Allyltin reagents

Alkynes react with indium reagents such as (allyl)3ln2l3 to form dienes (allyl substituted alkenes from the alkyne). Allyltin reagents add to alkynes in a similar manner in the presence of ZrCU Alkylzinc reagents add to alkynes to give substituted alkenes in the presence of a palladium catalyst. ... 

Later, Torii et al. found that the tin-aluminum-mediated allylation can be carried out with the less expensive allyl chloride, instead of allyl bromide, when a mixture of alcohol-water-acetic acid was used as the solvent.77 When combined with stoichiometric amounts of aluminum powder, both stoichiometric and catalytic amounts of tin are effective. As reported by Wu et al., higher temperatures can be used instead of aluminum powder.78 Under such a reaction condition, allyl quinones were obtained from 1,4-quinones, followed by oxidation with ferric chloride. Allylation reactions in water/organic solvent mixtures were also carried out electrochemically, with the advantage that the allyltin reagent could be recycled.79... 

Formation of a bis-allylated product of 4-nitrobenzoyl chloride by the reaction with allyltrimethyltin in the presence of a benzylpalladium(ll) complex was observed by Stille and co-workers in 1983.4 Trost and King also reported allylation of aldehydes by allyltin reagents in 1990.456 However, the precise mechanism was unclear until the extended studies were performed by Yamamoto and co-workers since 1995.4S7,4S7a 4S7 Aldehydes and imines react with allyltin reagents in the presence of a palladium catalyst (Equations (95) and (96)), and imines are chemoselectively allylated in the presence of aldehydes (Equation (97)).4S7,4S7l 4 b Mechanistic studies using NMR spectroscopy proved that bis-7t-allylpalladium complex 203 is a key nucleophilic intermediate (Figure 3). 

Platinum-catalyzed allylation of aldehydes with allyltin reagents was first reported in 1995.4S7 457b,483 483a Ar0matiC) aliphatic, a,/3-unsaturated aldehydes and even cyclohexanone undergo allylation with allyltributyltins in the presence of PtClgtPP 113)2 >n THF at room temperature or higher temperature (Equations (123) and (124)). Allylplatinum species are considered to be the active intermediates on the basis of related mechanistic studies on palladium catalysis. 

Alkoxides that arise from simple carbonyl additions have also functioned as excellent in situ nucleophiles for intramolecular hydroalkoxylation reactions. Garbinols derived from the addition of allyltin reagents have proved to be potent nucleophiles in reactions of this type (Equation (99)),349 and this approach has also been used for the combined addition-cyclization of alkynals under Pd(n)350 or Cu(i)351 catalysis, and alkynones under Pd(n) catalysis.352... 

Recently, the electrochemical recycKng of allyltin reagents has been realized for the first time in protic solvents. Difhculties in the recycling of metallic allyl reagents in situ are due to the fact that reaction conditions that allow... 

Stereoselective addition of allyl metal reagents to various functionalities is an important reaction in organic synthesis [32, 33]. The allylation of epoxides and aziridines with allyltin reagent is catalyzed by Lewis acids. Even though many Lewis acids have been reported to catalyze this reaction, Bi(OTf)3 is distinct because it avoids the formation of byproducts and is also environmentally more compatible. It catalyzes the reaction of aryl epoxides with tetraallyltin to afford the corresponding homoallyllic alcohol [34]. 

The mechanism of coupling of allyltin and allylpalladium can be altered by the addition of maleic anhydride to the reaction mixture (vide infra).m In this modified procedure, reaction of the allylpalladium chloride dimer with allyl-Bun3Sn now gives coupling without allyl inversion of the allyltin reagent. 

Allyltin reagents were suggested to add to ir-allylpalladium complexes directly on the allyl ligand,137138 although a definitive stereochemical experiment could not be successfully carried out. The fact that these reactions proceed with allyl inversion of the stannane (equation 168) would require an unlikely, sterically unfavorable allylpalladium-R intermediate if metal attack was followed. 

However, the reaction of preformed allylpalladium complexes with allyltin reagents with coadded maleic anhydride does proceed via metal addition (equation 169).139... 

Allylation of quinones,1 This reaction has been effected with allylsilanes mediated by TiCLt, but allyltin reagents activated by BF3 etherate are now preferred. The allylated hydroquinones can be oxidized to quinones directly by FeCl3. 

The reaction of a-ethoxy carbamates and BF3 etherate or TiCl4 (1 equiv.) with ay-alkoxy allyltin reagent results in 1,2-amino alcohols with moderate to high syn-... 

Under thermodynamic control, the homoallylic alcohol is obtained with an anti/syn selectivity up to 95 531-33. In order to prevent competition between the transmetallation and the complexation of the aldehyde, it is important that the allyltin reagent is added first to the Lewis acid. This is termed a reverse addition . 

The allylation of carbonyl compounds with allyltin reagents is still an active area of organotin chemistry from the methodological point of view, and also for synthetic applications. For completeness we should add several alternative techniques, such as the development of trifluoromethanesulphonic acid as a Bronsted acid catalyst for the allylation of aldehydes in water123, or the design of fluorous allyltin reagents for the platinum-catalysed allylation of aldehydes124. 

Allyltin reagents supported on polymer underwent free radical allylic transfer with a marked preference for electron-poor carbon radicals598. The fluorous method developed by Curran and coworkers has recently been successfully extended to four-component radical reactions using fluorinated allyltin reagents599. 

The radical chemistry of organotins is undoubtedly dominated by tin hydride chemistry, which has been at the source of radical chain reactions of valuable interest for organic synthesis. However, the demonstration of the ability of allyltin reagents to undergo homolytic cleavage of the carbon-tin bond goes back to the early and only ten years... 

The initiation step (i) producing the tributyltin radical can be performed by thermolysis of radical initiators such as AIBN. Complementarily, the use of a Et3B/02 system or of photochemical irradiation allows the reactions to proceed at low temperature. The reaction (ii) with the substrate forming the carbon radical applies the same substrates as those used in tin hydride chemistry, such as iodides, bromides, selenides xanthates and even thiocarbonates. Furthermore, the possible competitive addition of tributyltin radicals to the allyltin reagent is of no consequence due to the rapid /3-fragmentation of the resulting carbon-centred radical, which renders this reaction a degenerate one. It is noteworthy that less reactive radical precursors such as chlorides or phenyl thioethers can be used efficiently. The evolution of the radical (iii) via several intra- or intermolecular elementary... 

---