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Combining palladium and ammonium halide catalysts for Morita–Baylis–Hillman carbonates of methyl vinyl ketone: from 1,4-carbodipoles to ion pairs
Authors:Yang Yang  Bo Zhu  Lei Zhu  Ying Jiang  Chun-Ling Guo  Jing Gu  Qin Ouyang  Wei Du  Ying-Chun Chen
Institution:Key Laboratory of Drug-Targeting and Drug Delivery System of the Ministry of Education, West China School of Pharmacy, and State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu 610041 China, Fax: +86 28 85502609 ; College of Pharmacy, Third Military of Medical University, Chongqing 400038 China,
Abstract:Here we report that Morita–Baylis–Hillman carbonates from diverse aldehydes and methyl vinyl ketones can be directly utilised as palladium-trimethylenemethane 1,4-carbodipole-type precursors, and both reactivity and enantioselectivity are finely regulated by adding a chiral ammonium halide as the ion-pair catalyst. The newly assembled intermediates, proposed to contain an electronically neutral π-allylpalladium halide complex and a reactive compact ion pair, efficiently undergo asymmetric 4 + 2] annulations with diverse activated alkenes or isatins, generally with high regio-, diastereo- and enantio-selectivity, and even switchable regiodivergent or diastereodivergent annulations can be well realised by tuning the substrate or catalyst assemblies. An array of control experiments, including UV/Vis absorption study and density functional theory calculations, are conducted to rationalise this new double activation mode combining a palladium complex and an ammonium halide as an ion-pair catalyst.

A double activation catalytic system combining a palladium complex and an ammonium halide was developed to promote the asymmetric 4 + 2] annulations of Morita–Baylis–Hillman carbonates of methyl vinyl ketone.
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