Organotin compounds allyls

Phthalic anhydride also shows the ability to inhibit thermal destruction of polyolefins [21]. Among the organometallic compounds may be quoted organotin compounds R2Sr(OR )2, where R2 means alkyl, aryl, or cycloalkyl OR means alkoxyl, acyl, or R2Sn(CH2COORi)2, where Rj—Ci—Cm means alkyl, allyl, or benzyl Ro represents chloro-, mono-, or triorga-notin mercaptans [22,23]. 

This type of metallic exchange is used much less often than 12-32 and 12-33. It is an equilibrium reaction and is useful only if the equilibrium lies in the desired direction. Usually the goal is to prepare a lithium compound that is not prepared easily in other ways, for example, a vinylic or an allylic lithium, most commonly from an organotin substrate. Examples are the preparation of vinyllithium from phenyl-lithium and tetravinyltin and the formation of a-dialkylamino organolithium compounds from the corresponding organotin compounds ... 

Reactions of Allylic Trialkylstannnanes. Allylic organotin compounds are not sufficiently reactive to add directly to aldehydes or ketones, although reactions with aldehydes do occur with heating. 

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... 

Tin compounds can be produced by the Nalco-type reactions39 as well as by Cd and Zn mediated methods42,43. The use of organotin compounds in electrodically induced transmetallations has also been described in a study in which Grignard-type allylation of carbonyl compounds has been carried out by electrochemically recycled allyltin reagents44. 

As with the silanes, some of the most useful synthetic procedures involve electrophilic attack on alkenyl and allylic stannanes. The stannanes are considerably more reactive than the corresponding silanes because there is more anionic character on carbon in the C—Sn bond and it is a weaker bond.103 104 There are also useful synthetic procedures in which organotin compounds act as carbanion donors in palladium-catalyzed reactions, as discussed in Section 8.2.3 Organotin compounds are also very important in free-radical reactions, which will be discussed in Chapter 10. 

Organometallics. Organotin compounds, l SnR, in which R is alkyl and R is homounsaturated (allyl, benzyl), exhibit lower ionization potentials than saturated analogs (Table 4). These values are in the range of other donors which effect reduction of... 

As organotin compounds (organostannanes) undergo smooth Pd-catalysed transmetallation, aryl halides react with a wide variety of aryl-, alkenyl- and alkylstannanes [139]. Coupling with allylstannane is the first example [140]. The reaction is called the Migita-Kosugi-Stille or Stille coupling. Aryl, alkenyl, allyl, alkynyl and benzyl... 

Organotin compounds may be synthesized by the cathodic reduction of organic compounds in the presence of tin halides. For example, the reduction of allylic halides in the presence of chlorostannanes gives the corresponding allylstannanes in good yields [69]. Combination of this reaction with in situ palladium-catalyzed reaction with allylic halides leads to effective formation of the head-to-tail homo coupling products as shown in Eq. (17). 

Grignon, J., Pereyre, M. Mechanism of the substitution of halogen derivatives by allylic organotin compounds. J. Organomet. Chem. 1973, 61, C33-C35. 

Organotin compounds are used in many synthetic procedures as stoichiometric reagents (hydrostannolysis, hydrostannation, allylation, Stille coupling, Sn/Li transmetallation, transesterification, etc), and this presents the problem of removing the organotin residues from the required product. This is particularly important in the preparation of pharmaceuticals as these organotin compounds are to some degree toxic. 

---