Allyl halides with organotin compounds

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... 

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). 

Similar dicarborating cis-exo additions are achieved with up to 99 % yield if aryl or vinyl halides and various organotin compounds, such as vinyl-, phenyl-, ethynyl- and allyl(tributyl)tin systems, are added to norbornene in the presence of tetrakis(triphenylphosphane)palladium(0) or di-chlorobis(triphenylphosphane) as catalyst precursor7,30,80-81. Also reported are cis-exo dicarbo-rative additions to the norbornene skeleton, and their application to the synthesis of prostaglandin endoperoxide analogs, which employ stoichiometric amounts of palladium compounds16. 

Hexamethyl- and Hexabutylditin. These ditins undergo cross-coupling with a variety of organohalides and pseudohalides (such as aryl halides, vinyl triflates, acyl chlorides, and allyl halides) in this protocol to give the correponding tin compounds. The reaction is particularly useful for preparation of organotins with labile functionalities that are not compatible with other procedures. 

B.iv.b. Synthesis of 1-Substituted 1,4-Pentadienes. The combination of the above reaction with an organotin reagent constitutes a new reaction to synthesize 1-substituted 1,4-pentadienes in one pot (Scheme 11). The first reaction generates PdCl2 as the catalytic species, which can react with the tin compound R SnBu to yield Bu SnCl and Pd(0) species that can be the active catalytic species in the second reaction. After the first reaction was carried out, excess allyl halide was removed under reduced pressure then the second reaction may be carried out. Thus, two Pd-catalyzed reactions involving different catalytic species of Pd(II) and Pd(0) could be composed into the consecutive one-pot process (Scheme 12). 

In the carbonyl allylation with allylic bromides mediated by tin(ll) halide, organotin(iv) compounds were generally postulated (Mukaiyama et al, 1980). Tin(ll) chloride in the acidic aqueous medium MeOCHjCHjOH/HjO/AcOH/HCl (Uneyama et al, 1986b) or tin(ll) chloride with Amberlyst 15 in THF/HjO (Talaga et al, 1990) served as the promotor in allylation reactions yielding a-methylene-y-lactones. 

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