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

5 years ago

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

Maria Gdaniec, Paulina Wiśniewska, Łukasz Balewski, Zuzanna Drażba, Emilia Sieniawska, Justyna Rzewnicka, Joanna Fedorowicz, Jarosław Sączewski

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.

Publisher URL: http://dx.doi.org/10.1021/acs.joc.7b01851

DOI: 10.1021/acs.joc.7b01851