Highly enantioselective Michael addition of malonate derivatives to enones catalyzed by an N,N'-dioxide-scandium(III) complex.

Abstract

The catalytic asymmetric conjugate addition reaction is one of the most powerful methods for the carbon carbon bond formation because various chiral functionalized adducts can be obtained from numerous Michael acceptors and donors. Among them, the asymmetric Michael addition of 1,3-dicarbonyl compounds to enones provides a simple way for the preparation of synthetically useful 1,5-dicarbonyl compounds and attracts more and more chemists interests. There have been several catalysts developed for this reaction, such as chiral metal complexes, chiral ammonium salts, chiral amine catalysts and thiourea catalysts, but only few reports appeared successfully when chalcone derivatives were used as Michael acceptors. Despite excellent enantioselectivity have been achieved by Maruoka, Wang and Kobayashi et al., developing new and efficient chiral catalyst systems is still in great need. Recently, N,N’-dioxide–metal complexes have been successfully applied to promote many kinds of asymmetric transformations, herein we wish to report a highly enantioselective Michael addition of malonate derivatives to chalcone derivatives catalyzed by l-Ramipril acid derived N,N’-dioxide– scandiumACHTUNGTRENNUNG(III) complex. A wide range of substrates can be tolerated, affording the desired products with up to 99% yield and 99% ee. Inspired by our previous studies, we initiated the experiment by using l-Ramipril acid derived N,N’-dioxide L1– nickel(II) complex to catalyze the asymmetric Michael addition of diethyl malonate 1a to chalcone 2a in EtOH at 35 8C. However, only racemic product 3a was obtained. Then serveral other Lewis acids, such as Cu, Zn, La, Y, Sc salts were investigated, which were known to be chelated well with dicarbonyl compounds. As summarized in Table 1, scandium triflate was found to be superior to all the other metals tested, producing 3a in good yield with 91% ee (Table 1, entries 1–6). Encouraged by the results, scandium triflate was selected as the central metal for further research. Then a series of N,N’-dioxides was synthesized and combined with scandium triflate to promote the conju-

DOI: 10.1002/chem.200901157

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Cite this paper

@article{Chen2009HighlyEM, title={Highly enantioselective Michael addition of malonate derivatives to enones catalyzed by an N,N'-dioxide-scandium(III) complex.}, author={Donghui Chen and Zhenling Chen and Xiao Xiao and Zhigang Yang and Lili Lin and Xiaohua Liu and Xiaoming Feng}, journal={Chemistry}, year={2009}, volume={15 28}, pages={6807-10} }