Reactions of aryltins

The two most important reactions of aryltin compounds are first, their reaction with electrophiles, when either the tin or the non-tin product may be the aim, or, second, the coupling reactions that they show in the presence of certain transition metals (Equation (51)). 

S.8.5.6.4. by Reaction of Aryltin Compound and Cyciopentadienyltin Compounds with Transition- or Inner Transitlon-Metal-Carbonyl and Other Complexes. 

In this section we shall discuss papers involving solely or predominantly reactions of aryltins, noting where necessary the other types of organotin mentioned. 

G. Copper-mediated Reaction of Aryltin Reagents as Aryl Donors. 517... 

Table 7-2 Reaction of aryltin compounds with electrophiles Ar-SnX3 —> ArE.

A Pd-catalyzed reaction of aryltin trichlorides 25 with norbomene provided the corresponding arylstannylation products 26 and 27 after treatment of the reaction mixture with methyhnagnesium iodide (Scheme The more electron-donating the substituent on the aromatic ring is, the more stable and long-lived the intermediate o--norbomylpalladium complex is, and this leads to an increasing proportion of the product 27. 

Other organometaloids also undergo similar reactions. Analogous Cu(OAc)2 mediated reaction of aryltins, arylsiloxanes, arylbismuth compounds, and arylleads with various amines lead to arylated products in good yields. An interesting modification of amine or amide arylation by aryl boronic acids mediated... 

By reaction with the appropropriate aryl halides can be prepared a variety of aryltin compounds that are not accessible from the reactions involving arylmagnesium halides and organotin halides (88,89) there is evidence that an aryne intermediate may be involved (90). However, for some purposes, such as the addition to carbonyl compounds, ox-iranes, and oxetanes, to give hydroxyalkyltin compounds, the Sn-Mg reagents may have advantages (see Section II,E) (91-93). 

Unactivated aryl iodides undergo the conversion Arl — ArCHj when treated with tris(diethylamino)sulfonium difluorotrimethylsilicate and a palladium catalyst.131 A number of methods, all catalyzed by palladium complexes, have been used to prepare unsymmetrical biaryls (see also 3-16). In these methods, aryl bromides or iodides are coupled with aryl Grignard reagents,152 with arylboronic acids ArB(OH)2,153 with aryltin compounds Ar-SnR3,154 and with arylmercury compounds.155 Unsymmetrical binaphthyls were synthesized by photochemically stimulated reaction of naphthyl iodides with naphthoxide ions in an SrnI reaction.156 Grignard reagents also couple with aryl halides without a palladium catalyst, by the benzyne mechanism.157 OS VI, 916 65, 108 66, 67. 

The palladium-catalyzed reaction of aryl- and vinyl-tin reagents with stereochemically defined allyl chlorides proceeds with overall retention of configuration, indicating that the second step, entailing interaction of the iT-allylpalladium complex and the organotin, proceeds by transmetallation and reductive elimination (attack at Pd, retention) (equations 166 and 167).142145 Comparable results were obtained with cyclic vinyl epoxides and aryltins.143... 

The impurities such as grease, acids, or metals act as catalysts and the driving force of the overall reaction of Eq. (133), once it is initiated, is the formation of a gaseous and solid phase. With careful exclusion of such catalysts, alkyl or aryltin hydrides appear to be stable indefinitely at room temperature. 

Aryltin trichlorides (entry 6) can be used as alternatives to aryltributylstannanes (entry 5) for aryl transfer. The reactions of fluorous tin compounds are relatively slow, but they can be greatly accelerated by microwave irradiation. For example, arylations such as that in entry 7 require about a day for completion under normal conditions, but can be completed in 90-120 s under irradiation.43... 

The Stille coupling involves heating a halide, a stannane and a catalyst in a suitable solvent, such as toluene or DMF. No base is required. The conditions are relatively straightforward, with little overall variation, apart from the catalyst. However, if a triflate is used instead of a halide, the reaction may not succeed, as transmetallation of aryltin compounds with arylpalladium triflates is often difficult. Addition of a halide source, such as lithium chloride, usually solves this problem as it allows the formation of the arylpalladium chloride, which can undergo transmetallation. 

B.iv.c. Stereospecific Synthesis of C-Arylglycosides. The Pd- or Ni-catalyzed reaction of a-O-A -glycopyranoside (1) with arylmagnesium bromides has provided a- or /3-C-aryl-A -glycopyranosides, respectively, exhibiting 100% stereospecihcity in each case " (Scheme 19). A related stndy with aryltins and arylsilicates has also been pnblished.t ... 

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