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I am currently working on the following problem, but I don’t know how it is solved:

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I guess it is a Fischer-Indol synthesis, but I am not sure. This is what I got:

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Any help would really be appreciated^^

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    $\begingroup$ If your study of chemistry advanced to the level to address questions like the one presented, familiarize yourself with an editor to sketch the reaction schemes, and to export the scheme as a .png you may upload here (limit: 2MB). Some of them are compared here. If your institution does not offer a campus license, e.g., ChemDraw and Marvin offer sketchers with less functionality yet running from a web browser (no installation). $\endgroup$
    – Buttonwood
    Nov 24 '21 at 12:47
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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]

G. Stork and J. E. Dolfini, J. Am. Chem. Soc., 1963, 85, 2872.

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  • $\begingroup$ If you thought that a Fischer indole synthesis was involved, you should have made some effort in that direction. $\endgroup$
    – user55119
    Nov 25 '21 at 0:34
  • $\begingroup$ @user55119 Speculation: The OP did not recognize the tautomeric relationship between compounds 2 and 3. $\endgroup$
    – Buttonwood
    Nov 25 '21 at 7:46
  • $\begingroup$ @user55119 Good answer. I was not aware of this work. Is it known whether the isomeric indole is also formed in the reaction from 1a? $\endgroup$
    – Waylander
    Nov 25 '21 at 8:03
  • $\begingroup$ @Waylander: After acetylation the paper states"...gave a crude material from which aspidospermine..." I suspect that some indole was formed. But then again, that was 58 years ago. My memory is good but not that good. ;) $\endgroup$
    – user55119
    Nov 25 '21 at 14:21
  • $\begingroup$ @user55119 and the analytical methods of the time may have struggled to find it if it was present in small amounts $\endgroup$
    – Waylander
    Nov 25 '21 at 14:41
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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.

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