Studies on the photochemical oxidation of N,N-diacyl-1,4-dihydropyrazine derivatives

ABSTRACT

The photochemical oxidation of N,N-diacyl-1,4-dihydropyrazines was investigated by irradiation from a medium-pressure mercury lamp. The main products of the photooxygenation were isolated and unambiguously confirmed by ¹H NMR spectra, ¹³C NMR spectra, H-H, C-H correlation spectra, high-resolution mass spectrometry, and single-crystal x-ray diffraction analysis. The complicated NMR spectra of main products were studied by variable-temperature NMR experiments. The mechanism of the photooxygenation of N,N-diacyl-1,4-dihydropyrazines is suggested to be a [2 + 2] cycloaddition of oxygen to the double bond.

GRAPHICAL ABSTRACT

KEYWORDS:

• [2 + 2] cycloaddition
• 1, 4-dihydropyrazines
• photooxygenation