Formation of Radical from Photoinduced Electron Transfer Reaction and its Application for Organic Synthesis

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In this research project, we found the following regio-and stereo-selective synthesis using radical species produced by photoinduced single electron transfer (SET) reactions.1. Irradiation of a CH_3CN solution of a-diketones and allylsilane/allylstannane-bifunctional reagent which possesses both allylic silane and allylic stannane functionality in the same molecule sharing the same carbon-carbon double bond afforded α-ketohomoallyl alcohol having allylsilane moiety in good yields. These results indicate that the (alkyl) C-Sn bond rather than (alkyl) C-Si bond of the cation radial formed by photoinduced SET reaction of the bifunctional reagent cleavages selectively to give allylic radical having allylsilane moiety, and the resulting allylic radical couples with semidione radical to form the α-ketohomoallyl alcohol. When the treatment of the irradiated mixture with Mg(CO_4)_2 cis-methylenecyclopentane-1, 2-diols were obtained, whereas the treatment with tetrabutylammonium fluoride (TBAF) yielded trans-1, 2-diols.2. 1, 2-Naphthoquinone reacted with γ-substituted allyltin reagents in both thermal and photochemical conditions to yield 4-allyl-1, 2-naphthoquinone. The opposite regioselectivity of introduced allylic moiety was observed in both reaction conditions.3. The photochemical reaction of 1, 2-naphthoquinones with allylsilanes afforded [3+2] cycloadducts via diradical intermediate, which was converted to 3-allyl-1, 2-naphthoquinones in moderate to good overall yields by treatment with boron trifluoride, ammonium cerium nitrate or TBAF.