An Unprecedented Retro-Mumm Rearrangement Revealed by ESI-MS/MS, IRMPD Spectroscopy, and DFT Calculations

Claudio Iacobucci; Samantha Reale; Massimiliano Aschi; Jos Oomens; Giel Berden; Francesco De Angelis

doi:10.1002/chem.201800347

An Unprecedented Retro-Mumm Rearrangement Revealed by ESI-MS/MS, IRMPD Spectroscopy, and DFT Calculations

Chemistry. 2018 May 11;24(27):7026-7032. doi: 10.1002/chem.201800347. Epub 2018 Apr 26.

Authors

Claudio Iacobucci^{1

2}, Samantha Reale², Massimiliano Aschi², Jos Oomens³, Giel Berden³, Francesco De Angelis²

Affiliations

¹ Current address: Institute of Pharmacy, Martin Luther University Halle-Wittenberg, Wolfgang-Langenbeck-Strasse 4, 06120, Halle (Saale), Germany.
² Dipartimento di Scienze Fisiche e Chimiche, Università degli Studi dell'Aquila, Via Vetoio, Coppito, 67100, L'Aquila, Italy.
³ Radboud University Nijmegen, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, 6525 ED, Nijmegen, The Netherlands.

PMID: 29517821
DOI: 10.1002/chem.201800347

Abstract

Brønsted acids and protic solvents mediate acyl transfer, known as the Mumm rearrangement, from imidates to the corresponding acylamides. This represents a key step in several reactions, for example, the Ugi four-component reaction (U-4CR) and Passerini three-component reaction (P-3CR). Herein, an unprecedented break of the non-reversibility of the Mumm rearrangement is reported. A combination of electrospray tandem mass spectrometry (ESI-MS/MS), infrared multiphoton dissociation (IRMPD) ion spectroscopy and theoretical calculations demonstrates the occurrence of the retro-Mumm rearrangement of protonated isopeptides in the gas phase. In the gas phase, the extra proton acquired during ESI promotes the backward isomerisation reaction in a catalytic fashion.

Keywords: acyl transfer; gas-phase reactions; laser spectroscopy; multicomponent reactions; reaction mechanisms.