1,3-Dioxolane, photochemical addition

A general study of the photochemical addition of 2-propanol and 1,3-dioxolane to unsaturated sugars [48, 55, 56] shows the following order of reactivity (see Scheme 27) and yields mixtures of stereoisomers. 

Scheme 2.—Proposed Mechanism for Photochemically Initiated, Radical Addition of 1,3-Dioxolane to 5,6-Dideoxy-l,2-0-isopropylidene-a-D-xi//o-hex-5-enofuranose (3).

The photosensitized addition of 1,3-dioxolane and 1,3,5-trioxane to, alkenes was developed a number of years ago as a route to a-alkylated ethers (68JOC805). It has now been shown that 2-methyl-l,3-dioxolane will undergo a photochemically induced conjugate addition reaction to cyclohexenone to afford an adduct (327) in 54% yield which can be hydrolyzed to the diketone (328) (77CJC3986). Functionalized dioxolane (330) was also... 

The photosensitized 1-4 addition of alcohols to hexenopyranosuloses first reported by B. Fraser Reid and coworkers [58 a] has been developed with other studies on photoadditions of oxycarbinyl species such as polyols, acetals, dioxolanes, aldehydes. A mechanistic study on this photoaddition has been recently detailed [58 b] showing that the important photochemical event is hydrogen abstraction from methanol, for example, to form the hydroxymethyl radical. 

The epoxide is also formed from the reaction of C60 with dimethyldioxirane, and the 1,3-dioxolane (figure 9) is also obtained (Elemes et al. 1992). Photochemical irradiation of C60 in hexane had previously been shown to result in the addition of 2-5 oxygens, and also various methylene groups (the results depend upon the fullerene purity) (Wood et al. 1991). In this work, two oxygens were found to add to C70. 

Ghosh, A.K., Leshchenko, S., and Noetzel, M. (2004) Stereoselective photochemical 1,3-dioxolane addition to 5-alkoxymefhyl-2(5H)-furanone synthesis of bis-tetrahydrofuranyl ligand for HIV protease inhibitor UIC-94017 (TMC-114). Journal of Organic Chemistry, 69, 7822-7829. 

Scheme 3. Stereoselective photochemical 1,3-dioxolane addition route.

Although there exist numerous ground state reactions, photochemically induci asymmetric radical additions can be very efficient and even highly stereoselectr [125]. Furthermore, no particular functionalization of the starting material is n< essary prior to the formation of a C-C bond. In this context, the photosensiti addition of alcohols, cyclic acetals, and tertiary amines to electron-deficient kenes has been particularly studied. This will be illustrated by a few exampli First attempts to induce chirality in the photoinduced addition of ket radicals (e.g., U) involved a, 3-usaturated carbonyl compounds such as 208 rived from carbohydrates (Scheme 56) [126]. With benzophenone as sensitizi these radicals could be added stereoselectively, and similar reactions were carri out with dioxolane and a, 3-usaturated nitropyranones [127]. 

Irradiation of 1,3-dioxolanes in the presence of a sensitizer such as benzophenone (PhjCO), leads to the abstraction of an acetal hydrogen atom (by the triplet state ketone) to generate 1,3-dioxolanyl radicals, together with the resonance-stabilized diphenyl ketyl radical (Scheme 16). These nucleophilic 1,3-diox-olanyl radicals have been shown to add to a variety of alkenes to form adduct radicals, which can then accept a hydrogen atom from the diphenyl ketyl radical to give the desired alkylated product. The diastereoselective addition of 1,3-dioxolanyl radicals to alkenes bearing chiral auxiliaries has also recently been reported, while the photochemical alkylation of diketene with 2-undecyl-l,3-dioxolane has been utilized as a key step in the synthesis of (-)-tetrahydrolipstatin (Scheme 17). ... 

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