Wow! Nitroethene is sufficiently electrophilic to substitute indole without the need of acid catalyst, the yield is 80% at room temperature:

https://www.thevespiary.org/rhodium/Rhodium/hive/hiveboard/picproxie_docs/000444232-file_fm8i.jpg" title="View this image">

I'll bee back with the detailed experimental procedure...

Yup, it is - a lot of Repke's publications use this synthon for making tryptamines. 1-Dimethylamino-2-nitroethene (DMANE) is also pretty good:

https://www.thevespiary.org/rhodium/Rhodium/chemistry/dmane.html

Tryptamine,  synthesis starting with nitroethylene and indole:  Noland, Hartman, J. Am. Chem. Soc. 76, 3227 (1954)

The Nitroethylation of Indole. A New Synthesis of Tryptamine.
Wayland E. Noland, Philip J. Hartman

J. Am. Chem. Soc. 76(12), 3227-3228 (1954)

(https://www.thevespiary.org/rhodium/Rhodium/pdf/tryptamine.indole.nitroethylation.pdf)

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Edit: I have backed up the great article from pHarmacist's post below to my page for safekeeping:

JOC 45, 1185-1189 (1980)

(https://www.thevespiary.org/rhodium/Rhodium/pdf/nitroethene.in.organic.synthesis.pdf)

Nitroethylene: A Stable, Clean, and Reactive Agent for Organic Synthesis

J . Org. Chem. 1980,45, 1185-1189
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Full-text:

http://pharmacist8.tripod.com/jo01295a003.pdf