Silyl-cuprate reaction

Trialkylsilyl higher-order cyanocuprates are prepared directly by trans-metallation of silylstannanes with higher-order dibutylcyanocuprates (Scheme 32) (101). In this method, steric bulkiness around silicion is essential for formation of the silylcuprates, so that the t-butyl or thexyl group is present on silicon otherwise, stannyl anion is formed. These reagents undergo typical silyl-cupration reactions, as mentioned earlier. 

Allylic phosphates and allylic phosphinates (114) have been used as electrophiles in efficient silyl cupration reactions of a variety of acetylenes. This method provides an easy access to substituted 1,4-diene systems (115) (Scheme 25). "... 

SN displacement reactions, 27-9 a-Selenocyclohexanones, 77 Senecioyl chloride, 33 Silmagnesiation, platinum-catalysed, 8 Silametallation of terminal alkynes, 7-9 Silver acetylide, 49 Silver trifluoroacctate, 42,127 Silyl cuprates, 7... 

Jin and Weinreb reported the enantioselective total synthesis of 5,11-methano-morphanthridine Amaryllidaceae alkaloids via ethynylation of a chiral aldehyde followed by allenylsilane cyclization (Scheme 4.6) [10]. Addition of ethynylmagnesium bromide to 27 produced a 2 1 mixture of (S)- and (R)-propargyl alcohols 28. Both of these isomers were separately converted into the desired same acetate 28 by acetylation or Mitsunobu inversion reaction. After the reaction of 28 with a silyl cuprate, the resulting allene 29 was then converted into (-)-coccinine 31 via an allenylsilane cyclization. 

Scheme 3.27. Regioselectivity in reactions of silyllithium and silyl cuprate reagents with allylic carbamates and epoxides...

Other addition reactions Additions involving carbon Copper(I) chloride, 85 Lithium bis(dimethylphenyl-silyl)cuprate, 161 Manganese(III) acetate, 171 Mercury(II) chloride, 175 2-(Phenylseleno)acrylonitrile, 244 Threophos, 298 Additions involving nitrogen Benzeneselenenyl halides, 26 Additions involving oxygen Bis(Tj5-cyclooctadienyl)ruthe-nium(II), 35... 

N-Phenylselenophthalimide, 245 Additions involving selenium Benzeneselenenyl halides, 26 N-Phenylselenophthalimide, 245 Miscellaneous reagents Aluminum chloride, 15 Lithium bis(dimethylphenyl-silyl)cuprate, 161 Organotin reagents, 211 Addition reactions to carbonyl... 

Anionic ring-opening polymerization of l,2,3,4-tetramethyl-l,2,3,4-tetraphenylcyclo-tetrasilane is quite effectively initiated by butyllithium or silyl potassium initiators. The process resembles the anionic polymerization of other monomers where solvent effects play an important role. In THF, the reaction takes place very rapidly but mainly cyclic live- and six-membered oligomers are formed. Polymerization is very slow in nonpolar media (toluene, benzene) however, reactions are accelerated by the addition of small amounts of THF or crown ethers. The stereochemical control leading to the formation of syndiotactic, heterotactic or isotactic polymers is poor in all cases. In order to improve the stereoselectivity of the polymerization reaction, more sluggish initiators like silyl cuprates are very effective. A possible reaction mechanism is discussed elsewhere49,52. 

As discussed, conjugate addition reactions involving chiral y-alkyl-substituted unsaturated carbonyl derivatives usually occur with low levels of diastereoselectivity. In accord with this general trend, the benzyloxy and silyloxy derivatives 103 and 104 (Scheme 6.23) both reacted with a silyl cuprate in non-selective fashion, to give the conjugate adducts 108 and 109, respectively (entries 1 and 2, Tab. 6.3) [39]. Conversely, hi levels of diastereoselectivity were found for the corresponding carbamates, and even better results were obtained for carbonates, giving the anti esters 110-112 as the major diastereomers (entries 3-5) [39]. 

Keywords Reaction Intermediates / Tris(trimethylsilyl)silyllithium / Lithium Silyl Cuprates / Disilagermirane... 

The leaving group X may be only an OH group, inserted by hydroxylation of a silyl enol ether 136 (chapter 33) formed by conjugate addition of a silyl cuprate (chapters 9 and 10) to an enone 135 and protected by the robust silyl group TBDMS (f-BuMe2Si-) 137 for reaction with the lithium derivative of 117. 

Another route to this cyclohexyl derivative involves the preparation of 6.183 via an olefmation reaction with a substituted phenylalinal derivative followed by reduction of the phenyl ring. The alcohol moiety in 6.183 was converted to the N-phthal-oyl derivative (6.184) by a Mitsunobu inversion.m Conjugate addition with a higher order silyl cuprate gave 6.185. The silyl moiety was converted to an alcohol (6.186) by treatment with tetrafluoroboric acid and then KF/m-chloroperoxy-benzoic acid. Removal of the phthalimidoyl group with hydrazine led to an amino-ester, which cyclized to lactam 5.757.11 Hydrolysis gave 4-amino-5-cyclohexyl-3-hydroxypentanoic acid (6.188) in 60% yield. 

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