Synthesis of spiro[2H‐indole‐2,1′‐1H‐isoindole]‐3,3′‐diones, spiro[1H‐isobenzofuran‐1,2′‐2H‐indole]‐3,3′‐diones and spiro[benzofuran‐2,1′‐isobenzofuran]‐3,3′‐diones via transannular reactions of eight membered ring intermediates

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Abstract
An auto oxidation‐rearrangement product 4 was isolated from a high dilution reaction of ninhydrin with 3,4,5‐trimethoxyaniline in water. A general synthesis of this compound and its derivatives 4–6 was devised by oxidation of tetrahydroindeno[1,2‐b]indol‐10‐ones 1–3 with sodium periodate to give isoindolo[2,1‐a]‐indole‐6,11‐diones 4–6 in good yield. Compounds 4–6 can be easily transformed into spiro[1H‐isobenzofuran‐1,2′‐2H‐indole]‐3,3′‐diones 8–10, spiro[2H‐indole‐2,1′‐1H‐isoindole]‐3,3′‐diones 11–13 and isoindole[1,2‐a:2′,1′‐b]pyrimidine‐5,15‐diones 15, 16 in high yields. Analogous reactions were performed on 3‐amino‐5a, 10a‐dihydroxybenzo[b]indeno[2,1‐d]furan‐10‐one (17) to give a dibenzoxocintrione 18, spiro‐[benzofuran‐2,1′‐isobenzofuran]‐3,3′‐dione 19 and an isoindol‐1‐one 20.

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