Tetrahedron p. 3439 - 3456 (1990)
Update date:2022-09-26
Topics:
Chiu, Pak-Han
Sammes, Michael P.
3H-Pyrrole-3-carboxylic esters (4) have been prepared, in some cases together with isomers (5) and (6) having exocyclic double bonds, by cyclization of suitably substituted 2-ethoxycarbonyl-1,4-diketones (1) with liquid ammonia, followed by dehydration of the isolable 2-hydroxy-3,4-dihydro-2H-pyrrole intermediates (2) and (3) with aluminia in boiling solvents.Prolonged heating in toluene or p-xylene converts the 3H-pyrroles (4) quantitatively into isomeric 4-esters (11) and N-esters (13) of 1H-pyrroles via competitive <1,5>sigmatropic rearrangements.Isolable intermediate 2H-pyrrole-2-carboxylic esters (12) are converted similarly into the same products, under the same conditions.Detection of 3H-pyrroles (4) as intermediates in the latter reaction demonstrates for the first time the reversibility of the thermal 2H-pyrrole to 3H-pyrrole interconversion.
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Doi:10.1039/c39900000720
(1990)Doi:10.1039/d0sc04244g
(2020)Doi:10.1007/BF00765789
(1990)Doi:10.1039/c9ra04896k
(2019)Doi:10.1007/s11172-010-0366-y
(2010)Doi:10.1002/chem.201002871
(2011)