Indoxyl ring synthesis

Peroxide oxidation of Af-phenylsulfonylindole-3-boronic acid gives A -phenylsulfonylindoxyl, which can be converted into the triflate of the 3-hydroxyindole tautomer. The same A -protected indoxyl can be prepared by ring synthesis, as shown below. 

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... 

It is possible to directly chloroacylate an aniline using chloroacetonitrile and boron trifluoride, ortho to the nitrogen. After (V-acylation, ring closure produces iV-acetyl-indoxyls. The Sugasawa synthesis of indoles utilises these same orf/to-chloroacetyl-anilines, via borohydride reduction and ring closure. ... 

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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