Mild and Practical Indole C2 Allylation by Allylboration of in situ Generated 3‐Chloroindolenines

Abstract

C2 allylation of indole derivatives is a challenging but important transformation given the biological relevance of the products. Herein we report a selective C2 allylation strategy that proceeds via allylboration of in situ‐generated 3‐chloroindolenines. The reaction is mild, practical, and compatible with a wide range of C3‐substituted indoles. As allylboronates are readily accessible from commercial precursors, various substituted allyl moieties can be introduced using the same protocol. To showcase the utility of this method we applied it to the synthesis of the natural product, tryprostatin B.

CTAB-assisted synthesis of reduced graphene oxide supported Pd nanoparticles(Pd@rGO) as a sustainable heterogeneous catalyst for C-2 arylation of indoles with arylboronic acids.

“…Cheng and co-workers have reported aryltri uoroborate salts as coupling partners in the presence of Pd(OAc) 2 and Cu(OAc) 2 in the air (Zhao et al, 2008). Despite the signi cant advantages, most of the protocols are still suffering from several issues such as harsh reaction conditions, expensive metal catalysts, multi-step catalyst synthetic procedures, acidic solvents, high reaction temperature, long reaction time, limited functional group tolerance, as well as a narrow substrate scope and homogenous catalytic systems in many cases causing di culty in catalyst recovery and reuse (Bhattacharjee et al 2020, Figueiras et al 2022, Saya et al 2019, Yun et al 2020. Therefore, the direct C-H arylation of indoles continues to be a crucial challenge, and opportunities for developing mild and e cient protocols are abundant.…”

Catalytic C2 prenylation of unprotected indoles: Late-stage diversification of peptides and two-step total synthesis of tryprostatin B

“…Tryprostatin B is a prominent C2 prenylated natural indole alkaloid. The groups of Danishefsky [21,22], Cook [26], Lobo and Prabhakar [24,25], Fukuyama [67,68], Ruijter [23], and Hossain [27] have contributed to its total synthesis. In their works, C2 prenyl decoration was accomplished at the early-stage.…”

“…A combination of tert-prenyl boronate and NCS could make the reaction conditions milder (Fig. 2(a), (i)) [23]. Alternatively, the prenyl group could be installed via an acid-promoted rearrangement of pre-formed N-prenylated indole (Fig.…”