R = Me, Ar = Ph R = Me, Ar = 4-CIC6H4 R = Me, Ar = 4-MeC6H4

Scheme 26 Manganese(III)-catalyzed aerobic oxidation of 3-substituted 4-hydroxy-1H-quinolin-2-ones in the presence of 1,1-diarylethenes

In order to find other products, the rest of the residue was scrutinized, and the quite unique [4.4.3]propellane-type cyclic peroxides were isolated (Scheme 25). The peroxy O - O bond length (1.464 A) was analogous to that of the reported crystalline 1,2-dioxanes (normally 1.44-1.47 A) [77,128,133]. Although the use of the N-nonprotected quinolinones (R = H) resulted in a complex mixture, only the [4.4.3]propellane-type cyclic peroxides were isolated (Scheme 25).

Since it was found that the a-carbon of the amide carbonyl in the 4-hydroxy-1ff-quinolin-2-ones was very easily oxidized by manganese(III) to form double hydroperoxyalkylated quinolinediones, even when an excess amount of the quinolinones were employed under very mild aerobic oxidation conditions, the 3-substituted quinolinones were prepared. Aerobic oxidation with alkenes was investigated in an effort to prevent the double hy-droperoxyalkylation from taking place and to produce the cyclic peroxide. This process was successful and the corresponding quinoline-fused endoperoxides were obtained in good yields (Scheme 26). However, the quinolinones substituted by a bulky group rather than by the methyl group preferentially gave the corresponding acyclic monohydroperoxides [150].

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