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An improved coupling procedure for the barton‐zard pyrrole synthesis
Author(s) -
Bobál Pavel,
Lightner David A.
Publication year - 2001
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570380239
Subject(s) - chemistry , potassium carbonate , pyrrole , solvolysis , halogenation , acetic acid , organic chemistry , base (topology) , hydrogen peroxide , potassium hydroxide , medicinal chemistry , combinatorial chemistry , hydrolysis , mathematical analysis , mathematics
An improved final step in the Barton‐Zard pyrrole synthesis uses inexpensive potassium carbonate as base in the coupling‐cyclization reaction of vic ‐nitro‐acetates with isocyanides. In this modification the isolated yields of synthetically useful 2‐carboalkoxypyrroles ( 1a,b and 3 ) and 2‐( p ‐toluenesulfonyl)pyrroles (2a,b) consistently rise to the 78‐89% range. Conversion of 2a to 5‐( p ‐toluenesulfonyl)‐2‐pyrrolinone 4 is conveniently and directly achieved by reaction with 30% hydrogen peroxide in acetic acid, thus circumventing the commonly used two step procedure involving bromination followed by solvolysis.