Elsevier

Tetrahedron Letters

Volume 53, Issue 40, 3 October 2012, Pages 5445-5448
Tetrahedron Letters

Aldol condensation of amides using phosphazene-based catalysis

https://doi.org/10.1016/j.tetlet.2012.07.129Get rights and content

Abstract

We have developed a new method for the direct aldol condensation of unactivated amides using 1,3,5-triazo-2,4,6-triphosphorine-2,2,4,4,6,6-hexachloride (TAPC)-based phosphorous/SO42− catalysis. The SO42− species in a reaction mixture enhances the reaction rate of the catalysis. In principle, no metal sources are required for the generation of the catalyst, and there is no requirement for the use of stoichiometric quantities of an acid or base. This catalyst system is operative under relatively acidic conditions. One major advantage of carrying out the reaction under acidic conditions is that both aldehydes and acetals are capable of undergoing carbon–carbon bond formation at the α-carbon of amide carbonyl groups through dehydration.

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Acknowledgments

This work was supported by a Grant-in-Aid for Scientific Research B (General) from JSPS and Scientific Research on Priority Areas ‘Advanced Molecular Transformations of Carbon Resource’ from MEXT. S.W.F. was supported by the GCOE in chemistry, Nagoya University (NU). The authors wish to thank Dr. K. Oyama and Y. Maeda (Chemical Instrumentation Facility of RCMS) for NMR and ESI-MS measurements and Professor R. Noyori (NU & RIKEN) for fruitful discussions.

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