Great synthetic approach to 4-subst. indoles

[pHarmacist]

Fellow Tryptamine Bees!

This is an interesting reduction of indole with Li in the presence of trimethylsilyl chloride, followed by rearomatisation that give you 4-methylsilylindole – an excellent intermediate used in the synthesis of 4-substituted indoles via electrophilic replacement of silicon.

Preparation and Reactions of 4-(Trimethylsilyl)indole
Anthony G. M. Barrett, Daniel Dauzonne, Ian A. O'Neil, Alain Renaud

J. Org. Chem. 49, 4409-4415 (1984)

(https://www.thevespiary.org/rhodium/Rhodium/pdf/4-tms-indole.synthesis.and.reactions.pdf)

Abstract:

Indole or 1-(trimethylsilyl)indole was reacted sequentially with lithium-chlorotrimethylsilane and with 1,4-benzoquinone to produce 1,4-bis(trimethylsilyl)indole (50% and 55%, respectively). Methanolysis gave 4-(trimethylsilyl)-indole which reacted with electrophiles at C-3. However, the derivative l-acetyl-4-(trimethylsilyl)indole reacted with acetyl, 2-chloropropanoyl, or propenoyl chlorides via clean C-4 ipso substitution. Attempts to extend the reaction to a useful synthesis of derivatives of 5-oxo-1,3,4,5-tetrahydrobenz[cd]indole, a lysergic acid synthon, were prevented by low yields.
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See also:

Post 443497

(pHarmacist: "Large-scale syntheses of Psilocin/Psilocybin", Tryptamine Chemistry)

[pHarmacist]

Failed to find this using TFSE, if posted b4 - delete:

The Synthesis of S-Keto-l,3,4,5-tetrahydrobenz[cd]indole. A Synthesis of 4-Substituted Indoles
Frederick C. Uhle

JOACS VOLUME 71 MARCH 19, 1949 NUMBER 3

(http://pharmacist-hive.tripod.com/uhle.pdf)

[pHarmacist]

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                              [ P r e s e n t s ]

Ah, our old friend Sandmeyer  



Palladium-catalyzed reactions in the synthesis of 3- and 4-substituted indoles. Approaches to ergot alkaloids
Peter J. Harrington, Louis S. Hegedus;

J. Org. Chem.; 1984; 49(15); 2657-2662.

(http://pharmacist-hive.tripod.com/4-subst-indol-ergot.pdf)

Abstract: An efficient synthesis of 4-bromo-1-tosylindole (10) based on the Pd(II)-catalyzd cyclization of an o-ethenylaniline p-toluenesulfonamide has been developed. A Pd(0) oxidative addition-olefin insertion-B-hydride elimination cycle converted 10 to a number of 4-substituted 1-tosylindoles. Selective electrophilic substitutions at the 3-position of 10 provided access to the 3-(chloromercurio)- (18) and 3-iodo-l-tceylindoles (22). Transmetalation to palladium and allyl chloride insertion converted 18 to 3-allyl-4-bromo-1-tosylindole (20) which could be cyclized to the benz[c,d]indoline 21. A Pd(0) oxidative addition-olefin insertion-@-hydride elimination cycle converted the 3-iodo compound 22 to a number of 4-bromo-3-substitutd 1-tosylindoles including 24, a potential precursor to optically active tryptophans.

Fellow tryptamine bees, enjoy and expect more on 4-subst indoles!

[hest]

Hi PH..
Good to see someone looking at this wonderfull indole.
Doo you have a good way to the 2,6-nitro-toluene ?
Dinitration of toluene and seperation of the isomeres have alwayes seem a bid diff. to mee.
The Azide routhe from salicylaldehyde i still my favorite.

[Rhodium]

What about dinitrating para-toluenesulfonic acid, then desulfonate?