Tetraallyltin

The allyltin halides can then be obtained by a disproportionation reaction between tetraallyltin and tin tetrachloride or tetrabromide, a reaction that is exothermic (143,144). 

Tetraallyltin is more reactive than tetravihyltin, but, with methanol as the solvent, acidolysis can be restricted to the stage of the formation of the triallyltin or diallyltin carboxylates (186). 

Allylation of the nitro group on nitrobenzene derivatives proceeded under similar reaction conditions (Eq. 11.36).64 Allylation reactions of various benzoylhydrazones with tetraallyltin were carried out in... 

During our investigations of the reactions mediated by LASCs, we have found that addition of a small amount of a Bronsted acid dramatically increased the rate of the aldol reaction (Eq. 5).[191 This cooperative effect of a LASC and an added Bronsted acid was also observed in the allylation ofbenzalde-hyde with tetraallyltin in water.1201 Although, from a mechanistic point of view, little is known about the real catalytic function of scandium and proton, this cooperative effect of a Lewis acid and a Bronsted acid provides a new methodology for efficient catalytic systems in synthetic chemistry. 

By treating Nafion (NR-50), a perfluorinated acidic ion exchanger based on sulfonic acid groups, with scandium(III) chloride hexahydrate Kobayashi et al. generated a solid scandium-derived catalyst (29) (Nafion-Sc) that proved to be effective in al-lylation reactions of carbonyl compounds with tetraallyltin (Scheme 4.15). Since the catalyst is stable in both organic solvents and water, even unprotected carbohydrates could be transformed directly in aqueous solvents. The resulting homo-allylic alcohols were separated by simple filtration [97]. 

A modified rare earth catalyst (30) which is based on a polystyrene backbone as depicted in Scheme 4.15 can be applied even in neat water. It is attached via a hydrophobic oligomeric linker which creates a nonpolar reaction environment and acts as a surfactant for the substrates. The reaction of 4-phenyl-2-butanone with tetraallyltin in water using 1.6 mol% of the scandium catalyst (30) afforded the corresponding homoallylalcohol in a yield of 95%. Interestingly, when using other solvents (dichloromethane, acetonitrile, benzene, ethanol, DMF) the yields decreased drastically, indicating a much higher reaction rate in water [98]. 

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]. 

Reaction of styrene oxide with tetraallyltin in the presence of Bi(OTf)3 (2 mol%) affords the corresponding l-phenyl-4-penten-2-ol (Fig. 5). In a similar fashion, various aryl substituted epoxides react smoothly with tetraallyltin to give the corresponding homoallylic alcohols. This method give generality as cycloalkyl oxiranes and sterically hindered ones give the corresponding homoallylic alcohols. 

Bis(ir-allyl)nickel is not formed in this reaction, but the compound be made by condensing nickel vapor with tetraallyltin (131) ... 

Tetraallyltin, triallylphenyltin, and diallyldiphenyltin may be used in place of allyltriphenyltin. 

A partially soluble polyallylscandium triflamide ditriflate 45 was prepared and used to catalyze a three-component coupling reaction.67 An aldehyde, an aromatic amine, and an alkene were mixed in the presence of the catalyst to afford tetrahydroquinolines (equation 17). The catalyst was recovered from the reaction mixtures by precipitation with hexane and could be recycled without loss of activity. Another polymer-supported scandium catalyst was prepared by treating Nafion with scandium chloride to afford the Nafion-scandium catalyst 46.68 This catalyst was used in allylation reactions of carbonyl compounds by tetraallyltin (equation 18). It could be easily recovered by filtration and reused without appreciable loss of activity. 

The iodinolysis of tetraallyltin (see Table 10) is dealt with in Chapter 10, Section 4.1, p. 206. 

THE EFFECT OF IODIDE ION CONCENTRATION ON THE OBSERVED SECOND-ORDER RATE COEFFICIENT, k%", FOR IODINOLYSIS OF TETRAALLYLTIN BY IODINE IN SOLVENT ACETONE AT 20 °C AND IONIC STRENGTH 0.5 M16... 

The term Ar2/AT[I-] corresponds to a mechanism in which the tetraallyltin is attacked by a molecule of iodine, probably by mechanism SE2 (open)16, equation (38) (R = allyl). 

The ratio of the rates of iodinolysis, tetraallyltin trimethylparamethoxyphenyl-tin, was found16 to be 1.3 x 103 using solvent acetone at 20 °C. Since the reactivity ratio for iodinolysis in solvent methanol at 20 °C of trimethylparamethoxyphenyl-tin tetraethyltin is 3.4 xlO4, it may be deduced16 that tetraallyltin is about 4 x 107 times as reactive as tetraethyltin towards iodine. 

Maruoka has reported that chiral bimetallic Lewis acid catalysts 9-11, prepared from (S)-BINOL, M(0-i -Pr)4 (M=Ti, Zr, Hf), and the corresponding spacer, strongly enhance the reactivity of aldehydes or ketones toward allyl transfer from allylstannanes [18-20]. For example, treatment of acetophenone (42) with tetraallyltin (41) in the presence of 30 mol% of the chiral bidentate Ti(IV) catalyst 10 provided the (S)-enriched homoallylic alcohol 43 in 95% yield with 90% ee (Scheme 2) [19]. A suggested reaction mechanism involves double activation of carbonyls owing to the simultaneous coordination of two Ti atoms to a carbonyl oxygen atom. 

Chiral Bronsted acids can also promote the asymmetric addition of allylic tin reagents to carbonyl compounds. Baba and coworkers have found that a stoichiometric amount of (fl)-BINOL (37) acts a chiral promoter for the allylation of unactivated ketones with tetraallyltin and in the presence of MeOH, the corresponding nonracemic tertiary homoallylic alcohols are obtained with up to 60% ee [50]. Later, Woodward et al. improved this process and achieved a catalytic enantioselective allylation of aryl ketones by employing (fl)-monothio-binaphthol 36 as a chiral Bronsted catalyst [49]. For instance, in the presence of 20 mol% of the chiral acid 36 and 40 mol% of H20 in toluene, acetophenone (42) was allylated by a 0.7 0.3 mixture of tetraallyltin (41) and butyltriallylltin (55) to give the (jR)-enriched allylated product 56 almost quantitatively with 89-86% ee (Scheme 8). 

The accurate determination of rate constants for the reactions of 19F atoms is often hampered by the presence of reactive F2 and by the occurrence of side reactions. The measurement of the absolute concentration of F atoms is sometimes a further problem. The use of thermal-ized 18F atoms is not subject to these handicaps, and reliable and accurate results for abstraction and addition reactions are obtained. The studies of the reactions of 18F atoms with organometallic compounds are unique, inasmuch as such experiments have not been performed with 19F atoms. In the case of addition reactions, the fate of the excited intermediate radical can be studied by pressure-dependent measurements. The non-RRKM behavior of tetraallyltin and -germanium compounds is very interesting inasmuch as not many other examples are known. The next phase in the 18F experiment should be the determination of Arrhenius parameters for selected reactions, i.e., those occurring in the earth s atmosphere, since it is expected that the results will be more precise than those obtained with 19F atoms. 

Besides Lewis acids, tetraallyltin is activated by methanol to promote the reaction with aldehydes or activated... 

Reaction of la with tetraallyltin produces the rp-allyl complex... 

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