Allyltin compounds coupling reactions

Allyl silanes react with epoxides, in the presence of Bp3-OEt2 to give 2-allyl alcohols. The reaction of a-bromo lactones and CH2=CHCH2Si SiMe3)3 and AIBN leads to the a-allyl lactone. " Benzyl silanes coupled with allyl silanes to give ArCH2—R derivatives in the presence of VO(OEt)Cl2 " and allyltin compounds couple with allyl silanes in the presence of SnCU. " Allyl silanes couple to the a-carbon of amines under photolysis conditions. ... 

Free-radical-mediated four-component coupling reactions are rare. However, when an allyltin-mediated radical carbonylation is conducted in the presence of electron-deficient alkenes, four-component coupling reactions take place efficiently to give good yields of p-functionalized <5,fi-unsaturated ketones [40]. The wide scope of this four-component coupling reaction is noteworthy Primary, secondary, and tertiary alkyl bromides and iodides can be used as well as aromatic and vinylic halides. A variety of electron-deficient alkenes, such as methyl vinyl ketone, ethyl acrylate, acrolein, acrylonitrile, and vinyl sulfone, can be used as the acyl radical trap (Scheme 6.23). Fluorous allyltin compounds can also be used in four-component coupling reactions [41]. 

Unsaturated ketones can be readily synthesized by a three-component coupling reaction, comprised of alkyl halides, CO, and allyltin reagents [53]. Because of the slow direct addition of alkyl radicals to allyltin compounds [54], radical carbonylation with allyltin can be conducted at relatively low CO pressures to give good yields of y ,y-unsaturated ketones (Scheme 4-29). 

Later, some Japanese synthetic rubber scientists believed the attachment involved quinone groups that are on the surface of highly reinforcing blacks blocks. This was based on the work done with allyltin compounds, and was later shown to involve a concerted reaction of the allyltin end with an or /z6>-quinone structure that is present on the reactive Tin-coupled diene... 

Allyltin compounds behave as excellent unimolecular chain transfer (UMCT) reagents [49] which serve as radical acceptors and sources of tin mediators [50]. Since acyl radicals are nucleophilic radicals, the addition reaction to allyltin, which is regarded as an electron rich alkene, is not a rapid process. Ryu, Sonoda, and coworkers found that unsaturated ketones can be synthesized by a three-component coupling reaction, comprised of alkyl halides, CO, and allyltin reagents [51]. Because of the slow direct addition of alkyl radicals to allyltin compounds [50b], radical car-bonylations with allyltin can be conducted at relatively low CO pressures, and high substrate concentrations (0.1-0.05 M) were used to ensure the chain length. 

The radical carbonylation of an alkyl iodide in the presence of Kim s sulfonyl oxime ethers [58, 59, 60] provides a new type of multicomponent coupling reaction where plural radical Cl synthons are consecutively combined [61]. In the transformation, allyltin was used to serve as a trap of benzenesulfonyl radical which converts sulfonyl radical to a tin radical, thus creating a chain. Scheme 14 illustrates such an example, where the product was easily dehydroxylated to give the corresponding tricarbonyl compound on treatment with zinc/AcOH. The radical acylation reaction by Kim s sulfonyl oxime ethers can be conducted under irradiation with the addition of hexamethylditin. This is an alternative path for achieving a similar transformation without the use of photolysis equipment. Scheme 15 illustrates several examples where carbon monoxide and Kim s sulfonyl oxime ethers are successfully combined to create new tandem radical reaction sequences [61],... 

In Section 12.7.B, the Stille coupling reaction reacted a vinyl tin compound with a vinyl triflate, in the presence of palladium(O). Tetravalent tin complexes add to aldehydes and ketones, in the presence of a Lewis acid. Allyltin complexes are, by far, the most widely used of these compounds.297 a typical example is taken from the work of Keck, in which a chiral aldehyde (455) was treated with allyltributyltin, in the presence of various Lewis acids. S As shown in Table 12.19, a mixture of syn (456) and anti (457) products was obtained. The ratio of 456/457 was dependent on the structure of the R group in 455, the solvent and the Lewis acid.The anti product (457) was obtained by using the tert-butyldimethylsilyloxy derivative (sec. 7.3.A.i) of 455 with 2 equivalents of boron trifluoride in dichloromethane. The syn product is obtained preferentially when the benzyloxy derivative of 455 is used with titanium tetrachloride in dichloromethane.298... 

The same strategy was applied to radical cabonylation with fluorous allyltin reagents. Propylene-spaced fluorous allyltin reagents 22 were tested as mediators for radical carbonylations the four-components coupling reaction with RX, CO, alkenes and the fluorous allyltin produced the -functionalized i8-aUylated ketones 23 (Scheme 28). Diphasic workup (acetonitrile and FC-72) was successfully carried out to separate the products from the tin compounds. Comparison experiments... 

In basic aqueous media, a kinetic study of the reaction between stannate(II) ions and alkyl halide shows that mono- and disubstituted organotin compounds are formed (Eq. 6.12a).27 The monosubstituted organotin compound is obtained after a nucleophilic substitution catalyzed by a complexation between the tin(II) and the halide atom. The disubstituted compound results from an electrophilic substitution coupled with a redox reaction on a complex between the monosubstituted organotin compound and the stannate(II) ion. Stannate(IV) ions prevent the synthesis of the disubstituted compound by complexation. Similarly, when allyl bromide and tin were stirred in D2O at 60° C, allyltin(II) bromide was formed first. This was followed by further reaction with another molecule of allyl bromide to give diallyltin(IV) dibromide (Eq. 6.12b).28... 

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