Large Scale Synthesis of N-Benzyl-4-formylpiperidine Through Partial Reduction of Esters Using Aluminum Hydride Reagents Modified with Pyrrolidine.
2010
Abstract The modification of sodium bis(2-methoxyethoxy)aluminum hydride (SMEAH) with pyrrolidine provided a highly selective reducing agent to transform N -benzyl-4-ethoxycarbonylpiperidine into N -benzyl-4-formylpiperidine 1 under mild conditions. However, this simple modification led to a significant amount of N -benzyl-4-(pyrrolidin-1-ylmethyl)piperidine 4 due to overreduction of an intermediate. Our extensive research revealed that an alkaline base such as potassium tert -butoxide could suppress the formation of the by-product to give the desired aldehyde, enabling us to establish a viable synthetic process for a key intermediate of donepezil hydrochloride. The potential applications of this reagent are also described.
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