On the reactions of 1,3-isoquinolinediones with singlet oxygen

• Published in: Tetrahedron 1999-07, Vol.55 (30), p.9185-9204
• Main Authors: Ling, Ke-Qing, Ye, Jia-Hai, Chen, Xian-Yang, Ma, De-Jian, Xu, Jian-Hua
• Format: Article
• Language: English
• Subjects: 3-isoquinolinediones; [4+2] cycloaddition; enolization; photooxygenation; Schenck ene reaction; singlet oxygen
• ISSN: 0040-4020; 1464-5416
• DOI: 10.1016/S0040-4020(99)00502-5

Reactions of 1,3-isoquinolinediones 5 and 4-alkylated 1,3-isoquinolinediones 13 with singlet oxygen are entirely dominated by their enolization and proceed smoothly in benzene in the presence of pyridine as a base and a hydrogen bond acceptor. The products are triketones 6 and benzoisofuranones 7 for 5, and hydroperoxides 14, hydroxides 15 and benzoisofuranones 16 for 13. It was found that hydrolysis of 6 afforded the isoindolones 8 and not products 7, whereas alkaline cleavage of the hydroperoxide 14a yielded not only 16a, but also the isoindolone 19a. In view of these observations, an unusual [4+2] cycloaddition of the electron-rich enol 21 with singlet oxygen is proposed to be responsible for the formation of products 7 and 16, while products 6, 14 and 15 arise from both the [4+2] cycloaddition and the usual Schenck ene reaction pathways. This special diene reactivity of the isoquinolinone system towards singlet oxygen is further interpreted by frontier molecular orbital (FMO) interaction considerations. Reactions of 1,3-isoquinolinediones such as 5 with singlet oxygen ( 1O 2) mediated by the enol form 21 and proceeding via [4+2] cycloaddition and Schenck ene reaction mechanisms are described.