Palladium-Catalyzed Synthesis of 3-Indolecarboxylic Acid Derivatives

Abstract

Indoles having an ester functionality in the 3-position were prepared from 2-(2-nitrophenyl)propenoic acid derivatives via a palladium-catalyzed reductive N-heteroannulation using carbon monoxide as the ultimate reducing agent. The starting materials were prepared either by a Stille coupling of 2-halo-1-nitrobenzenes with ethyl 2-(tributylstannyl)-2-propenoate or by vicarious nucleophilic substitution of nitrobenzenes followed by a Knoevenagel-type condensation with an aldehyde. Synthesis of an example of a 3-nitrile- and a 3-sulfone-substituted indole is also described using the same type of methodologies.

Key words

palladium - catalysis - reductions - indoles - cyclizations

References

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31

One carbon resonance was not observed.

39

The reported mp for the dimethyl diester is 143-144 °C.