β-H elimination is an intrinsic problem in transition metal-catalyzed reactions.We describe herein an interesting ligand effect for Et2Zn acting as either ethyl provider or H provider,respectively:by applying SPhos o...β-H elimination is an intrinsic problem in transition metal-catalyzed reactions.We describe herein an interesting ligand effect for Et2Zn acting as either ethyl provider or H provider,respectively:by applying SPhos or Gorlos-Phos as the ligand,β-H elimination has been successfully controlled in the corresponding Negishi coupling reaction affording different poly-substituted allenes in good yields and excellent selectivities.SAESI-MS (Solvent Assisted Electrospray Ionization Mass Spectrometry) has been applied to successfully capture the highly reactive organometallic intermediates,which show the different coordination behaviors of Pd with SPhos or Gorlos-Phos as the ligand in the catalytic cycle.In addition,the different reactivities of Int 1 and Int 2 towards the formation of the final allene products have been demonstrated via SAESI-MS/MS experiments.These MS studies visualized the whole catalytic cycle for the Negishi coupling reaction while nicely explain the observed reactivity and selectivity.展开更多
Becausecarbon dioxideisabundant,cheap andnontoxic in or-ganic synthesis,much work hasbeen done in organic synthesis with carbon dioxide.[1]Allenes are an important series of com-pounds,and there arelots of reports abo...Becausecarbon dioxideisabundant,cheap andnontoxic in or-ganic synthesis,much work hasbeen done in organic synthesis with carbon dioxide.[1]Allenes are an important series of com-pounds,and there arelots of reports about synthesis of allenes or using allenes as starting materialsin recent years.[2]In our previ-ous work,we reportedthe synthesis of allenoic acids by using 2-alkynyl bromides with zinc powder under CO2atmosphere.[3]In order to synthesizeallenoic acids,at the beginning of our study,1-phenylhept-2-ynyl methyl carbonate 1aand diethyl zinc were used as the substrates for optimization of the reaction conditions under CO2atmosphere.Neither allenoic acid nor its zincate was obtained as we expected.However,a mixture of ethylation prod-uct 2aandβ-H elimination product 3awas formed instead as judged by NMR.β-H elimination is an intrinsic challenge in or-ganometallic reactions involving alkyl species.展开更多
基金Financial supports from the National Natural Science Foundation of China(Grant No.21690063)the National Basic Re1search Program(2015CB856600)are greatly appreciated.
文摘β-H elimination is an intrinsic problem in transition metal-catalyzed reactions.We describe herein an interesting ligand effect for Et2Zn acting as either ethyl provider or H provider,respectively:by applying SPhos or Gorlos-Phos as the ligand,β-H elimination has been successfully controlled in the corresponding Negishi coupling reaction affording different poly-substituted allenes in good yields and excellent selectivities.SAESI-MS (Solvent Assisted Electrospray Ionization Mass Spectrometry) has been applied to successfully capture the highly reactive organometallic intermediates,which show the different coordination behaviors of Pd with SPhos or Gorlos-Phos as the ligand in the catalytic cycle.In addition,the different reactivities of Int 1 and Int 2 towards the formation of the final allene products have been demonstrated via SAESI-MS/MS experiments.These MS studies visualized the whole catalytic cycle for the Negishi coupling reaction while nicely explain the observed reactivity and selectivity.
文摘Becausecarbon dioxideisabundant,cheap andnontoxic in or-ganic synthesis,much work hasbeen done in organic synthesis with carbon dioxide.[1]Allenes are an important series of com-pounds,and there arelots of reports about synthesis of allenes or using allenes as starting materialsin recent years.[2]In our previ-ous work,we reportedthe synthesis of allenoic acids by using 2-alkynyl bromides with zinc powder under CO2atmosphere.[3]In order to synthesizeallenoic acids,at the beginning of our study,1-phenylhept-2-ynyl methyl carbonate 1aand diethyl zinc were used as the substrates for optimization of the reaction conditions under CO2atmosphere.Neither allenoic acid nor its zincate was obtained as we expected.However,a mixture of ethylation prod-uct 2aandβ-H elimination product 3awas formed instead as judged by NMR.β-H elimination is an intrinsic challenge in or-ganometallic reactions involving alkyl species.
