The reductionof 2-butenyl-mercuric (crotyl-mercuric) systems, RHgX where X = Cl, Br, OCOCH3, by sodium borohydride and trimethyltin hydride has been investigated and under all conditions examined, 1-butene is the sole organic product. Crotylmercuric hydride seems likely to form and then to undergo either intramolecular transfer of hydrogen from mercury to carbon in an SNi′ manner, or SN2′ displacement of mercury by some hydride species leading to 1-butene, or reactions producing crotyl-Hg1 or crotyl-Hg- which are cleaved by water or methanol to again yield 1-butene. π-Crotylpalladium chloride on reduction yields only trans-2-butene, but in the presence of increasing concentratins of triphenylphosphine, which promotes the π ⇄ σ equilibrium of allylpalladium chloride systems, substantial amounts of 1-butene are formed.In aqueous tetrahydrofuran, sodium borohydride converts venzylmercuric chloride cleanly to divenzylmercury. Reduction by tetramethylammonium borohydride in benzene, yields toluene (70%) and dibenzylmercury(30%) whereas toluene was the only product from trimethyltin hydride reduction.