Alkylpyrroles methyl groups

Partial rate factors, relative to pyrrole, for trifluoroacetylation at the 5-position of some 2-alkylpyrroles are Me, 23.8 Et, 24.8 r-Bu, 24.8 [72JCS(P2)71]. Thus, the activating effect of a 2-alkyl group is far lower than that found in furan and thiophene, and this is confirmed in Vilsmeier formylation and acetylation of pyrroles where 2-methyl activates by factors of 15 and 42, respectively [77G339, 77JCS(P2)1284],... 

The fact that the percentage of jS-aldehydes from Vilsmeier formylation of N-alkylpyrroles increases from M-methyl- to N-(f-butyl)pyrrole can be explained by the increasing steric shielding of the a-positions by an N-alkyl group in the same sequence (70JCS(C)2563) (Scheme 23). 

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... 

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