The Elusive Paal–Knorr Intermediates in the Trofimov Synthesis of Pyrroles: Experimental and Theoretical Studies

We have used isoxazolo­[3,4-b]­pyridin-3­(1H)-one and isoxazolo­[3,4-b]­quinolin-3­(1H)-one as “masked” heterocyclic hydroxylamines to generate Paal–Knorr intermediates of the Trofimov pyrrole synthesis. The previously inaccessible intermediates, trapped by ethyl propiolate, were obtained by reactin...

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Published in:Journal of organic chemistry 2017-09, Vol.82 (18), p.9737-9743
Main Authors: Sączewski, Jarosław, Fedorowicz, Joanna, Gdaniec, Maria, Wiśniewska, Paulina, Sieniawska, Emilia, Drażba, Zuzanna, Rzewnicka, Justyna, Balewski, Łukasz
Format: Article
Language:English
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Summary:We have used isoxazolo­[3,4-b]­pyridin-3­(1H)-one and isoxazolo­[3,4-b]­quinolin-3­(1H)-one as “masked” heterocyclic hydroxylamines to generate Paal–Knorr intermediates of the Trofimov pyrrole synthesis. The previously inaccessible intermediates, trapped by ethyl propiolate, were obtained by reacting corresponding isoxazolones with 4-fold excess of ethyl propiolate under basic conditions at ambient temperature, and characterized by means of IR and NMR spectroscopic data as well as by single crystal X-ray analysis. Quantum chemical calculations of a [3,3]­sigmatropic rearrangement of the N,O-divinyl hydroxylamines to corresponding imino-aldehydes (Paal–Knorr intermediates) revealed that this reaction proceeds via chairlike transition state and is exothermic.
ISSN:0022-3263
1520-6904
DOI:10.1021/acs.joc.7b01851