Dual Palladium/Copper-Catalyzed anti-Selective Intermolecular Allenylsilylation of Terminal Alkynes: Entry to (E)-Silyl Enallenes

Abstract

A palladium-/copper-cocatalyzed three-component trans-allenylsilylation of terminal alkynes with propargyl acetates and PhMe 2 SiBpin is described, which is driven by the regioselective allenylation of the alkyne with propargyl acetates and then silylation. This method allows the simultaneous incorporation of an allene and silicon across the CC bond and provides a highly chemo-, regio-, and stereoselective alkyne difunctionalization route to the synthesis of valuable (E)-silyl enallenes. The utility of this method is highlighted by late-stage derivatization of bioactive compounds.

Nickel-Catalyzed Reductive Cross-Coupling of Propargylic Acetates with Chloro(vinyl)silanes: Access to Silylallenes

“…To elucidate the mechanism for this nickel-catalyzed reductive cross-coupling protocol, control experiments were conducted (Scheme ). Under optimal conditions, treatment of propargyl acetate 1a with chlorosilane 2a and D 2 O afforded the deuterium-labeled allene 4a- d1 , no target product 3aa , in 56% yield (eq 1), while the reaction of propargyl acetate 1a with silane 2a and H 2 O efficiently executed and delivered allene 4a in 78% yield (run 1; eq 2). , Notably, without silane 2a , propargyl acetate 1a reacted with H 2 O, (Ph 3 P) 2 NiBr 2 , L1 , and Zn furnished allene 4a exclusively in 81% yield (run 2; eq 2). While in the absence of both chlorosilanes and H 2 O, the reaction of propargyl acetate 1a afforded only 4a in only 40% yield due to H 2 O presented in DMF and the reaction system (run 3; eq 2), no reaction of propargyl acetate 1a under anhydrous conditions (dry DMF) was observed (run 4; eq 2).…”

“…The working mechanisms for this Ni-catalyzed reductive cross-coupling protocol are proposed on the basis of the current results and precedent literature studies (Scheme ). − Chlorosilane 2a may be converted to the Si-centered radical intermediate A with the aid of the active Ni 0 L n species and Zn reductant, followed by oxidative addition with the active Ni 0 L n species to form the Si–Ni I L n complex intermediate B . − Coordination and decarboxylation of the intermediate B affords the Si–Ni III (allenyl)-OAc intermediate D . Reductive elimination of the intermediate D delivers the desired product 3 and the Ni I L n OAc intermediate E .…”

“…Accordingly, the development of efficient synthetic methodologies to access these functionalized organosilanes has drawn much ongoing interest. Among them, transition-metal-catalyzed C–Si bond construction reactions play an important role in such silyl compound preparation by incorporation of the silyl functionalities and have been well investigated in recent years. , Despite extensively documented methods for the C–Si bond formation, reports of handling the transition-metal-catalyzed silylation of alkynes via the C­(sp 2 )–Si bond construction to access silylallenes remain rare. , Pioneering work on transition-metal-catalyzed hydrosilylation of 1,3-diynes with trichlorosilane to prepare trichlorosilyl allenes has been reported by Hiyama and co-workers . However, the method suffers from both a narrow scope of 1,3-diynes and limited resulting silylallenes.…”

Recent advances in carbosilylation of alkenes and alkynes

“…A three-component palladium/copper-catalyzed trans -allenylsilylation of terminal alkynes with propargyl acetates and Me 2 PhSiBpin was described by Wang & Li et al 78 in the year 2021. This was achieved through regioselective allenylation of the alkyne with propargyl acetate and subsequent silylation.…”

Recent Advances in the Functionalization of Terminal and Internal Alkynes

“…In 2021, Heng Li group developed regioselective allenylsilylation of terminal alkynes using palladium and copper dual catalyzed three component reaction of terminal alkynes, propargyl acetates and PhMe 2 SiBpin, which enable the synthesis of ( E )‐1‐silyl‐2‐allenyl alkenes (Scheme 32). [32] In this protocol, authors employed propargyl acetates as allene precursors to enable allenylation with alkynes prior to silylation. Notably, the desired vinyl silane products were obtained with excellent regio‐/stereoselectivity and functional group tolerance.…”