Convenient Synthesis of Thieno[3,2‐b]indoles and Thieno[3,4‐b]indoles by Sequential Site‐Selective Suzuki and Double C–N Coupling Reactions

Abstract

A convenient synthesis of thieno[3,2‐b]indoles and thieno[3,4‐b]indoles has been developed. The protocol involves a site‐selective Suzuki reaction, followed by a double C–N coupling reaction using anilines, benzylamines, or alkylamines. The yields range from good to excellent.

Broadly Applicable Synthesis of Arylated Dithieno[3,2‐b:2′,3′‐d]pyrroles as Building Blocks for Organic Electronic Materials

“…As in the case of arylated DTPs, a broad series of corresponding thienoindoles were prepared by Langer et al. by Buchwald‐Hartwig amination of dibrominated phenylthiophene precursors and aryl amines [16] . The only example of a direct N‐arylation of DTP was this year released by Tang et al., who reacted 2‐bromonaphthoquinone and 2‐bromoanthraquinone with H −DTP 1 under Pd‐catalysis with (Pd 2 dba 3 /X−Phos) to the corresponding arylated DTPs in 40 % and 47 % yield, respectively [17] …”

Ullmann‐Goldberg and Buchwald‐Hartwig C−N Cross Couplings: Synthetic Methods to Pharmaceutically Potential N‐Heterocycles

“…The desired product 26 cannot be produced from anilines bearing strong electron-deficient substituents. [64] In another approach, the Langer research group in 2016 successfully synthesized thieno [3,2-b]indole 28 and thieno [3,4b]indole 31 derivatives by double Buchwald-Hartwig method in toluene at 100°C (Scheme 7). In this method, the precursors 27 and 30 were respectively achieved by coupling of 2,3dibromothiophene and 3,4-dibromothiophene with 2-bromophenylboronic acid via site-selective Suzuki reaction.…”

“…Applying anilines‐containing electron‐donating or slightly electron‐withdrawing substituents resulted in the corresponding product with good to high yields (Scheme 6). The desired product 26 cannot be produced from anilines bearing strong electron‐deficient substituents [64] …”

“…The reaction was performed in the presence of Pd 2 (dba) 3 and the phosphoric ligand dppf 29 as the catalytic system when electron‐rich amines were applied. For electron‐poor benzylic and aliphatic amines, BINAP 23 was employed as an efficient ligand with high outcomes [64] …”

“…For electron-poor benzylic and aliphatic amines, BINAP 23 was employed as an efficient ligand with high outcomes. [64] In the next year, this same group applied a similar method to achieve substituted indoloquinolines isomers 33 and 35, using Pd catalysts in toluene heated up to 100 °C (Scheme 8). In this approach, aniline was used as an amination agent, and the result was successfully obtained with up to 97% effectivity.…”