Palladium-Catalyzed Regioselective [3 + 2] Cycloaddition of Vinylic Oxiranes with Activated Olefins. A Facile Synthesis of Tetrahydrofuran Derivatives

The reaction of certain activated olefins (Michael acceptors) 5 with vinylic oxiranes 1 in the presence of catalytic amounts of Pd(PPh 3 ) 4 (5 mol %) in THF at 40 °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 acceptors having sterically less bulky electron-withdrawing groups were essential for the cycloaddition reaction, and the presence of two electron-withdrawing groups at the α-position was needed. Accordingly, activated olefins having (CN, CN), (CN, CO 2 Et), (CN, SO 2 Ph), (Meldrum's type), and (SO 2 Ph, SO 2 Ph) 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.