本帖最后由 1286488053 于 2016-8-11 17:12 编辑 |
On the basis of the above results, a plausible mechanism was proposed (Scheme 3). Initially, the alkyne is activated by cationic gold(I) generated in situ from the gold catalyst and silver salt. Subsequent nucleophilic attack of TMSN3 on intermediate A led to alkenyl azide B. Further protonation of B generated azide cation intermediate C, which could be transformed to intermediate D through an acid-catalyzed rearrangement process. Next, cation D was attacked by TMSN3 once again, producing imino azide E. The nucleophilic attack of water was prevented in this step probably owing to the protonation of H2O to H3O+ by strong or super acids. The subsequent protonation of E took place in the presence of sulfuric acid to form a-amino azide carbocation F,which would be converted to G or carbodiimide H by rearrangement and loss of a proton. Finally, nucleophilic attack by H3O+ led to the desired carbamide product 2 through the tautomerization of the intermediate I. Alternatively, 1,3-dipolar cycloaddition with azide led to the desired amino tetrazole product 3.