Indole 3-alkylation

[Rhodium]

For example, 2-dimethylaminoethanal would give DMT, and alpha-bromo-acetaldehyde would give 3-(2-bromoethyl)-indole, which in turn would be ready for alkylation by any dialkylamine to give the corresponding N,N-dialkyltryptamine.

A general method for C3 reductive alkylation of indoles
Anu Mahadevan,Howard Sarda, Mario Gonzalez, John C. McKew

Tetrahedron Letters 44(24), 4589-4591 (2003)

(https://www.thevespiary.org/rhodium/Rhodium/pdf/reductive.3-alkylation.indoles.pdf)
DOI:

10.1016/S0040-4039(03)01010-4

Abstract

General indole C₃ reductive alkylation conditions have been developed. The scope of this reaction includes C₂ unsubstituted indoles, aryl and alkyl aldehydes, as well as N–H and N-alkyl indole substrates.

[Rhodium]

Their examples does not include nitro-alkenes, but all alkenes with any electron-withdrawing group whatsoever worked in  their synthesis, so it is highly likely that this can be used to produce 1-(3-indolyl)-2-nitropropenes in a single step from indoles and 3-acetoxy-2-nitro-propene. This can in turn is made by condensing formaldehyde with nitromethane (yielding 2-nitro-propane-1,3-diol), acetylating the diol with Ac₂O or AcCl and distilling in vacuo to give the nitroalkene (se refs at the bottom).

Palladium-catalyzed functionalization of indoles with 2-acetoxymethyl substituted electron-deficient alkenes
Shengming Ma, and Shichao Yu, Tet. Lett. 45(45), 8419-8422 (2004), DOI:

10.1016/j.tetlet.2004.08.178

Abstract
A new functionalization of indoles via palladium-catalyzed reaction of indoles and 2-acetoxymethyl substituted electron-deficient alkenes is reported. The reaction was carried out under neutral condition and no isomerization of the carbon–carbon double bond was observed.




Preparation of 3-acetoxy-2-nitro-propene:

Nitromethane + Formaldehyde --1:NaOH--2:Acetylation--> 3-acetoxy-2-nitro-propene
M.B. Frankel, Tetrahedron Suppl. 4, 213-217 (1963)

2-nitro-propane-1,3-diol + acetyl chloride --CH₂Cl₂--> 1,3-diacetoxy-2-nitro-propane --180°C/70-100mmHg--> 3-acetoxy-2-nitro-propene
Klager,K.; Monatsh. Chem. 96, 1-8 (1965)

2-nitro-propane-1,3-diol + acetic acid anhydride -> 1,3-diacetoxy-2-nitro-propane
Carbohydr. Res. 310(3) 191-202 (1998)