Nenitzescu indole synthesis Mechanism

The bona fide mechanism of the Nenitzescu indole synthesis involves complicated, multiple redox cycles. A simplified version is shown below ... 

Two kinds of mechanisms are possible for the Nenitzescu indole synthesis, depending on the order of carbon-carbon bond and carbon-nitrogen bond formation. " However, the one involving the initial carbon-carbon condensation is more plausible as illustrated here for the reaction between 2-methyl 1,4-benzoquinone and 0-amino methyl crotonate. ... 

Scheme 6 Stack s Proposed Mechanism of the Nenitzescu Indole Synthesis...

Scheme 3 Nenitzescu and Allen Mechanism for this Indole Synthesis...

Only a few indole syntheses make use of building blocks in which the N-atom is not directly bonded to an arene. The Nenitzescu synthesis is of this type. In this synthesis, 1,4-quinones are condensed with 3-aminoacrylic esters to give 5-hydroxyindole-3-carboxylic esters 44. The mechanism of this synthesis has not been completely clarified. It includes a Michael addition (-> 41) and a cyclodehydration (42 43) as well as a redox transformation (41 42 and 43 44) [53] ... 

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