Aryl halides, reduction with organotin

A radical mechanism may also be proposed for the other reductions, at least for the alkyl and aryl halides in view of the clarified relations of their reduction with organotin hydrides (756). For carbonyl or other unsaturated compounds (Table IX), a polar mechanism is also possible it could be of Sn2 type. Further experiments are needed for clarification. 

Stille coupling was also developed in tlie early 1980s and is similar to Suzuki coupling in its sequence. It is used to couple aryl or vinyl halides or triflates with organotin compounds via oxidative addition, transmetallation, and reductive elimination. The oxidative addition reaction has tlie same requirements and preferences as discussed earlier for tlie Heck and Suzuki reactions. The reductive elimination results in formation of tlie new carbon-carbon bond. The main difference is that tlie transmetallation reaction uses an organotin compound and occurs readily without the need for an oxygen base. Aryl, alkenyl, and alkyl stannanes are readily available. Usually only one of tlie groups on tin enters into... 

The use of monosubstituted stannanes RSnXj in aqueous systems allows a dramatic reduction of toxicity hazards associated with volatile organotins. The compounds RSnCls dissolved in aqueous alkali to give stannates [RSn(OH)3+ ]" has been shown to be useful in cross-coupling reactions with water-soluble aryl halides either in a phosphine-free system or in the presence of TPPMS ligand. " ... 

The reduction of alkyl, aryl, and acyl halides by organotin hydrides would suggest that other halides might also be reduced. It has been shown that AT -bromosuccinimide is reduced in 95 % yield with triphenyltin hydride (82). Diphenylchlorophosphine undergoes exothermic reduction with triphenyltin hydride providing diphenylphosphine in good yield (8J). 

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