Fused indolones

Other ring contractions that give azapentalene derivatives include the rearrangement of a fused oxazine to a pyrazolo[l,5-a]indol-4-one with acetic anhydride,165 and an interesting photochemical contraction of a cyclic lactone, which produces an isomeric fused indolone by a mechanism thought to involve the first meta photo-Fries rearrangement [Eq. (19)].166 The product was used as an intermediate for the synthesis of mitomycin antibiotics (Section VI,A). 

Indolones and isoindolones have been utilised in the synthesis of fused azepine derivatives. In the one reaction, rearrangement of the alkynes 18 to 2-benzazepine-l,5-diones 19 in the presence of Lewis acids has been reported <96XL393>. Xhe yields vary from moderate to very good. Xricyclic azepines 20 are obtained by the reaction of the 4-[2 -(p-toluenesulfonyloxy)ethyl]-2-oxindole with imines <96JHC209>. 

We have studied the reaction of similar cyclic -substituted enaminones which yielded indolones when the reaction was carried out in acetic acid and the quinones had lower oxidation potential, thus preventing prior oxidation of the enaminones. Secondary aminomethylene derivatives of cyclopentanone, cyclohexanone and cycloheptanone reacted with the quinones to presumably form intermediate spiro compounds, as a consequence of normal enaminone chemistry. However, this was unexpectedly followed by rearrangement with ring expansion to indolones (equation 158). In this way carba-zoles, cycloheptindoles and cyclooctindoles can be obtained by a simple entry to this class of indoles, although partially in low yields222-224. Due to their bifunction-ality the produced indol-2-ones are versatile synthons for fused heterocycles (e.g. triazepino- and pyrazino-carbazoles) which become easily accessible225,226. 

Haider N, Kaferbock J et al (1999) Diels-Alder reaction of pyrano[3,4-b]indolones with an electron-deficient pyridazinone a new pathway to carbazole-fused pyridazines. Heterocycles 51 2703-2710... 

When applied to olefinic anilines, this type of process leads to fused lactams. While o-vinyl anilines selectively yield indolones (Scheme 55), o-allyl anilines afford complex mixtures of five-, six-, and seven-membered rings. 

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