Rare-Earth Silylamide-Catalyzed Monocoupling Reaction of Isocyanides with Terminal Alkynes

[reaction: see text] Rare-earth silylamides, Ln[N(SiMe3)2]3 (Ln = Y, La, Sm, Yb), serve as good catalysts for monoinsertion of isocyanides into terminal alkynes in the presence of amine additives, leading to 1-aza-1,3-enyens in excellent yields. The reaction is applicable to a diverse set of terminal alkynes with various functionalities such as ethers, acetals, and amino groups. Larger metals (La and Sm) give a better performance than smaller ones (Y and Yb). Using less hindered primary amines and, in contrast, bulky isocyanides is crucial for the coupling reaction; otherwise, competitive oligomerization of the isocyanides occurs predominantly. In the mechanistic study, the rate-determining step of the reaction seems to be the first insertion of the isocyanides into rare-earth alkynides, which is followed by spontaneous protonation with the amine additives.