Silylcuprates substitution reactions

Like their carbon counterparts, silylcuprates and stannylcuprates readily participate in SN2 -substitution reaction with allylic electrophiles.43,51 For example, <37z//-diastereoselective allylic substitution of the vinyl oxiranes 147 with the lower-order cyanocuprate (PhMe2Si)Cu(CN)Li cleanly affords the allylsilanes 148 (Scheme 38).106 Products of this type can be converted into the corresponding diols with retention of configuration by Tamao-Fleming oxidation 53,53a,53b,107... 

Allylsilanes in which the silyl group is at the more substituted end of the allyl system have been prepared by a reaction sequence involving the conjugate addition of silylcuprates to a, jS-unsat-urated esters followed by reduction and dehydration via selenoxide elimination38. 

Silylcuprates have been reported to undergo reactions with a number of miscellaneous Michael acceptors [65]. Conjugate addition to 3-carbomethoxy acyl pyri-dinium salts [65a] affords 4-silyl-l,4-dihydropyridines. Oxidation with p-chlorand generates a 4-acyl pyridinium salt that gives the 4-silylnicotinate upon quenching with water, and methyl 4-silyl-2-substituted dihydronicotinates upon quenching with nucleophiles (nucleophilic addition at the 6-position). The stabilized anion formed by conjugate addition to an a, j8-unsaturated sulfone could be trapped intramolecularly by an alkyl chloride [65b]. 

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]. 

Silylcupration of allene with (PhMe2Si)2CuLi followed by treatment of the intermediate cuprate with H" ", carbon electrophiles, and CI2 affords the corresponding vinylsilanes (eq 9). However, reaction of the intermediate cuprate with I2 affords an allylsilane, from which other more highly substituted allylsilanes are readily obtainable (eq 9). In reaction with substituted allenes, the product ratio (vinylsilane vs. allylsilane) is dependent upon the degree of substitution. ... 

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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