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DOI: 10.1055/s-2008-1042721
Polymer-Supported Hantzsch Ester as An Efficient Hydrogen Source
Contributor(s):Benjamin List, Lars RatjenNational University of Singapore and the University of Hong Kong, P. R. of China
Polymer-Supported Hantzsch 1,4-Dihydropyridine Ester: An Efficient Biomimetic Hydrogen Source
Adv. Synth. Catal. 2008, 350: 54-60
Publication History
Publication Date:
21 February 2008 (online)
Key words
polymer-supported synthesis - reduction - Hantzsch esters - biomimetics
Significance
The authors report an immobilization strategy for the Hantzsch ester as a heterogeneous hydrogen source. The direct microwave-assisted synthesis of the Hantzsch ester on pre-formed polymerous support 1 gave the active polymeric species 2. This polymer was a very efficient hydrogen source in different reactions, such as the reduction of α,β-unsaturated aldehydes 3 (yields up to 93%), the reductive amination of aldehydes 4 (yields up to 99%), and also the aromatization of DDQ 5 (99% yield). Surprisingly the reactions were very fast, also in comparison with homogeneously conducted transformations. The easy reaction workup, that the authors call ‘mix, filter and evaporate’ is alike highly remarkable.
Comment
The approach provided by the authors enlarges the growing field of polymer-supported organic synthesis with an important tool. The polymer-supported Hantzsch ester is not only a powerful reductive agent, but also an example for a heterogeneous biomimeticum. In combination with an organocatalyst it can copy the features of naturally occurring molecules, such as NADH or FADH2. The fact that the achieved results are comparable or better than under homogeneous conditions, illustrates the usefulness of the procedure.