Fischers Bases from Oxindoles

A unique oxindole synthesis is the addition of diphenylketene to the mono-A-phenylimine of benzoquinone the resulting spiro-P-lactam (18) rearranges to give a 62% overall yield of 5-hydroxy-l,3,3-triphenyloxindole (19), which can be methylated to the 5-methoxy compound,35 which in turn could be converted to the Fischer s base. 

Trimethyloxindole is usually prepared by permanganate oxidation of Fischer s base.36 Cyanine, merocyanine (including spiropyran), and styryl dyes made from Fischer s base also give the oxindole upon thermal or photodegradation in air. The accumulated pot residues from the distillation of Fischer s base and the concentrates from dye preparations can be recycled by simply treating these chemical wastes with air (or better, hydrogen peroxide), preferably in the presence of visible light. The trimethyloxindole is recovered by a simple vacuum distillation in about 50% yield (from Fischer s base still residues).7 

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Improved syntheses based on classical routes such as the Fischer indolization route and the oxindole alkylation route have also been reported. The former could provide substantial amounts of the racemic alkaloids, while the latter made possible the practical production of both the natural and the unnatural enantiomers of the alkaloids with the development of a highly efficient method for resolving the racemic intermediate. The latter may be particularly interesting from the pharma-... 

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