Efficient dehydrogenation of 1,2,3,4-tetrahydroquinolines mediated by dialkyl azodicarboxylates

ABSTRACT

Various dialkyl azodicarboxylates were investigated for the dehydrogenation of 1,2,3,4-tetrahydroquinolines to quinolines. The dehydrogenation rates varied according to the electronic and steric nature of the used dialkyl azodicarboxylates. Among solvents screened with diethyl azodicarboxylate, chloroform exhibited superior results to others. A variety of 1,2,3,4-tetrahydroquinolines underwent the present dehydrogenation to produce the corresponding quinolines. Diethyl hydrazodicarboxylate, which is a reduced species of diethyl azodicarboxylate, was easily separated for recycle.

GRAPHICAL ABSTRACT

KEYWORDS:

• Dehydrogenation
• diethyl azodicarboxylate
• organic synthesis
• quinolines
• 1,2,3,4-tetrahydroquinolines

Notes

¹Instead of CHCl₃, the use of other solvents such as CH₃CN and dichloroethane (DCE) at 70 °C also gave high product yields. For example, the yields of 2i were 97% in CH₃CN and 96% in DCE at 70 °C.

Additional information

Funding

This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (NRF-2015R1C1A1A02037185).