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Stannane, transmetallation

Chiral organolead compounds 19 can be obtained, with retention of configuration, from the corresponding a-alkoxy stannanes via tin/lilhium exchange and transmetalation with bro-mo(tributyl)lcad12. [Pg.124]

Transmetalation of the appropriate allyl(tributyl)- or allyl(triphenyl)stannanes with butyllithi-um or phenyllithium offers a convenient and clean access to 2-propenyllithium 25,26,27. [Pg.233]

Two approaches for the synthesis of allyl(alkyl)- and allyl(aryl)tin halides are thermolysis of halo(alkyl)tin ethers derived from tertiary homoallylic alcohols, and transmetalation of other allylstannanes. For example, dibutyl(-2-propenyl)tin chloride has been prepared by healing dibutyl(di-2-propenyl)stannane with dibutyltin dichloride42, and by thermolysis of mixtures of 2,3-dimethyl-5-hexen-3-ol or 2-methyl-4-penten-2-ol and tetrabutyl-l,3-dichlorodistannox-ane39. Alternatively dibutyltin dichloride and (dibutyl)(dimethoxy)tin were mixed to provide (dibutyl)(methoxy)tin chloride which was heated with 2,2,3-trimethyl-5-hexen-3-ol40. [Pg.365]

Both allylstannane transmetalation and thermolysis of homoallyl stannoxanes have been used to prepare 2-butenyltin halides as (E)j(Z) mixtures44-45. The reaction between 2-butenyl-(tributyl)stannane and dibutyltin dichloride initially provides dibutyl(l-methyl-2-propenyl)tin chloride as the kinetic product by an SE2 process, but this isomerizes under the reaction conditions to give a mixture containing the (Z)- and (E)-2-butenyl isomers46. [Pg.366]

Lewis acids, particularly the boron trifluroride diethyl ether complex, are used to promote the reaction between allyl(trialkyl)- and allyl(triaryl)stannanes and aldehydes and ketones52-54. The mechanism of these Lewis acid promoted reactions may involve coordination of the Lewis acid to the carbonyl compound so increasing its reactivity towards nucleophilic attack, or in situ transmetalation of the allyl(trialkyl)stannane by the Lewis acid to generate a more reactive allylmetal reagent. Which pathway operates in any particular case depends on the order of mixing of the reagents, the Lewis acid, temperature, solvent etc.55- 58. [Pg.366]

Transmetalation to give l-methyl-2-propenylaluminum followed by isomerization to 2-butenyl isomers may be involved in reactions between aldehydes and 2-butenyl(tributyl)-stannane induced by aluminum(III) chloride in the presence of one mole equivalent of 2-propanol. Benzaldehyde and reactive, unhindered, aliphatic aldehydes give rise to the formation of linear homoallyl alcohols, whereas branched products are obtained with less reactive, more hindered, aldehydes66,79. [Pg.373]

The problem can be solved by the transformation of the lithium carbanions into the more reactive trichlorotitanium intermediates via the stannanes. Finally, the (- )-sparteine complex of (5)-( )-l-methyl-2-butenyl diisopropylcarbamate105 (Section 1.3.3.3.1.2.) is apparently transmetalated by tetraisopropoxytitanium with inversion of configuration, leading to homoaldol products with moderate diastereomeric excess103. [Pg.421]

Stannane 6a underwent facile transmetalation in tetrahydrofuran at — 78 °C on treatment with butyllithium to afford 6b. Addition of the lithium reagent 6b to a solution of 1.1 equivalents of copper(I) bromide-dimethyl sulfide in 1 1 diisopropyl sulfide/tetrahydrofuran at — 78 °C gave the copper reagent 6c, which reacted with methyl vinyl ketone at —78 "C in the presence of boron trifluoride-diethyl ether65, producing 7 in 55% yield65. [Pg.914]

To examine whether the breakdown in equilibration arose from a slow rate of equilibration or if the equilibrium does not favor the equatorial alkyllithium,the time course of equilibration was investigated (Scheme 34). The diastereomeri-cally pure a-alkoxystannanes 198 were prepared in analogy to Linderman s procedures 170], and their equilibrations were examined. Transmetallation and alkylation under kinetic control (entries 1 and 2) provided the expected equatorial and axial adducts, respectively, with no detectable minor isomer. Attempted equilibrations of the axial stannanes (entries 4 and 6) led to mixtures of axial and equatorial products. The equatorial stannane gave only the equatorial adduct under both equilibration conditions (entries 3 and 5). From these data, the authors concluded that the equilibration does take place under these conditions, and that the equilibrium lies essentially completely toward the equatorial alkyllithium. The observed product ratios in entries 4 and 6 can be attributed to a slow rate of equilibration. [Pg.85]

The allenic stannanes can be transmetallated by treatment with SnCl4, a reaction that results in the formation of the a propargyl stannane. If the transmetallation reaction is allowed to equilibrate at 0°C, an allenic structure is formed. These reagents add stereospecifically to the aldehyde through cyclic TSs.194... [Pg.851]

Certain S- and e-oxygenated allylic stannanes have been found to transmetallate with SnCU to give chiral pentacoordinated chloro stannane intermediates which add stereos-electively to aldehydes (Scheme 31)74. These reactions proceed with net 1,5-and 1,6-asymmetric induction. [Pg.235]

An alternative route to allenyl stannanes involves organocuprate displacements on propargylic chlorides bearing an alkynyl PhsSn substituent (equation 39)79. Interestingly, transmetallation by attack of the cuprate on the tin substituent is not observed in these systems. A parallel strategy can be employed for allenylgermanes (equation 39)79. The... [Pg.237]

As well as alkenylstannanes [106-108], other classes such as a-heteroatom-substituted alkyltributylstannanes [109] and, more importantly, allylic stannanes [110, 111] also undergo these Sn-Cu transmetalations. Otherwise difficult to prepare, allylic copper reagents may, however, be obtained by treatment of allylic stannanes (produced in turn from organolithium, magnesium, or zinc organometallics) with Me2CuLi LiCN. They enter into cross-coupling reactions with alkyl bromides [110] or vinyl triflates (Scheme 2.52) [111]. [Pg.68]

It has been found that enantio-enriched a-(homoallyloxy)alkyllithiums (84), formed from the corresponding stannanes (83) by stereoretentive transmetallation, cyclize with complete retention of configuration at the lithium-bearing -carbon to yield enantio-enriched Q ,jS-disubsfituted tetrahydrofurans (85 and 86). This is consistent with earlier theoretical calculations which suggested that the lithium might coordinate with the olefinic bond in the transition state. [Pg.369]

In 1991, Kessar and coworkers demonstrated that the kinetic barrier could be lowered by complexing the tertiary amine with BF3, snch that i-BuLi is able to deprotonate the ammoninm compound, which can be added to aldehydes and ketones as shown by the example in Scheme 4a. Note the selectivity of deprotonation over vinyl and allyl sites. A limitation of this methodology is that the ylide intermediate does not react well with alkyl hahde electrophiles. To get aronnd this, a seqnence that begins with the stannylation and decomplexation shown in Scheme 4b was developed. The stannane can be isolated in 94% yield (Scheme 4b) and snbseqnently snbjected to tin-lithium exchange to afford an unstabilized lithiomethylpiperidine that is a very good nucleophile. However, isolation of the stannane is not necessary and a procedure was devised in which the amine is activated with BF3, deprotonated, stannylated, decomplexed from BF3 with CsF, transmetalated back to lithium and alkylated, all in one pot (Scheme 4c). ... [Pg.1007]

The availabihty of enantioenriched 2-tribntylstannylpyrrolidines ° can be used to advantage in these reactions. Conversion to a snbstrate snitable for cyclization allows, after transmetalation, the determination of the stereoselectivity on intramolecnlar carbolithia-tion. Treatment of the enantioenriched stannane shown in Scheme 23 with bntyllithinm resnlted in the formation of the pyrrolizidine alkaloid psendoheliotridane. The prodnct was formed as a single diastereomer and with no loss of optical pnrity, occnrring with overall retention of confignration at the carbanion center. Related cychzation reactions... [Pg.1017]

As indicated in Section ni.B, deprotonation of a carbamate affords a dipole-stabilized a-amino-organolithium that can be transmetalated with copper salts to form cuprates, thereby expanding the versatility of the organolithium. Suitable electrophiles include enones, alkenyl, alkynyl, allenyl and dienyl carboxylic acid derivatives, nitriles and sulfoxides. Dieter and coworkers have shown that the same process can be accomplished via transmetalation of a stannane (Scheme 36). The procedure is particularly... [Pg.1025]


See other pages where Stannane, transmetallation is mentioned: [Pg.214]    [Pg.214]    [Pg.238]    [Pg.92]    [Pg.113]    [Pg.373]    [Pg.373]    [Pg.160]    [Pg.82]    [Pg.90]    [Pg.73]    [Pg.419]    [Pg.329]    [Pg.555]    [Pg.217]    [Pg.234]    [Pg.110]    [Pg.111]    [Pg.113]    [Pg.110]    [Pg.111]    [Pg.113]    [Pg.1002]    [Pg.1002]    [Pg.1004]    [Pg.1006]    [Pg.1009]    [Pg.1012]    [Pg.1017]    [Pg.1045]    [Pg.1089]    [Pg.547]   
See also in sourсe #XX -- [ Pg.546 ]

See also in sourсe #XX -- [ Pg.546 ]

See also in sourсe #XX -- [ Pg.346 ]

See also in sourсe #XX -- [ Pg.546 ]

See also in sourсe #XX -- [ Pg.346 ]




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