Elsevier

Tetrahedron Letters

Volume 46, Issue 45, 7 November 2005, Pages 7761-7764
Tetrahedron Letters

Aza-Michael reactions catalyzed by samarium diiodide

https://doi.org/10.1016/j.tetlet.2005.09.039Get rights and content

Abstract

Samarium diiodide catalyzes the Michael addition of aromatic amines onto α,β-unsaturated N-acyloxazolidinones to form β-aminoacid derivatives. Aza-Michael reactions can be followed by an amidation reaction with the aromatic amine, leading to β-aminoamides. β-Amino-N-acyloxazolidinones are selectively obtained with o-anisidine, while amidation reaction is observed with p-anisidine.

Graphical abstract

Samarium diiodide catalyzes the Michael addition of aromatic amines onto α,β-unsaturated N-acyloxazolidinones to afford β-amino-N-acyloxazolidinone or β-aminoamide or a mixture of both products depending on the reaction conditions.

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Introduction

The development of catalysts for the formation of carbon–nitrogen bonds by simple addition of amines to double bonds is a focus of increasing interest.1 The few examples of catalyzed reactions involving aliphatic olefins are realized using high pressures and high temperatures.2 Palladium-catalyzed addition of amines to 2,3-dihydrofuran or 3,4-dihydro-2H-pyran forms α-aminotetrahydrofurans and α-aminopyrans,3 while cationic Pd diphosphine complexes catalyze the addition of amines on styrene as well as on α,β-unsaturated esters.4 The aza-Michael reaction, that is, addition of nitrogen nucleophiles on activated double bonds, is of synthetic interest since it provides an easy route to β-aminoacid derivatives.5 This latter reaction is catalyzed by Lewis acids such as silica,6 transition metal and lanthanide chlorides,7 or triflates.8 Recently, several types of transition metals have been found by high-throughput method to catalyze the addition of amines to acrylic acid derivatives.9 Diastereoselective or enantioselective catalytic aza-Michael reactions have been reported,10 although reactions involving amines have been scarcely investigated.11

We have previously studied the scope of the reactivity of samarium diiodide as a Lewis acid type catalyst. We have reported SmI2(THF)2 in methylene chloride to be an efficient precatalyst for carbon–carbon bond forming reactions, such as aldol, Michael, Diels–Alder, or tandem Michael-aldol reactions.12 Samarium diiodide is also an active catalyst for carbon–nitrogen bond forming reactions, such as the ring opening of epoxides by amines, to give β-aminoalcohols.13 In this letter, we present our results concerning samarium diiodide-catalyzed aza-Michael additions of amines to α,β-unsaturated N-acyloxazolidinones.

Section snippets

Results

α,β-Unsaturated N-acyloxazolidinones have found numerous applications as chelating substrates in Lewis acid catalyzed reactions, especially for enantioselective catalysis.14 By the use of these substrates in Diels–Alder reactions catalyzed by lanthanide iodo binaphthoxides, we have carried out cycloadditions with moderate enantioselectivity.15 We then wished to investigate the reactivity of α,β-unsaturated N-acyloxazolidinones as Michael acceptors in samarium diiodide-catalyzed additions of

Conclusion

Samarium diiodide catalyzes the Michael addition of aromatic amines onto α,β-unsaturated N-acyloxazolidinones yielding β-aminoacid derivatives either as β-amino-N-acyloxazolidinones, or as β-amino amides, or as mixtures, depending on the nature of amine and on the amine/substrate ratio. This is explained by an amidation reaction of the aza-Michael product with the aromatic amine. Amidation reactions occurred with high rates in experiments involving aniline and p-anisidine. When excess of amine

Acknowledgements

We thank CNRS for financial support and MENRT for Iréna Reboule Ph.D. grant. We are indebted to Hélène Guerrand for technical assistance and to Professor Fiaud for fruitful discussions and preparation of this manuscript.

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