2,3-Disubstituted Indole Synthesis via Boronic Ester Intermediary
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Solution Overview
Problem
Existing methods for synthesizing 2,3 disubstituted indoles, such as Processes A and B, face limitations including polymerization side reactions and poor efficiency when dealing with arylbromide or vinyl bromide/vinyliodide moieties, necessitating the development of a new process for optimal production.
Innovation Solution
A process involving the reaction of a bromoindole compound with a dialkoxyl C1-5 borane or trialkyl magnesiate in the presence of a palladium catalyst and a base, followed by treatment with a borate, to produce 2,3 disubstituted indoles, allowing for the formation of desired products with improved efficiency and reduced side reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If Process A (dipyridyl zinc intermediate and palladium catalyst) is used to synthesize 2,3 disubstituted indoles, then the coupling of substituents at 2,3 positions can be achieved, but polymerization side reactions occur when the product contains arylbromide moiety
Solution Approach 1:
The patent employs a boronic ester intermediate in a Suzuki coupling reaction as an alternative to the dipyridyl zinc intermediate. This intermediary approach allows the coupling reaction to proceed without the nucleophilic zinc reagent that causes polymerization of arylbromide-containing products, thus resolving the contradiction between coupling efficiency and polymerization side reactions.
2Ease of manufacture
If Process B (Pd-catalyzed indolization of 2-bromo- or chloro-anilines with internal alkynes) is used, then 2,3 disubstituted indoles can be prepared, but efficiency deteriorates when substituents contain vinyl bromide, vinyliodide, arylbromide or aryliodide due to competing oxidative insertion
Solution Approach 1:
The patent uses a boronic ester intermediate that undergoes Suzuki coupling with aryl halides, replacing the direct Pd-catalyzed indolization method. This intermediary boronic ester approach prevents competing oxidative insertion reactions of vinyl bromide, vinyliodide, arylbromide, and aryliodide substituents with the palladium catalyst, thereby maintaining high reaction efficiency while preserving synthesis capability.
3Quantity of substance
If existing synthesis processes are used, then 2,3 disubstituted indoles can be produced, but side reactions and reduced efficiency occur with specific functional groups
Solution Approach 1:
The patent changes the reaction parameters by employing Suzuki coupling conditions with boronic esters, palladium catalysts, and specific bases instead of the previous methods. This parameter change enables high-yield synthesis of 2,3 disubstituted indoles while maintaining high selectivity even when substrates contain sensitive functional groups like vinyl bromide, vinyliodide, arylbromide, or aryliodide, thus resolving the contradiction between product yield and reaction selectivity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This new process enhances the synthesis of 2,3 disubstituted indoles by avoiding polymerization and improving efficiency, making them suitable as pharmaceutical agents, particularly for treating hepatitis C viral infections.
Implementation Method 1
reacting a bromoindole compound (i) with a dialkoxyl C1-5 borane in the presence of a ligand, a palladium catalyst and a base
Data Source
AI summary
Disclosed are processes for making 2,3 disubstituted indole compounds such as compounds of general formula I comprised of the steps ofa) reacting a bromoindole compound (i) with a dialkoxyl C1-5 borane in the presence of a ligand, a palladium catalyst and a base to make a compound of general formula (ii); or alternatively reacting compound (i) with a trialkyl magnesiate reagent, followed by treatment with a borate;b) reacting the product of step a with a R2-Hal where R2-Hal is defined herein.