V. Reactions of Nitro Compounds with Silanes

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Concerns with the toxicity of tri-n-butyltin hydride and the purification problems that accompany its use have spawned a variety of attempts to replace this reagent with a less troublesome one (see Appendix I). Tris(trimethylsilyl)silane normally is an attractive alternative to Bu₃SnH, but it fails completely in this role in group replacement reactions in nitro compounds. The reason for failure is that the radical formed by addition of (Me₃Si)₃Si· to a nitro group does not break the carbon–nitrogen bond required for group replacement but rather cleaves a nitrogen–oxygen bond to begin a sequence of reactions leading to a complex reaction mixture (Scheme 13).⁴⁸

A more effective procedure for reducing the amount of tri-n-butyltin hydride needed for nitro-group replacement with a hydrogen atom consists of regenerating Bu₃SnH from the Bu₃SnNO₂ formed during the substitution process. A pair of reactions that achieve group replacement and regenerate Bu₃SnH are given in equations 11 and 12. This alternative method requires only 10% of the tri-n-butyltin hydride needed in the standard procedure.⁴⁹