Abstract
The photochemical reactions of some 2-alkyl-l, 3-dioxolanes and 2-alkyl-l, 3-oxathiolanes in CFC13 in the presence of benzophenone yield exclusively the open 2-chloroethyl carboxylic esters and S-2-chloroethyl thio-carboxylic esters respectively. Photochemically excited benzophenone abstracts the hydrogen atom at carbon between the heteroatoms from the substrate to give intermediate cyclic (thio)acetal radicals which can be trapped efficiently by 2-nitroso-2-methylpropane in inert solvents. The resulting nitroxides are identified by their ESR hfs constants. No ring-opened (thio)ester radicals could be trapped. The course of photolysis of optically active 2RS, 4R-(—)-2-methyl-4-phenyl-1, 3-dioxolane and other (racemic) 2, 4-disubstituted-l, 3-dioxolanes supports a mechanism in which a cyclic radical abstracts halogen from the solvent to form an intermediate cyclic chloro-(thio)acetal. Heterolytic cleavage of the new C-Cl bond gives the well stabilized cyclic carbonium ion and chloride anion. Nucleo-philic attack of chloride ion at the C-4 or C-5 carbon atom (involving inversion for a chiral C-4) leads to ring rupture and formation of the final product.
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© 1971 Martinus Nijhoff, The Hague, Netherlands
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Hartgerink, J.W. (1971). Photochemically Initiated Reactions of Substituted 1,3-Dioxolanes and 1, 3-Oxathiolanes in CFCI3 . In: Spin Trapping by Nitrosoalkanes. Springer, Dordrecht. https://doi.org/10.1007/978-94-011-9441-9_4
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DOI: https://doi.org/10.1007/978-94-011-9441-9_4
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