✍ Scribed by Heiner Graalfs; Roland Fröhlich; Christian Wolff; Jochen Mattay
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Intermolecular addition of radicals to the 1,3-dioxin-4-ones an unsaturated side chain were attacked by radicals at the terminal double bond. In the case of irradiation of 32b in 1,3-1a,b and 2a,b with (-)-menthone incorporated as chiral auxiliary in 2-position were investigated. Photochemically dioxolane a cyclization followed the intermolecular addition of a 1,3-dioxolan-2-yl radical and the dispiro compound 36 generated radicals from 1,3-dioxolane, oxolane, and 2propanol were added with high facial selectivity from the was formed. However, the formation of dispiro compound 40 required two reaction steps starting with irradiation of 32b more exposed a-side. Intramolecular addition of 1,3dioxolan-2-yl radicals to chiral dioxinones proceeded less and bromotrichloromethane. The achiral 1,3-dioxin-4-one 44 possessing an unsaturated side chain at C-2 was attacked by efficiently and with lower selectivity also from the a-side. Nevertheless, it was possible to form the new spirocyclic 1,3-dioxolan-2-yl radicals preferentially at C-6. compounds 22-27. The 1,3-dioxin-4-ones 32a,b possessing New address: Merck KGaA, Darmstadt, Germany. route for the formation of CϪC bonds. [11] However, only
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