Indoxyl derivatives, synthesis

Graiya Y, Ramana CV (2013) Synthesis of pseudo-indoxyl derivatives via sequential Cu-catalyzed SNAr and Smalley cyclization. Chem Commun 49(57) 6376-6378... 

In the synthesis due to Heumann and Pfleger the fusion yields the potassium derivative of indoxyl, which is dehydrogenated to indigo even by atmospheric oxygen at the same time hydrogen peroxide is produced (see p. 175). 

There are numerous additional studies based on the properties of enam-ines and the synthesis of the pyrrole ring. Thus, fusion of dienetriamines formed by a reaction of aminals of a,/3-unsaturated /3-dimethylaminoalde-hydes (41) with /V-acetylindoxyl results in cyclization to pyrroloindoles (42) (87IZV821). Dienetriamino derivatives of a different type (43) obtained from indoxyl are also transformed into pyrrolo[l, 2-a]indoles (44) upon... 

An important variation of the Jones-Schmid indole synthesis is the base-mediated cyclization onto esters, which affords 3-hydroxyindoles (indoxyl tautomers) under mild conditions. Three case studies are shown in Scheme 2 (equations 1-3) [18-20]. This chemistry, like that in Table 1 (Entries 4-11), represents a powerful route to C-3 functionalized indoles. Kraus and coworkers use the steri-cally hindered phosphazine base, P -t-Bu, to prepare the 5,6-dihydroindolo[2,l-a]isoquinoline ring system (equation 4) [21]. Several derivatives display immunosuppressive activity. 

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