A new method for the acylation of pyrroles

Synthesis of dipyrrins bearing chirality adjacent to the conjugated skeleton — Electron-poor pyrroles exhibit dramatically reduced nucleophilicity

“…Unfortunately treatment of 13 with TFA and TFAA, under the conditions that had been successful for the synthesis of 2, gave only the pyrrolo-[3,2-f]indole 18 where presumably mono-trifluoracylation had been followed by acid-catalyzed intramolecular condensation (Scheme 4). [32][33][34] Since 18 exhibits indolic, rather than pyrrolic, reactivity traits, and because 18 does not feature the required prochiral signature, we sought an alternative route for the synthesis of 12.…”

Five‐Membered Heterocycles: Pyrrole and Related Systems

“…Although attempts to rationalize these differences in regioselectivity in terms of kinetic, steric or electronic factors have been made, no clear conclusions could be drawn [315]. A new contribution to this field allows selective a-acylation of 1-(p-toluenesulfonyl)pyrroles with carboxylic acids and TFAA, presumably involving mixed anhydrides as the acylating agents [319]. Friedel-Crafts acylation of 3-alkyl-1-(phenylsulfonyl)pyrroles with acetic anhydride also proceeds with pronounced Such condensation reactions eventually lead to the formation of porphyrins (Scheme 4.58) [321,322], along with other oligomeric or polymeric products [323], for instance so-called N-confused porphyrins, which are porphyrin isomers featuring a pyrrole unit linked through its a and b 0 positions [324][325][326][327].…”

Selective Synthesis of β‐Alkylpyrroles

“…In contrast to the b-selective acylation observed in the first step, alteration of AlCl 3 into BF 3 ·OEt 2 drastically changes the orientation, thus leading to a-selective acylation. [27,28] A proper choice of a Lewis acid is thus highly important for the strategy B to obtain b-acylpyrroles 15 selectively. The strategy is effective, especially for the synthesis of b-alkylpyrroles 14 cf bearing carboxyl, hydroxy and ester groups (Scheme 10).…”