Chemo- and stereoselectivity in titanium-mediated regioselective ring-opening reaction of epoxides at the more substituted carbon |
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Authors: | Tetsuaki Tanaka Kei Hiramatsu Yasutaka Kobayashi Hiroaki Ohno |
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Institution: | Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamadaoka, Suita, Osaka 565-0871, Japan |
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Abstract: | Chemo- and stereoselectivity in the ring-opening reaction of epoxides with a reagent prepared from allylmagnesium halide and chlorotitanium triphenoxide is described. It has been proven that the allylating reagent can also be used for the reaction of epoxides bearing a tert-butyl ester, amide, or acetal moiety, and that the epoxide cleavage regioselectively takes place at the more substituted carbon in all cases. Interestingly, while the reaction of acyclic 2,2,3-trialkyl epoxides or 3,3-disubstituted 2,3-epoxy alcohol derivatives with the allyltitanium reagent yielded the allylated products as an almost 1:1 diastereomixture, the ring-opening reaction of 2-substituted 2,3-epoxy alcohol derivatives stereospecifically proceeded through the anti pathway. The latter reaction is extremely useful for asymmetric construction of quaternary carbon centers. |
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Keywords: | Epoxides Titanium Allylation Quaternary carbon |
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