PHOTOINDUCED MOLECULAR-TRANSFORMATIONS .110. FORMATION OF FUROQUINOLINONES VIA BETA-SCISSION OF CYCLOBUTANOXYL RADICALS GENERATED FROM [2+2] PHOTOADDUCTS OF 4-HYDROXY-2-QUINOLONE AND ACYCLIC AND CYCLIC ALKENES - X-RAY CRYSTAL-STRUCTURE OF (6A-ALPHA,6B-BETA,10A-BETA,10B-ALPHA)-(+/-)-10B-ACETOXY-6A,6B,7,8,9,10,10A,10B-OCTAHYDRO-5-METHYLBENZO[3,4]CYCLOBUTA[1,2-C]QUINOLIN-6(5H)-ONE

Several [2 + 2] photocycloadducts were prepared by the photoaddition of 4-acetoxy-2-quinolone or 4-hydroxy-iV-methyl-2-quinolone with cyclic and acyclic olefins. The photoaddition of 4-acetoxy-2-quinolone with cyclopentene gave, exclusively, cis-cisoid-cis adduct while that with 1-methoxycyclopentene gave, exclusively, a head-to-head cis-transoid-cis adduct. Photoaddition with cyclohexene, on the other hand, afforded cis-cisoid-cis together with cis-transoid-cis adducts. The molecular structure of the latter was determined by an X-ray crystallographic analysis of its N-methyl derivative. Photoadditions of 4-acetoxy-2-quinolone and 4-hydroxy-iV-methyl-2-quinolone with ethyl vinyl ether, 2-methoxypropene, isopropenyl acetate, and vinyl benzoate were all regioselective, each giving the corresponding single or double stereoisomers of head-to-head adduct(s). The photolysis of the hypoiodites generated from cyclobutanols derived from the photocycloadducts between 4-acetoxy-2-quinolone and cyclopentene or 2,3-dimethylbut-2-ene induced regioselective rearrangements of the corresponding alkoxyl radicals to give 2,3-furo-4-quinolinones. In contrast, 3,4-furo-2-quinolinones are regioselectively formed when the hypoiodites generated from cyclobutanols derived from the photoadducts of 4-acetoxy-2-quinolone with vinyl ethyl ether, isopropenyl acetate, or 1-methoxycyclopentene in benzene are irradiated. Both 3,4-furo-2-quinolinone and 2,3-furo-4-quinolinone are formed when the hypoiodites of cyclobutanols derived from the photoadducts between 4-hydroxy-2-quinolone and vinyl esters in benzene are irradiated. The pathways leading to the 2,3-furo-4-quinolinones and 3,4-furo-2-quinolinones as well as the selectivityin the formation of the two isomeric furoquinolinones from the cyclobutanoxyl radicals are discussed. © 1990, American Chemical Society. All rights reserved.