O-Benzenedisulfonimide as a Reusable Brønsted Acid Catalyst for Hetero-Michael Reactions

Abstract

The hetero-Michael reactions among various oxygen, sulfur, and nitrogen nucleophiles and α,β-unsaturated compounds were carried out in the presence of catalytic amounts of o-benzenedisulfonimide as Brønsted acid organocatalyst. The reaction conditions were very mild, and the yields of target products were good. The catalyst was easily recovered and purified, ready to be used in further reactions. This ability grants economic and ecological advantages.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.

GRAPHICAL ABSTRACT

Keywords:

• Brønsted acid
• conjugate addition
• homogeneous catalysis
• Michael reaction
• recyclable catalyst

ACKNOWLEDGMENT

This work was supported by the University of Torino.

Notes

^a Yields refer to the pure products.

^b After 24 h, unreacted 2a and 5 were detected by GC and GC-MS. Nevertheless, the reaction was stopped and the crude residue, purified in a silica-gel chromatography column (eluent: PE/Et₂O 9.8:0.2), afforded pure 10a.

^c On the GC, GC-MS, and NMR analyses, the crude residue was the virtually pure 10a.

^d After 24 h, unreacted 2a and 5 were detected by GC and GC-MS. Only weak traces of 10a were detected.

^a Yields refer to the pure products.

^b The reaction was performed with 5 mmol of 2a and 5 and 5 mol% of 1 (55 mg, 0.25 mmol).

^c Recovered 1 was used as a catalyst in entry 2.

^d Recovered 1 was used as catalyst in entry 3.

^e Recovered 1 was used as a catalyst in entry 4.

^f Recovered 1 was used as a catalyst in entry 5.

^g Recovered 1 was used as catalyst in entry 6.

^a All the reactions were performed with 5 mol% of 1; the reactants are in equimolar amounts (5 mmol).

^b Yields refer to the pure and isolated products.

^c On the GC, GC-MS, and NMR analyses, the crude residues were the virtually pure hetero-Michael adducts 10 and 11.

^d The crude residue was purified in a silica-gel chromatography column (eluent: PE/Et₂O 9.8:0.2).

^a All the reactions were performed with 5 mol% of 1; the reactants are in equimolar amounts (5 mmol).

^b Yields refer to the pure and isolated products.

^c On the GC, GC-MS, and NMR analyses, the crude residues were the virtually pure hetero-Michael adducts 10 and 11.

^a All the reactions were performed with 5 mol% of 1; the reactants are in equimolar amounts (5 mmol).

^b Yields refer to the pure and isolated products.

^c On the GC and GC-MS analyses of the crude residue, three products were detected: 12a, 13a, and 14a. However, it was impossible to separate them by chromatography column.

^d On the GC and GC-MS analyses of the crude residues, weak traces of compounds 13 and 14 were detected. The crude residues, purified in a silica-gel chromatography column (eluent: PE/Et₂O 9.8:0.2), afforded pure compounds 12.

^e The crude residues were purified in a silica-gel chromatography column (eluent: PE/Et₂O 9.8:0.2). For more details see also the Supplementary Material.

^a All the reactions were performed with 5 mol% of 1; the reactants are in equimolar amounts (5 mmol).

^b Yields refer to the pure and isolated products.

^c On the GC, GC-MS, and NMR analyses, the crude residues were the virtually pure hetero-Michael adducts 12.

^d The crude residues were purified in a silica-gel chromatography column; eluent: PE-Et₂O (9.8:0.2).

^e The reaction was performed without catalyst 1.

^f On the GC and GC-MS analyses of the crude residue, two products were detected: 12h and N,N-bis(2-ethoxycarbonylethyl)benzylamine. However, it was impossible to separate them by chromatography column.

^g The reaction was performed using the benzylammonium salt 16 as catalyst (5 mol%; 81.5 mg).

^h On the GC and GC-MS analyses of the crude residue two products were detected: N-benzylideneaniline (15c) and N-(1-phenyl-2-nitroethyl)aniline. However, it was impossible to separate them by chromatography column. For more details see also the Supplementary Material.