K. Moonen

Reductive imino-pinacol coupling reaction of halogenated aromatic imines and iminium ions catalyzed by precious metal catalysts using hydrogen

K.N.R. Dumoleijn, E. Van den Broeck, J. Stavinoha, V. Van Speybroeck, K. Moonen, C.V. Stevens

Journal of Catalysis

400, 103-113

2021

A1

Abstract

The first heterogeneously catalyzed process for the reductive coupling of imines and iminium ions is reported using precious metal catalysts in combination with hydrogen gas as the terminal reductant. The optimized method in terms of catalyst composition and reaction conditions allowed to produce aromatic vicinal diamines without the use of stoichiometric amounts of zero or low valent metals, which is currently the preferred method. The most important mechanistic features of the reaction were unraveled by a combined experimental and computational approach. The developed methodology is very efficient for the coupling of aromatic iminium ions with yields up to 88 % while imines give only low to moderate yields.

Gold Open Access

DOI

https://doi.org/10.1016/j.jcat.2021.05.023

Synthesis of Tricyclic Phosphonopyrrolidines via IMDAF: Experimental and Theoretical Investigation of the Observed Stereoselectivity

D.D. Claeys, K. Moonen, B.I. Roman, V.N. Nemykin, V.V. Zhdankin, M. Waroquier, V. Van Speybroeck, C.V. Stevens

Journal of Organic Chemistry

73 (20), 7921-7927

2008

A1

Abstract

During the synthesis of tricyclic phosphonopyrrolidines via intramolecular Diels−Alder reactions of 1-acylamino(furan-2-yl)methyl phosphonates, two isomers are formed in most cases. The presence of a short three-atom tether together with spectroscopic data, including difference NOE, revealed that the cycloaddition occurred exo, but the phosphonate substituent on the tether had an exo or endo orientation. This was confirmed via X-ray analysis. A thermodynamic preference for the product with the phosphonate function in the endo position was observed experimentally and was confirmed theoretically. Density functional theory methods and several high-level post Hartree−Fock procedures were used to rationalize the observed isomer ratio of the IMDAF-reactions. This was done for two different types of reagents: with the activating carbonyl group in the tether or as a substituent on the tether. For the first type of molecules there is a large steric hindrance of the bulky tether substituents that disfavors the exo-isomer. In the latter case, there was a very small energy difference between the transition states causing a mixture of epimers being formed.

DOI

http://dx.doi.org/10.1021/jo801138s

Unexpected Four-Membered over Six-Membered Ring Formation during the Synthesis of Azaheterocyclic Phosphonates: Experimental and Theoretical Evaluation

V. Van Speybroeck, K. Moonen, K. Hemelsoet, C.V. Stevens, M. Waroquier

JACS (Journal of the American Chemical Society)

128 (26), 8468-8478

2006

A1

Abstract

The cyclization of functionalized aminophosphonates is studied on both experimental and theoretical grounds. In a recently described route to phosphono-β-lactams [Stevens C. V.; Vekemans, W.; Moonen, K.; Rammeloo, T. Tetrahedron Lett. 2003, 44, 1619], it was found that starting from an ambident allylic anion only four-membered rings were formed without any trace of six-membered lactams. New anion trapping experiments revealed that the γ-anion is highly reactive in intermolecular reactions. Ab initio calculations predict higher reaction barriers for the γ-anion due to restricted rotation about the C−N bond and due to highly strained transition states during ring closure. The sodium or lithium counterion, explicit dimethyl ether solvent molecules, and bulk solvent effects were properly taken into account at various levels of theory.