Electronic effects in the regioselectivity of the singlet oxygen and 4-methyl-1,2,4-triazoline-3,5-dione ene reactions with isobutenylarenes

The regioselectivity of the ene pathway in the photooxidation of several 1-aryl-2-methylpropenes, as probed by stereoselective deuterium-labeling, depends on the electronic nature of the para phenyl-substituents. The reaction of the same array of alkenylarenes with 4-methyl-1,2,4-triazoline-3,5-dione (MTAD) gives ene products with an impressive >97% allylic hydrogen abstraction from the more substituted side of the alkene.