Catalyst-Free Annulation of Acylethynylpyrroles with 1-Pyrrolines: A Straightforward Access to Tetrahydrodipyrrolo[1,2-a:1′,2′-c]imidazoles

Abstract

Acylethynylpyrroles undergo facile (rt, MeCN or MeOH, 24–72 h) catalyst-free annulation with 1-pyrrolines to afford acylmethylenetetrahydrodipyrrolo­[1,2-a:1′,2′-c]­imidazoles in up to 93% yield and 90% E-stereoselectivity of the olefin moiety.

Contributing to Biochemistry and Optoelectronics: Pyrrolo[1′,2′:2,3]imidazo[1,5-a]indoles and Cyclohepta[4,5]pyrrolo[1,2-c]pyrrolo[1,2-a]imidazoles via [3+2] Annulation of Acylethynylcycloalka[b]pyrroles with Δ1-Pyrrolines

“…The above experimental data evidence that, like in the previous work [ 23 ], the nucleophilic attack of the pyrroline nitrogen at the triple bond plays a key role here. The proton transfer from the pyrrole NH moiety to the vinyl carbanionic center in intermediate A delivers pyrrolate-centered intermediate B .…”

“…Recently [ 23 ], we have serendipitously found that as a convenient platform for the construction of a dipyrrolo[1,2- a :1′,2′- c ]imidazole core, acylethynylpyrroles, readily available from the Al 2 O 3 -promoted cross-coupling of acylbromoacetylenes with pyrroles [ 24 ], can be successfully employed. The similar condensed heterocyclic systems are of high medicinal relevance as they are the principal structural units of compounds with antiviral properties [ 1 , 2 , 3 ].…”

Benzo[1,4]diazocinone/Pyrrole Ensembles via the Catalyst‐Free Insertion of Pyrrolylacetylenic Ketones into Benzimidazoles

“…A possible transformation of D′ also includes reversible pyrrolo[1,2‐ c ]imidazole system J formation by intramolecular pyrrolyl anion attack to benzimidazolyl carbon through TS D′–J . Similar [3+2]‐cycloaddition of acylpyrrolylacetylenes to the C=N bond in 1‐pyrrolines was recently observed [22] . But in this case the magnitude of TS D′–J barrier is lower compared with that of TS D′–E .…”

“…Similar [3 + 2]cycloaddition of acylpyrrolylacetylenes to the C=N bond in 1pyrrolines was recently observed. [22] But in this case the magnitude of TS D'-J barrier is lower compared with that of…”

Acylmethylidenepyrrolo[1,2-c]oxazoles via [3+2]-cyclization of 2-acylethynylpyrroles with carbonyl compounds

“…17 Second, these compounds proved to be efficient building blocks for a variety of pyrrole heterocyclic ensembles. 18 Third, such cyclization may open a route to hitherto unknown pyrrolo[1,2- c ]oxazoles free of exocyclic carbonyl groups and functionalized by acylmethylidene substituents, which promise rich chemical modifications.…”