Photooxidation of 2-(tert-Butyl)-3-Methyl-2,3,5,6,7,8-Hexahydroquinazolin-4(1H)-one, an Example of Singlet Oxygen ene Reaction.

Singlet oxygen ene reactions produce 2-(tert-butyl)-4a-hydroperoxy-3-methyl-2,4a, 5,6,7,8-hexahydroquinazolin-4(3H)-one quantitatively during diffusion crystallization of 2-(tert-butyl)-3-methyl-2,3,5,6,7,8-hexahydroquinazolin-4(1H)-one in n-hexane/CH2Cl2 solvent mixture. To confirm this photo-oxidation, a 1H-NMR study in CDCl3 was performed with exposure to ambient conditions (light and oxygen), with neither additional reactants nor catalysts. A theoretical study at the B3LyP/6311++G** level using the QST2 method of locating transition states suggests a two-step mechanism where the intermediate, which unexpectedly did not come from the peroxide intermediate, has a low activation energy.