Silylium ion migration dominated hydroamidation of siloxy-alkynes.

The mechanism of silver-catalyzed hydroamidation of siloxy-alkynes reaction remains controversial. Using density functional theory (DFT), we revealed that the reaction takes place through a silylium ion migration mediated hydroamination (SMH) pathway. The SMH pathway goes through two steps, the first step is Ag+ promoted proton and silylium ion exchange between siloxy-alkynes and amide, leading to ketene and silyl-imines, the second step is Ag+ catalyzed nucleophilic addition between ketene and silyl-imines, following with a silylium ion migration afford the final product. In this reaction, Ag+ activates the siloxy-alkyne into silylium ion (TIPS+) and silver-ketene through the p-π conjugate effect, the silylium ion then catalyzes the reaction. According to our calculation, the scopes of alkynes in this reaction may be extended to silyl-substituted ynamines or silyl-substituted ynamides. The scopes of amide may be extended into the p-π conjugate system such as diazoles, diazepines, etc. Our calculations also reveal a concise way to construct enamides through Ag+ catalyzed nucleophilic addition between substituted-ketenes and silyl-substituted p-π conjugate system.