Abstract
A catalytic system composed of Pd(OAc)2 and P(o-tol)3 was found to be effective for the Heck reaction of aryl bromides with diarylethylenes. Using K2CO3 as a base and DMF as a solvent, trisubstituted olefins were obtained in good to excellent yields. Aryl bromides containing an electron-withdrawing group in para position were less reactive for the Heck coupling reaction and gave substantial amount of homocoupling by-product suggesting that oxidative addition is not the rate-determining step. Electron withdrawing group substituent in the para position of stilbene affects the regioselectivity of the reaction. In this case, the phenyl group from the Ph-Pd complex migrates preferentially to the same carbon of the double bond to which the phenyl is bonded. Finally, a one pot sequential double Heck arylation of styrene was performed, giving trisubstituted olefin with an overall yield of 73%.
Highlights
Palladium-catalyzed Heck cross-coupling reactions are one of the most efficient methods for the construction of C−C bonds and have found widespread use in organic synthesis.[1]
Conversion, regio and diasteroselectivity were determined by the techniques: gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS) and 1H and 13C nuclear magnetic resonance (NMR)
The reaction mixture was stirred at 130 °C for 5 h and conversion, regio- and diasteroselectivity were determined by GC and GC-MS analysis
Summary
Palladium-catalyzed Heck cross-coupling reactions are one of the most efficient methods for the construction of C−C bonds and have found widespread use in organic synthesis.[1] Most Heck reactions involves arylation of monosubstituted alkenes (especially acrylates and styrene derivatives) to allow synthesis of disubstituted olefins with regio and stereoselective control. Stereocontrol during the synthesis of highly substituted double bonds is a significant challenge in organic synthesis,[2] and the Heck reaction remains an important alternative. In this context, some examples of regio and stereoselective syntheses of trisubstituted α,β-unsaturated compounds, such as nitriles,[3,4] cinnamates[5,6,7,8,9,10] and aldehydes,[11] through either
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