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 |
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Authors: | Charles W Jefford Hamish G Grant Danielle Jaggi John Boukouvalas Shigeo Kohmoto |
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Abstract: | 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 tricyclo3.3.1.13,7]decane-2-spiro-6′ -(3′ -methyl-5′ -methoxyl′, 2′, 4′ -trioxanes) ( 4 ). Ease of capture depends strongly on solvent polarity and temperature. When these are low, yields of trioxine are high (~ 80%). 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-dioxetene, even in the presence of acetaldehyde. From a Hammett, study of the-oxygenation of the enol ether 5 and 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 to the formation of a zwitterionic peroxide which enjoys stabilization from its won substituents and by competing solvation and further explains the predominance of dioxetane to the detriment of trioxane formation. |
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