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A New Access to 2‐(Alkylamino)‐ and 2‐(Arylamino)pyrroles by Addition of Isocyanides to Protonated 1‐Azabutadienes
Author(s) -
Marchand Evelyne,
Morel Georges,
Sinbandhit Sourisak
Publication year - 1999
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/(sici)1099-0690(199907)1999:7<1729::aid-ejoc1729>3.0.co;2-s
Subject(s) - chemistry , isocyanide , protonation , deprotonation , chloroform , acetonitrile , pyrrole , medicinal chemistry , autoxidation , photochemistry , ring (chemistry) , organic chemistry , ion
A number of 5‐(alkylamino)‐ or 5‐(arylamino)‐2 H ‐pyrrolium salts 3 or 5 have been obtained by treating the 1‐aza‐1,3‐diene hydrochlorides 2 with isocyanides R 4 NC in refluxing acetonitrile or chloroform for a few hours. Depending on the experimental conditions, deprotonation of these species can occur in the reaction medium to furnish the corresponding 2‐aminopyrroles 4 and 6 . Insertion of isocyanide into a carbon–hydrogen bond of the pyrrolium salts can also lead to the generation of the (pyrrol‐2‐yl)methyleneiminium chlorides 7 – 9 . Under similar conditions, treatment with an excess of tert ‐butyl isocyanide converts the protonated α‐chlorocinnamaldimines 2j , k into the 5‐( tert ‐butylamino)pyrrole‐2‐carbonitriles 13 . Structural assignments of all the cycloadducts have been made on the basis of their NMR‐spectroscopic properties, particularly the effects observed in NOEDIFF experiments. Mechanisms are suggested to account for the ring‐closure reactions and autoxidation of pyrroles 4 and 6 under atmospheric oxygen to give the 5‐imino‐2‐pyrrolinones 17 and 18 .