Enantioselective Addition of Cyclic Enol Silyl Ethers to 2-Alkenoyl-Pyridine-N-Oxides Catalysed by Cu(II) -Bis(oxazoline) Complexes |
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Authors: | Alessandro Livieri Massimo Boiocchi Giovanni Desimoni Giuseppe Faita |
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Institution: | Department of Organic Chemistry, University of Pavia, V. le Taramelli, 10; 27100 Pavia (Italy), Fax: (+39)?0382-987323. |
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Abstract: | Asymmetric reactions involving (E)-3-aryl-1-(pyridin-2-yl-N-oxide)prop-2-en-1-ones and cyclic enol silyl ethers show good yields and excellent enantioselectivities (up to 99.9?% ee) when catalysed by bis(oxazoline)-Cu(II) complexes. Different reaction pathways can be followed by different enol silyl ethers: with 2-(trimethylsilyloxy)furan, a Mukaiyama-Michael adduct is obtained, whereas a hetero Diels-Alder cycloadduct was formed by using (1,2-dihydronaphthalen-4-yloxy)trimethylsilane. In the latter reaction, the absolute configuration of the product is consistent with a reagent approach to the less hindered Re face of the coordinated substrate in the reactive complex. |
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