Enantioselective Addition of Cyclic Enol Silyl Ethers to 2‐Alkenoyl‐Pyridine‐N‐Oxides Catalysed by CuII–Bis(oxazoline) Complexes |
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Authors: | Dr Alessandro Livieri Dr Massimo Boiocchi Prof Giovanni Desimoni Prof Giuseppe Faita |
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Institution: | 1. Department of Organic Chemistry, University of Pavia, V. le Taramelli, 10;2. 27100 Pavia (Italy), Fax: (+39)?0382‐987323;3. Centro Grandi Strumenti, University of Pavia, V. Bassi, 8;4. 27100 Pavia (Italy) |
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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)–CuII 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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Keywords: | asymmetric catalysis copper cycloaddition enol silyl ethers Mukaiyama reactions nitrogen heterocycles |
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