LIGHT-INDUCED FREE-RADICAL REACTIONS OF 2-METHOXY-6-METHYLTETRAHYDROPYRAN: IRREVERSIBLE RING OPENING AND MULTISITE HYDROGEN ABSTRACTION

Article abstract of DOI:10.1021/jo00317a017

Acetophenone-initiated photodegradation of cis-2-methoxy-4-methyltetrahydropyran (7) in benzene solvent produced six products.The structures of the products, and studies using optically active 7, showed that hydrogen abstraction occurs at both C-2 and C-6 of the tetrahydropyran ring.The products derived from the C-2 radical indicated two pathways for this radical: ring opening and loss of methyl, which is consistent with previous work on other similar systems.Results with optically active 7 showed that the ring-opening pathway is irreversible.Generation of an open-chain radical independently also showed that cyclization to a six membered ring does not occur.The products from the photodegradation were trans-2-methoxy-6-methyltetrahydropyran (8), methyl hexanoate (10), 6-methyltetrahydropyran-2-one (9), methyl 5-phenylhexanoate (11), 1,7-dimethyl-7-phenyl-6,8-dioxobicyclo<3.2.1>octane (13), and 2-methoxy-2-(1-phenyl-1-hydroxyethyl)-6-methyltetrahydropyran (12).The yield of lactone 9 was found to be sensitive to the amount of residual oxygen present during the photolysis.