Photoinduced molecular transformations. 128. Regioselective [2 + 2] photocycloaddition of 3-acetoxyquinolin-2(1H)-one with alkenes and formation of furo[2,3-c]quinolin-4(5H)-ones, 1-benzazocine-2,3-diones, and cyclopropa[d]benz[1]azepine-2,3-diones via a .beta.-scission of cyclobutanoxyl radicals generated from the resulting [2 + 2] photoadducts
作者:Kazuhiro Kobayashi、Masayoshi Suzuki、Hiroshi Suginome
DOI:10.1021/jo00028a037
日期:1992.1
We have found that [2 + 2]pi photoadducts can be obtained by the photoaddition of 3-acetoxyquinolin-2(1H)-one with acyclic and cyclic alkenes. The photoaddition of 3-acetoxy-2-quinolin-2(1H)-one with 2-methylpropene, 2,3-dimethyl-2-butene, and 2-methoxypropene thus afforded regioselective head-to-tail adducts in 59-97% yields. The photoaddition of 3-acetoxy-2-quinolin-2(1H)-one with cyclopentene and cyclohexene resulted in the formation of sterically disfavored cis-cisoid-cis photoadducts as the major products, with the accompanying formation of cis-transoid-cis photoadducts as the minor products in combined yields of 87 and 66%, respectively. The photolysis of the hypoiodites generated in situ from cyclobutanols derived from all of the photoadducts induced beta-scissions at the outer bonds of the corresponding cyclobutanoxyl radicals to give furo[2,3-c]quinolin-4(5H)-ones in 15-50% yields with an accompanying formation of 7- and 8-membered lactams arising from beta-scissions at the catacondensed bonds of the cyclobutanoxyl radicals in 2-62% yields. The molecular structure of one of the novel 7-membered lactams that successively fused with cyclopropane and cyclopentane rings was established to be trans-5,8,9,10,10a,10b-hexahydro-5-methylcyclopenta[3,4]cyclopropa[1,2-d]benzazepine-6,7-dione by X-ray crystallographic analysis. The pathways leading to the formation of all of these products arising from beta-scissions are discussed.