Synthesis 2017; 49(15): 3453-3459
DOI: 10.1055/s-0036-1590839
paper
© Georg Thieme Verlag Stuttgart · New York

Superelectrophilicity in Michael-Type Reactions: Water Addition to 4-Nitrobenzodifuroxan

Sami Lakhdar*
a   Normandie Université, Laboratoire de Chimie Moléculaire et Thio-organique, CNRS-UMR 6507, ENSICAEN, Université de Caen Normandie, 6, Boulevard du Maréchal Juin, Caen 14000, France   Email: Sami.lakhdar@ensicaen.fr
,
b   Department Chemie, Ludwig-Maximilians-Universität München, Butenandtstrasse 5–13, Haus F, 81377 München, Germany   Email: Guillaume.berionni@cup.lmu.de
,
François Terrier*
c   Institut Lavoisier de Versailles, UMR CNRS 8180, Université de Versailles-St-Quentin, 45, Avenue des Etats-Unis, 78035 Cedex Versailles, France   Email: Terrier@chimie.uvsq.fr
› Author Affiliations
The authors are grateful to the CNRS and the University of Versailles for funding this research.
Further Information

Publication History

Received: 31 May 2017

Accepted after revision: 26 June 2017

Publication Date:
11 July 2017 (online)


Dedicated to Professor Herbert Mayr on the occasion of his 70th birthday

Abstract

Kinetic and thermodynamic measurements of the ease of covalent hydration of 4-nitrobenzodifuroxan (NBDF) to give the corresponding hydroxy adduct has been carried out over a large pH range of 0.82–12.23 in aqueous solution. A most important result is that water is the sole efficient nucleophile contributing to the hydration of this peculiar nitroolefin in the pH range 4–8. Based on this finding as well as a pK a H2O value of 2.85 for the complexation process there is no doubt that the electrophilic character of NBDF falls in the domain of superelectrophilicity defined with reference to covalent nucleophilic additions to 4,6-dinitrobenzofuroxan (DNBF; pK a H2O = 3.75) and related heterocycles. This also corresponds to a positioning of NBDF at the top of the electrophilicity scale E introduced by Mayr to describe the feasibility of nucleophilic-electrophilic combinations. Returning to the hydration of the series of activated olefins, it has been possible to expand the domain of reactivity of Michael acceptors by six orders of magnitude, going from benzylidenemalonitrile (pK a H2O = 10.70; E = –9.42) to the para-nitro-substituted benzylidene Meldrum’ s acid (pK a H2O = 3.46; E = –5.49). The positioning of these olefins on the pK a scale shows that not only 4-nitrobenzodifuroxan but also the unsubstituted Meldrum’s acid are located in the superelectrophilic region.