Reduction of organotin halides

Supported Ditin Reagents. Ditin reagents can be obtained by reduction of organotin halides with arene metal radical anions or by dehydrogenation of supported organotin hydrides in the presence of Pd(PPh3)4 (Scheme 5.5.13) ... 

Less satisfactory methods for preparation of the simple organotin hydrides include reduction of organotin halides with amalgamated aluminum and water (22), and the reaction of organotin sodium compounds with ammonium bromide in liquid ammonia (23, 24). 

The organotin hydrides in Tables 122 and 12 are prepared by reduction of organotin halides with ... 

An application of the reduction method of organotin halides by simple organotin hydrides is the preparation of l, >-bis(hydridodimethylstannyl)alkanes235 ... 

In aprotic eatholytes, the cathodic reduction of alkyl halides at Sn cathodes leads to organotin compounds 427 428) ... 

Organotin hydrides are advantageous as reductants in terms of their facile availability, stability, and reactivity. - Almost all tin hydrides are liquids, and stoichiometric tin-hydrogen bonds can be used. In general, the tin hydride reductions have been performed under radical conditions using initiators such as azobisisobutyroni-trile (AIBN), triethylborane, and UV irradiation. The reduction of organic halides and pseudohalides by tri- -... 

Reductive dehalogeuation of alkyl halides. Lithium aluminum hydride has commonly been used only for reductive dchalogenation of reactive substrates organotin hydrides, for example tri- -btityltin hydride (I. 1192-1193 2, 424 3, 294), have been used for reduction of inert halides. Recently JeflToid ei al. have reported that supposedly inert halides are reducible by lithium aluminum hydride. Thus the vinyl halide (I) is reduced to (2, endb-2-phenylbicyclo[3.2. l]octene-3) by lithium aluminum hydride in refluxing ether (24 hr.). 3-Bromobicyclo[3.2.l]octene-2 is reduced to the parent... 

The mechanism for reduction of alkyl halides is not always nucleophilic substitution. For example, reductions with organotin hydrides generally " take place by free-radical mechanisms,as do those with Fe(CO)5. Alkyl halides, including fluorides and polyhalides, can be reduced with magnesium and a secondary or ter-... 

The reduction of chlorodeoxy sugars has been achieved [31,32] in high yield by means of tributyltin hydride in the presence of 2,2 -azobis(2-methylpropionitrile). The reaction with methyl 2,3-di-0-acetyl-4,6-dichloro-4,6-dideoxy-a-D-galactopyranoside at 60°C gave [31] methyl 2,3-di-0-acetyl-6-chloro-4,6-dideoxy-ot-D-xylo-hexopyranoside as the main product. A free-radical mechanism has been proposed [33] for the reduction of alkyl halides by organotin hydrides. In accordance with this proposal, the presence of the radical initiator 2,2 -azobis(2-methylpropionitrile) was essential for the reduction of chlorodeoxy sugars moreover, the relative reactivities of the two chlorine atoms in methyl 2,3-di-0-acetyl-4,6-dichloro-4,6-dideoxy-a-D-galactopyranoside follow a free-radical order. 

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). 

Reduction of the halides with a metal hydride such as lithium aluminium hydride, sodium borohydride, or poly(methylhydrosiloxane) gives the corresponding organotin hydrides These have an important place in organic synthesis for the reduction of halides to hydrides (hydrostannolysis) and the addition to alkenes and alkynes (hydrostannation), by radical chain reactions. Further reactions may intervene between the pairs of reactions shown in Equations (1.1.3) and (1.1.4), and (1.1.4) and (1.1.5), and these reactions are particularly useful for inducing ring-closure reactions. 

It should also be mentioned that polymers A-D have to be washed correctly in order to remove the soluble organotin species resulting from the synthesis. This aspect has been studied in detail for polymer C and when it was used for the reduction of organic halides, soluble organotin residues... 

Organotin hydrides have proved to be very effective reagents for the reduction of alkyl halides under homolytic conditions in the presence of radical initiators like AIBN or benzoyl peroxide. Tributyltin hydride (TBTH) is the most commonly employed reagent (equation 48), but others like Bu2SnH2 have found utility (equation 49) . 

Organotin hydrides are synthesized by the reduction of the halides or oxides with lithium aluminum hydride (66). The tin atom of these halides and oxides is softened to a large extent by the organic ligands therefore, it is a better partner for the hydride ion than aluminum. 

Use of mild conditions was crucial and the development of diimide reduction of singlet oxygenates, silver-salt-assisted displacement of halide by peroxide nucleophiles, peroxymercuration and demercuration, peroxide transfer from organotin to alkyl triflates, and oxygen trapping of azoalkane-derived diradicals have all played a part in providing the rich harvest of new bicyclic peroxides described herein. 

Organotin hydrides R SnI L- , where R represents an alkyl or aryl group, are generally prepared quite easily by reduction of the corresponding organotin halides using either LiAlFLt or NaBFL in ether or dioxane ... 

The dehalogenation of organic halides by organotin hydrides takes place in most cases with a free-radical mechanism [1, 84, 85], The stereospecific reduction of 1,1-dibromo-l-alkenes with Bu3SnH discovered by Uenishi and coworkers [86-89], however, did not occur in the absence of palladium complexes and did not involve radicals. For the synthesis of (Z)-l-bromo-l-alkenes, [(PPh3)4Pd] proved to be the most effective catalyst which could also be generated in situ. The reaction in Eq. (7) proceeded at room temperature and a wide range of solvents could be used. 

Selective reduction of halides.1 Thecomplexl reduces tertiary halides to alkanes without attack on primary or secondary halides. It is more selective than organotin hydrides. Benzylic and allyl halides are also reduced easily. The reagent reduces a mixture of the halides 2 mainly to trims-3 thus, a partial inversion oftonfiguration is... 

---