We evaluate the author proposed NUA mechanism (Figure ). At beginning of the reaction, coordination of siloxy-alkynes 1a with the AgNTf2 is exergonic by 10.1kcal/mol (Figure ). AgNTf2 coordinate with triple bond of 1a, makes 1a susceptible to nucleophilic attack. There are three possible sites to attack 1a, which is α-C, β-C (Figure ) and silicon atom. As for the nucleophilic attack of the two sp-hybridized carbon atoms, nucleophilic at α-C position is much more facile due to p-π conjugate effect . So, we only consider nucleophilic attack of the α-C position. There are two directions of nucleophilic attack at α-C position, if nucleophilic attack take place at the AgNTf2 side, cis-addition product Z-3a will be obtained; otherwise, trans-addition product E-3a will be formed. Our calculation shows that the nucleophilic attack of 2a prefers take place at opposite side of AgNTf2 which lead to trans-conformation product E-3a, the main cause of the trans-selectivity is the trans-β effect . The C-N formation leading to Z-3a is energetically highly disfavored with a barrier (Z-TSa) 35.8kcal/mol, implies that the commonly accepted NUA pathway is disfavored.