- A new regio- and stereoselective intermolecular Friedel-Crafts alkylation of phenolic substrates with aryl epoxides
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A conceptually new regioselective and highly syn-stereoselective intermolecular Friedel-Crafts-type O-alkylation of phenols with aryl epoxides by the use of appropriately substituted aryl borates is reported. The carbon-carbon bond formation occurs in neutral and mild conditions without the need for external Lewis acids or transition metal catalysts.
- Bertolini, Ferruccio,Crotti, Paolo,Macchia, Franco,Pineschi, Mauro
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- Catalytic hydrocyanation of olefins by nickel(0) phosphite complexes - Effects of Lewis acids
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Mechanistic studies on the addition of HCN to olefins using Ni[P(O-o-tolyl)3]3 catalyst show that the reactions proceed under mild conditions via (η1-organo)- or (η3-organo)nickel cyanide intermediates formed by the insertion of monoenes or dienes into the nickel-hydrogen bond of HNiL3CN. The RNiLmCN intermediates can be identified spectroscopically by NMR and IR in some cases. In the case of very electronegative R groups (formed for example from reactions of HNiL3CN with C2F4 or acrylonitrile), reductive elimination does not occur, and the catalyst is poisoned for olefin hydrocyanation. Improved rates, catalyst lifetimes, and product linearity can be obtained by the addition of Lewis acid (A) cocatalysts. Spectroscopic studies show that Lewis acids can coordinate strongly to the nitrogen lone-electron pair of hydrido cyanide intermediates to form HNiL3CN-A complexes. An explanation of the effects of Lewis acids on hydrocyanation is proposed, which involves increasing the concentration of nickel in catalytic loop species [in the P(O-p-tolyl)3 system], accelerating the rate of carbon-carbon coup ing to form alkanenitriles from alkylnickel cyanide complexes and destabilizing relatively bulky branched alkyl intermediates relative to less crowded linear ones.
- Tolman,Seidel,Druliner,Domaille
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