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Summary
Synthesis of urea compounds is highly significant for pharmaceutical chemistry, agricultural chemistry, matterials science and organic synthesis. By ultilizing ligands to switch the chemoselectivity, two transformations of vinyl cyclic carbamates and isocyanates were developed to afford linear and cyclic ureas in a controlled manner. When phosphoramidite was used as the monodentate P-ligand, a wide range of (E)-1,3-diene-substituted linear ureas were produced in high yields and selectivity (21 examples, 51%similar to 95% yields). While, using bidentate biphosphine ligand to replace the phosphoramidite ligand, a variety of highly functionalized vinyl-substitued cyclic ureas, tetrahydro-2-pyrimidinones, were delivered instead starting from the same chemical feedstocks (8 examples, 72%similar to 94% yields). To illusrate the switched chemoselectivity, two possible reaction mechanisms were proposed based on the experiment results and proceeding literatures. The keys of these two reactions, dienylation and annulation, are the ss-hydride elimination and the N-allylic alkylation of ally-Pd species, respectively. It is supposed that the basicity of the ligand will affect the reactivity of p-ally-Pd intermediates toward electrophilic ring closing. It is believed that this research not only enriches the application of vinyl carbamate reagents in organic synthesis, but also provides a new protocol to access significant nitrogen-containing molecules.
