Palladium-Catalyzed Regioselective [3 + 2] Cycloaddition of Vinylic Oxiranes with Activated Olefins. A Facile Synthesis of Tetrahydrofuran Derivatives
摘要:
The reaction of certain activated olefins (Michael accepters) 5 with vinylic oxiranes 1 in the presence of catalytic amounts of Pd(PPh3)(4) (5 mol %) in THF at 40 degrees C gave the corresponding [3 + 2] cycloaddition products 6. In all cases the reactions proceeded in regioselective manner, affording the corresponding polysubstituted tetrahydrofuran derivatives. The nature of electron-withdrawing group in activated olefins affected significantly the reactivity of substrates. Michael accepters having sterically less bulky electron-withdrawing groups were essential for the cycloaddition reaction, and the presence of two electron-withdrawing groups at the ct-position was needed. Accordingly, activated olefins having (CN, CN), (CN, CO2Et), (CN, SO2Ph), (Meldrum's type), and (SO2Ph, SO2Ph) could be used as a Michael acceptor. The present reaction provides a new method for the synthesis of tetrahydrofuran derivatives from vinylic oxiranes and Michael acceptors.
Palladium-Catalyzed Regioselective [3 + 2] Cycloaddition of Vinylic Oxiranes with Activated Olefins. A Facile Synthesis of Tetrahydrofuran Derivatives
作者:Jae-Goo Shim、Yoshinori Yamamoto
DOI:10.1021/jo972317w
日期:1998.5.1
The reaction of certain activated olefins (Michael accepters) 5 with vinylic oxiranes 1 in the presence of catalytic amounts of Pd(PPh3)(4) (5 mol %) in THF at 40 degrees C gave the corresponding [3 + 2] cycloaddition products 6. In all cases the reactions proceeded in regioselective manner, affording the corresponding polysubstituted tetrahydrofuran derivatives. The nature of electron-withdrawing group in activated olefins affected significantly the reactivity of substrates. Michael accepters having sterically less bulky electron-withdrawing groups were essential for the cycloaddition reaction, and the presence of two electron-withdrawing groups at the ct-position was needed. Accordingly, activated olefins having (CN, CN), (CN, CO2Et), (CN, SO2Ph), (Meldrum's type), and (SO2Ph, SO2Ph) could be used as a Michael acceptor. The present reaction provides a new method for the synthesis of tetrahydrofuran derivatives from vinylic oxiranes and Michael acceptors.