Silylcuprations alkynes

Silylcupration of Alkynes. Silylcupration of alk)mes may be made catalytic in copper by treating the silyllithium reagent with methylmagnesium iodide, followed by adding a catal)hic amount of copper(I) cyanide. The regiochemistry with terminal acetylenes is unimpaired, and the intermediate vinyl copper species reacts efficiently with allyl diphenyl phosphate. 

Scheme 3.16. Silylcupration of alkynes with (t-BuPh2Si)2CuLi-LiCN and electrophilic trapping of the vinylcuprate reagent [69].

Scheme 3.18. Ring-formation by intramolecular trapping of the vinylcuprates resulting from silylcupration of alkynes with magnesium silylcuprates [75a] or lithium silylcuprates (mCPBA = m-chloroperbenzoic acid) [75bj.

Dialkyl phosphites such as 49 (Scheme 9) have been reacted as nucleophiles with activated pyridines [69, 70]. The first examples of this chemistry involved either 77-alkyl-pyridinium salts in the presence of DDQ, or pyridine and terminal alkynes as activating agents in a one-step protocol. The reaction proceeds under mild conditions that include AI2O3 catalysis. Quinolines 1 and chloroformates afford the expected adducts 68. The latter structures can be easily oxidized with O3 to provide the substituted indoles 69 (Scheme 12a). Isoquinolinephosphonates obtained this way have been used in Wittig-Homer chemistry. The whole sequence offers ready access to alkyl substituted isoquinolines [71]. Analogously, sUyl substituents have been introduced into A-acylated pyridines by using silylcuprates [72]. 

Alkynes can be transformed into alkenylstannanes by reaction with stannyl-cuprates. It is possible to trap the 1,2-dimetallic alkene species with various electrophiles. The analogous vicinal difunctionalization of alkynyl selenides " has also been reported. A route to trisubstituted alkenes from phenylthioacetylene"" starts with cuprate addition, but a 1,2-metal rearrangment is involved. Enamines are obtained from N-ethynyldiphenylamine. The alkenylcopper intermediate is also reactive toward many electrophiles. Silylcupration of functionalized alkynes may lead to cyclic products by virtue of intramolecular alkylation. ... 

PhsSiCl to give the iron silane (eq 7) Silylcuprates can be prepared by lithiation of PhsSiCl followed by treatment with cop-per(I) ion. Addition of the lithium disilylcuprate to aroyl chlorides produces the acyl silane (eq 13), while conjugate addition of the higher order silyl cyanocuprate to an alkynic morpholin-ium species was utilized for the synthesis of a heterosubstituted aUenylsilane (eq 14). ... 

Silylcupration of Alkynes. Higher-order silyl cuprates such as (1) add regioselectively to terminal alkynes in a cis fashion, and the intermediate vinylcopper species (4) may be trapped with electrophiles to give 2,2-disubstituted vinylsilanes (5) (eq 5). Corresponding reactions with the lower-order cuprate of reagent (1) give low yields of regioisomeric vinylsilanes upon protonation. ... 

Silylcupration of Alky nes. A few nonterminal unsymmetrical alkynes have been shown to undergo regioselective silylcupration. Control has been achieved by intramolecular protonation (eq 14) and by having different environments that allow diastereofacial chelation (eq 15), where the vinylsilane was subjected immediately to iododesDylation. When one side of the acetylene has a methyl group and the other a branched carbon, complete regioselectivity is achieved via attachment by the silyl group at the less hindered side. ... 

Extremely efficient and convenient ways to prepare alkenyl- and alkylsilanes are transition metal-catalyzed silylation of alkynes and alkenes respectively. A general mechanistic scheme should involve oxidative addition of Si-X (X = H, B, C, Si, Sn, S, and halgen) bonds to transition metal catalysts M followed by insertion of unsaturated bonds into either Si-M or X-M (M = transition metal) bond and reductive elimination (Scheme 3-22). On the other hand, highly reactive silylmetal reagents such as silylzincates and silylcuprates effect similar transformation without the aid of transition metal catalysts. 

Silylcuprate reagents add across alkynes without any additional transition metal-catalysts. The reaction with 1,2-dienes shows divergent regioselectivity depending on substituents on the silicon center to give either of-substituted vinylsilanes or y substituted... 

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