Dihydro-5,6-dihydroxyindoles 5,6-Dihydroxyindolines

The UV spectra of several derivatives 76 and 77 have been recorded and these are summarized in Table 4. 

Several studies have reported the chemical shifts of the ring protons in 5,6-dihydroxyindoline derivatives and these are tabulated in Table 5. 

The most significant 2,3-dihydro-5,6-dihydroxyindole is L-cyclodopa 78, also known as leucodopachrome, which is an intermediate in the biosynthesis of eumelanin and is formed by the spontaneous cyclization of dopaquinone 79 (92MI2) (04MI1). In turn, cyclodopa is readily oxidized to dopachrome 80 but this oxidation can be reversed chemically using sodium dithionite. Wyler and Chiovini have described the preparation of both enantiomers of cyclodopa using transformations 

Secondary catechol amines upon oxidation also cyclize to the 2,3-dihydroindoles which rapidly undergo further oxidation to the aminochrome. Typically, adrenaline gives adrenochrome 102 via leueoadrenochrome 101. Few examples of the intermediate indolines (e.g. 101) have been fully characterized. Work in this area 

The semiquinones of the 2,3-dihydro-5,6-dihydroxyindoles 124 (R = H, Et, R = H), generated by pulse radiolysis, were formd to decay via simple bimolecular disproportionation to the aminochromes 125 (R = H, Et, R = H) and the corresponding 2,3-dihydroindoles 126 (Eq. (5)) (96JCS(P2)241). Consistent with this interpretation, the corresponding semiquinone from cyclodopa 124 (R = H, R = COj) disproportionates into dopachrome 125 (R = H, R = COp and 

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