts readily with pyrrole and alkylpyrroles in boiling toluene sodium is much less reactive, and lithium unreactive. Pyrrole salts of all three metals are readily formed from solutions of the metals in liquid ammonia . ... 

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