I am currently working on the following problem, but I don’t know how it is solved:
I guess it is a Fischer-Indol synthesis, but I am not sure. This is what I got:
Any help would really be appreciated^^
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The question you pose is the work of Stork and Dolfini that led to the synthesis of aspidospermine 7 and quebrachamine 9. The aminoketone 1a was condensed with either phenylhydrazine or o-methoxyphenylhydrazine to form the respective arylhydrazones 2a and 2b. Exposure of either hydrazone to hot acetic acid led to a "Fischer indole synthesis" that produced the indolenines 6a and 6b. Reduction of indolenine 6b with LiAlH4 followed by acetylation afforded d,l-aspidospermidine 7, whose stereochemistry was not known at the time. Reduction of indolenine 6a with KBH4 effected reduction of immonium salt 8 (blue arrows) leading to d,l-quebrachamine 9,
One might ask why a normal Fischer indole synthesis did not occur by having the imine double bond of hydrazone 2 tautomerize toward the methylene group of the tricyclic ring moiety. My recollection, having been in this laboratory at the time, was that this issue was a problem when the sequence of reactions was run on the ketolactam 1b. [@Waylander]
Fischer Indole for the first step looks possible depending on reaction conditions, but this source states that the indole nucleus is not reduced by LiAlH4, nor do I recall ever seeing it done. Therefore I think what is happening is formation of the phenylhydrazone followed by reduction to the 1,2 di-substituted hydrazine.