Cobalt(II)-Catalyzed Proficient Synthesis of Enaminones from Aryl Alkenes and Amines

Subham Sau; Krishna Mohan Das; Swapnamoy Ghosh; Arunabha Thakur

doi:10.1055/a-2377-0230

Synlett, Table of Contents

Synlett 2024; 35(20): 2403-2408
DOI: 10.1055/a-2377-0230

letter

Special Issue to Celebrate the 75th Birthday of Prof. B. C. Ranu

Cobalt(II)-Catalyzed Proficient Synthesis of Enaminones from Aryl Alkenes and Amines

Authors

Subham Sau‡
Krishna Mohan Das‡
Swapnamoy Ghosh
Arunabha Thakur∗

Abstract

All articles of this category

Dedicated to Professor B. C. Ranu on his 75th birthday.

Abstract

A simple, cost-effective, and modular strategy has been developed to synthesize synthetically and pharmaceutically active enaminones by oxidative amination of aryl alkenes with amines and CHCl₃, using tert-butyl hydroperoxide as an oxidant. We describe the synthesis of enaminones from vinyl arenes and sterically hindered N,N-diisopropylethylamine (DIPEA) by employing an Earth-abundant cobalt salt as a catalyst within a very short reaction period for the first time. Furthermore, nitrogen- and oxygen-containing heterocyclic compounds have been synthesized from these highly functionalized enaminones. Moreover, various control experiments, such as radical trapping reaction, along with a Hammett analysis with various types of substituents on the styrene ring unraveled the detailed mechanism of this reaction pathway.

Key words

enaminones - vinylarenes - cobalt catalysis - Hammet analysis - Oxidative amination

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References

References and Notes

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18 Enaminones 4a–q; General Procedure An oven-dried round-bottomed flask equipped with a stirrer bar was charged with CoCl₂·6H₂O (0.1 equiv, 0.1 mmol, 23.8 mg), DIPEA (3 equiv, 3 mmol, 0.52 mL), TBHP (3 equiv, 3 mmol, 0.29 mL), and toluene (1 mL). CHCl₃ (3 equiv, 3 mmol, 0.24 mL) was added to the mixture, followed by the appropriate styrene derivative 1 (1.0 equiv, 1.0 mmol). The mixture was stirred for 3 h in a preheated oil bath at 60 °C, then cooled to r.t. H₂O was added, and the mixture and extracted with CH₂Cl₂ (3 × 10 mL) and H₂O. The organic phase was washed with brine, dried (Na₂SO₄), and concentrated under reduced pressure. The crude product was purified by column chromatography [silica gel (100–200 mesh), EtOAc–PE (3:7 to 4:6)].
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Supplementary Material

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