Effect of Substituents, Solvent, and Temperature on the Reactivity of the Zwitterionic Peroxides Arising from the Photo-Oxygenation of 2-(Methoxymethylidene)- and 2-(Phenoxymethylidene)adamantane

Article abstract of DOI:10.1002/hlca.19840670824

The photo-oxygenation of 2-(methoxymethylidene)adamantane (3) creates a zwitterionic peroxide which may be captured by acetaldehyde to give the corresponding pair of diastereoisomeric tricyclo<3.3.1.1^3,7>decane-2-spiro-6'-(3'-methyl-5'-methoxy-1',2',4'-trioxanes) (4).Ease of capture depends strongly on solvent polarity and temperature.When these are low, yields of trioxane are high (ca. 80percent).Conversely, 1,2-dioxetane formation is favoured at high temperature and solvent polarity. 2-(Phenoxymethylidene)adamantane (5), on photo-oxygenation, only gives the corresponding 1,2-dioxetane, even in the presence of acetaldehyde.From a Hammett study of the photo-oxygenation of the enol ether 5 and its p-methoxy, p-methyl, p-chloro, and m-chloro derivatives (9, 11, 13, and 15), a good linear relation was found between substituent constants and oxygenation rates which yielded reaction constants (ρ) of -2.59, -2.40, -1.09, and -0.90 in benzene, AcOEt, CH2Cl2, and MeOH, respectively.This data attests to the formation of a zwitterionic peroxide which enjoys stabilization from its own substituents and by competing solvation and further explains the predominance of dioxetane to the detriment of trioxane formation.