First Total Synthesis of Reassigned Echinosulfonic Acid D

Abstract

Echinosulfonic acid D, a sponge metabolite whose structure was recently reassigned, was synthesized for the first time. The key step is the double indolization of dimethylbarbituric acid using the umpolung indole reagent, followed by a hydrolysis/decarboxylation/esterification sequence.

On Demand Synthesis of C3−N1’ Bisindoles by a Formal Umpolung Strategy: First Total Synthesis of (±)‐Rivularin A

“…Subsequently, the C3−N1’‐indole‐indolines 5 were prepared through the oxidation using MnO 2 [14] in DCE at 50 °C. Deprotection of Ts group were also achieved by NaOH, [15] delivering the NH‐free C3−N1 bisindoles. It is noteworthy that 3‐ or 2‐substituted C3−N1 bisindoles 6 al and 6 am could successfully be synthesized in 34 % and 37 % yields, respectively, for 3 steps from 3 al and 3 am .…”

Aluminum-Catalyzed Cross Selective C3–N1′ Coupling Reactions of N-Methoxyindoles with Indoles

“…Over the past five years, our group has had an intensive focus on the development and application of umpoled indole surrogates [33][34][35][36][37][38][39][40][41][42][43][44]. These results led us to find that in situ generated 3-methoxyindoles act as a C3-electrophilic reagent that can be harnessed for C-N, C-O, and C-C bond-forming SNAr reactions under indium catalysts [45,46].…”

“…By analogy to our indium-catalyzed SNAr reaction, we hypothesized that N-alkoxy indoles might be suitable competent substrate as a N1-electrophilic indole precursor by a Lewis acid activation of alkoxy group through an elimination of ROH, thereby producing a C3-N1′ bisindole (Scheme 2). In this hypothesis, N-alkoxyindole is first combined with Lewis acids (LA) to form an LA-indole complex, which shows an N-electrophilic character by N-O bond activation along with reducing C3-nucleophilicity by coordinating at the C2-C3 π-bond [47- Over the past five years, our group has had an intensive focus on the development and application of umpoled indole surrogates [33][34][35][36][37][38][39][40][41][42][43][44]. These results led us to find that in situ generated 3-methoxyindoles act as a C3-electrophilic reagent that can be harnessed for C-N, C-O, and C-C bond-forming S N Ar reactions under indium catalysts [45,46].…”

Oxytrofalcatin Puzzle: Total Synthesis and Structural Revision of Oxytrofalcatins B and C

“…To avoid this complicated issue, we decided to focus on oxytrofalcatin C ( 3 ), which is an enol-ether indole alkaloid. Based on our interest in misassigned natural products and indole alkaloid synthesis, we envisage that determination of the real structure of oxytrofalcatin C is worth investigating.…”