Copper-Catalyzed Cyclization of N-Propargyl Ynamides with Borane Adducts through B–H Bond Insertion

Abstract

An efficient copper-catalyzed cyclization of N-propargyl ynamides with borane adducts through B–H bond insertion has been developed. A series of valuable organoboron compounds are constructed in generally good yields with a wide substrate scope and good functional group tolerance under mild reaction conditions. Importantly, this protocol via vinyl cation intermediates constitutes a novel way of B–H bond insertion.

Copper-Catalyzed Si–H Bond Insertion Reaction of N-Propargyl Ynamides with Hydrosilanes

“…It is noteworthy that the electronic property of R had a significant effect on the reaction’s efficiency. The reaction time was substantially prolonged when there was no electron-donating group on the phenyl ring (entry 6), which is similar to our previous protocols . With respect to 3-methoxylphenyl- and piperonyl-substituted N -propargyl ynamides, the desired products 2k and 2l were obtained in 38% and 74% yields, respectively (entries 11 and 12).…”

“…In recent years, the chemistry of vinyl cations has attracted significant attention due to their unique carbene-like reactivity . During our recent studies on the copper-catalyzed diyne cyclization, , we very recently disclosed a novel copper-catalyzed enantioselective cyclization of alkenyl diynes involving a vinylic C­(sp 2 )–H functionalization, which led to a diverse array of chiral dicyclic and polycyclic pyrroles in high yields with excellent enantioselectivities . Notably, detailed mechanistic studies revealed that the reaction proceeded through key vinyl cation intermediates, and a formal carbene insertion into vinylic C­(sp 2 )–H bonds was involved in this alkenyl diyne cyclization.…”

“…Based on our previous study on the copper-catalyzed cyclization of N -propargyl ynamides and deuterium labeling experiments, , a plausible reaction mechanism to rationalize the synthesis of 4-silyl-substituted pyrrole 2a is illustrated in Scheme . Initially, catalytic Cu­(I) species coordinate with the electron-richer amide-tethered CC bond of 1a , forming the precursor A , which undergoes subsequent nucleophilic attack by another C–C triple bond to produce the key vinyl cation intermediate B .…”

Efficient access to 1,3,4-trisubstituted pyrroles via gold-catalysed cycloisomerization of 1,5-diynes

“…20 The subsequent 5- endo-dig cyclization reaction occurs to form a highly reactive vinyl cationic intermediate B . 13 m ,14,15,21 Nucleophilic addition of B with an external H 2 O nucleophile generates intermediate C , and C can isomerize to D . Protodeauration of D and subsequent autooxidation would eventually produce pyrrole 2a .…”

Rhodium-Catalyzed Intramolecular Cyclization to Synthesize 2-Aminobenzofurans via Carbene Metathesis Reactions

“…However, there are still some unknowns about the carbon–sulfur bond insertion. Given that the donor carbene and donor–donor carbene have a higher reactivity than the acceptor carbene, the synthesis of the donor carbene precursor is somewhat difficult and it is often generated in situ, which could be easily captured by the nucleophiles in the system.…”