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

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[e]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.