Selective Reductive Amination of Ketomorphinans
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Solution Overview
Problem
Current methods for synthesizing N-alkylated ketomorphinans require protection and de-protection of the ketone group, leading to inefficiencies and incomplete reduction, and existing reductive alkylation processes often result in the reduction of carbonyl compounds to alcohols, necessitating the use of stoichiometric reagents and generating boron or aluminum salts.
Innovation Solution
A process involving the selective catalytic hydrogen transfer reduction of N-imine or hemiaminal ketomorphinans, maintaining the ketone group as unprotected, using a hydrogen source produced in situ and a catalyst, which reduces the N-imine moiety to the corresponding alkyl group without substantially reducing the ketone functionality to an alcohol.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional reductive alkylation methods are used with unprotected ketone groups, then the reductive amination can proceed directly, but the carbonyl group is reduced to alcohol instead of being preserved
Solution Approach 1:
The patent changes the chemical parameters of the reduction system by using formic acid/triethylamine adduct as a hydrogen source instead of traditional hydride reagents, and employs a ruthenium catalyst with specific ligands to achieve selective reduction of the imine group while preserving the ketone functionality. This parameter change enables direct reductive amination without protection while maintaining manufacturing precision.
Solution Approach 2:
The patent introduces a catalyst system (ruthenium complex with activating ligand) as an intermediary that mediates the selective reduction process. The catalyst enables the formic acid/triethylamine adduct to transfer hydrogen selectively to the imine group, preventing unwanted reduction of the ketone group while facilitating the desired reductive amination.
2Productivity
If stoichiometric reducing reagents are used to achieve complete reduction, then the reduction can be complete, but boron or aluminum salts are released from the product
Solution Approach 1:
The patent replaces traditional stoichiometric reducing reagents (mechanical/chemical reagents like borohydride or aluminum hydride) with a catalytic system using formic acid/triethylamine adduct as a hydrogen source and a ruthenium catalyst. This substitution eliminates the release of boron or aluminum salts while maintaining complete reduction efficiency, thereby removing harmful salt contamination.
Solution Approach 2:
The patent changes the reduction mechanism from stoichiometric reagent-based reduction to catalytic hydrogen transfer reduction. By using a catalyst with a hydrogen source, the process achieves complete reduction without requiring stoichiometric amounts of reagents, thus avoiding salt contamination while maintaining productivity.
3Manufacturing precision
If protection and de-protection steps are added to preserve the ketone group, then the ketone functionality is preserved, but the synthesis process becomes less efficient
Solution Approach 1:
The patent changes the selectivity parameters of the reduction system by employing a ruthenium catalyst with specific activating ligands that enable selective reduction of the imine group in the presence of an unprotected ketone group. This parameter change allows the ketone to remain unprotected throughout the process, eliminating protection and de-protection steps while maintaining manufacturing precision.
Solution Approach 2:
The catalyst system acts as an intermediary that provides selectivity to the reduction process, enabling the ketone group to remain unprotected while still achieving selective reduction of the imine group. This intermediary function eliminates the need for protection steps, thereby improving productivity without sacrificing manufacturing precision.
4Productivity
If Noyori catalyst with activating ligand is used for reductive amination, then the reductive amination proceeds, but the 6-keto group is reduced to alpha-hydroxy-epimer
Solution Approach 1:
The patent modifies the catalyst parameters by using a ruthenium catalyst with specific ligands that change the selectivity profile of the reduction process. This parameter change allows the catalyst to reduce the imine group rapidly while preventing reduction of the ketone group, thereby maintaining both high productivity and manufacturing precision that were previously contradictory.
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 method allows for the efficient and high-yield synthesis of N-alkylated ketomorphinans while preserving the ketone group, eliminating the need for protection and de-protection steps and reducing the generation of unwanted salts, thereby improving the synthetic efficiency and yield.
Implementation Method 1
reducing the N-imine moiety or a hemiaminal moiety in the presence of a hydrogen source produced in situ through hydrogen transfer and a catalyst
Implementation Method 2
reducing the N-imine moiety or a hemiaminal moiety in the presence of a hydrogen source produced in situ through hydrogen transfer and a catalyst
Implementation Method 3
reducing the N-imine ketomorphinan or hemiaminal ketomorphinan without substantially reducing the 6-keto functionality to an alcohol
Data Source
AI summary
The present invention is generally directed to a process for the preparation of a ketomorphinan comprising maintaining a ketone group as unprotected and performing reductive amination using a hydrogen source and a catalyst.