Aripiprazole Synthesis via Friedel-Crafts Alkylation and Phase Transfer Catalysis
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Solution Overview
Problem
Existing processes for preparing aripiprazole suffer from low yields, formation of impurities, and cumbersome workups, which hinder the efficient production of this psychotropic drug.
Innovation Solution
A novel process involving intramolecular Fridel-Craft alkylation of N-(3-methoxyphenyl)-3-chloropropionamide to produce 7-hydroxy-3,4-dihydro carbostyril, followed by reaction with 1-bromo-4-chlorobutane using a phase transfer catalyst, and subsequent condensation with l-(2,3-dichlorophenyl)piperazine in the presence of sodium iodide and potassium carbonate, optimizing conditions for high yield and purity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional processes are used for preparing aripiprazole, then the synthesis can be completed, but the yield is low and impurities are formed
Solution Approach 1:
The patent employs parameter changes by optimizing reaction conditions including using specific Lewis acids (AlCl3, FeCl3, TiCl4, SnCl4, BF3) as catalysts, conducting reactions at elevated temperatures (120-160°C), and using dimethyl acetamide (DMA) as solvent. These parameter optimizations systematically improve both yield and purity of the Fridel-Craft alkylation step, resolving the contradiction between productivity and manufacturing precision.
2Productivity
If conventional synthesis methods are used, then aripiprazole can be produced, but cumbersome workups are required
Solution Approach 1:
The patent uses phase transfer catalysts (PTC) such as polyethylene glycol or Aliquat-336 in the alkylolation step, which act as intermediaries to facilitate the reaction between 7-hydroxy-3,4-dihydro carbostyril and 1-bromo-4-chlorobutane. This intermediary approach simplifies the workup procedure by enabling easier separation of products from reaction mixtures, thereby improving ease of operation while maintaining high productivity.
3Manufacturing precision
If existing processes are used for aripiprazole preparation, then synthesis can proceed, but impurity formation occurs
Solution Approach 1:
The patent converts potentially harmful polyalkylation side reactions into beneficial outcomes by carefully controlling reaction parameters. By using specific Lewis acids in controlled amounts (3-5 equivalents) and maintaining optimal temperatures, the process achieves high selectivity for the desired monalkylated product while minimizing impurity formation. The phase transfer catalyst similarly enhances selectivity, converting what could be harmful side reactions into beneficial pathway control.
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
The process achieves high yield and purity of aripiprazole, simplifying the synthetic steps and reducing impurity formation, thereby enhancing the efficiency of its production.
Implementation Method 1
intramolecular Fridel-Craft alkylation of N-(3-methoxyphenyl)-3-chloropropionamide (I) to give 7-hydroxy-3, 4-dihydro carbostyril (II)
Implementation Method 2
reaction of 7-hydroxy-3, 4-dihydro carbostyril (II) with 1-bromo-4-chlorobutane in the presence of a base and a phase transfer catalyst (PTC)
Implementation Method 3
condensation with l-(2,3-dichlorophenyl)piperazine in the presence of sodium iodide and potassium carbonate
Data Source
AI summary
A process for the preparation of 7-hydroxy-3,4-dihydro carbostyril (II) by intramolecular Fridel-Craft alkylation of N-(3-methoxyphenyl)-3-chloropropionamide (I) in which an equivalent of N-(3-methoxyphenyl)-3-chloropropionamide (I) is contacted with a Lewis acid (e.g. aluminium chloride) in dimethyl acetamide (DMA), at an elevated temperature of from about 120°C to about 160°C, is provided. The process produces 7-hydroxy-3,4- dihydro carbostyril (II) in high yield and a high state of purity such that it may be used in subsequent .reaction towards the preparation of aripiprazole (IV). Thus 7-hydroxy-3,4- dihydro carbostyril (II) was treated with l-bromo-4-chlorobutane under phase transfer catalyst (PTC) conditions using solvents like acetone or n-butanol at temperature ranging 25°C to 45°C to afford 7-(4-chlorobutoxy)-3,4-dihydro carbostyril (III). The PTC conditions described in this patent afford 7-(4-chlorobutoxy)-3,4-dihydro carbostyril (III) in high purity and high yield with the corresponding dimmer formation is considerably low as compared with the other literature methods of preparing 7-(4-chlorobutoxy)-3,4- dihydro carbostyril (III). Compound (III) was treated with l-(2,3-dichlorophenyl)piperazine, at temperature ranging from 50°C to 100°C, and sodium iodide, potassium carbonate, dimethyl formamide (DMF) as a solvent to afford aripiprazole in high purity and high yield.