Hypervalent Interactionsin the Reactions Onium Salts of Main Group Elements

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Reactions of 1-decenyl (phenyl) iodonium salt with halide ions gave substitution products of complete inversion as well as n-elimination products. Analyses of UV spectroscopic and kinetic dependences on the halide concentrations show that the reactions occur via a hypervalent intermediate, lambda^3-haloiodane, formed in a rapid pre-equilibrium. By contrast, 2-halo-1-decenyl-iodonium salts gave substitution products of complete retention of configuration. This reaction is concluded to proceed via a ligand-couplingmechanism within an intermediatehaloiodane.Solvolysis of styryl (phenyl) iodonium salt gave substitution products of both retention and inversion. Deuterium labeling experiments show that complete scrambling of the isotope between alpha and beta positions of the retention product but not of the inversion product. These results imply that the retention product is formed through a vinylenebenzenium ion while the inversion occurs by the in-plane S_N2 mechanims.ALPHAbeta, beta-dialkylvinyliodonium salt gave a variety of products of extensive rearrangement of the beta-alkyI groups on solvolysis as well as reactions with halide ions. The alkyl group trans to the leaving iodonio group rearranges more readily than the cis group, but the cis group does rearrange significantly. Formation of the unrearranged substitution products is not stereospecific. These results are compatible with a reaction occurring mainly via beta-alkyl participation accompanied by a primary vinylic cation as an intermediate.Rates for the reactions of 1-adamantylsulfonium salt with halide ions increase with halide concentration following a saturation curve. This strongly suggests intermediate formation of a hypervalent halosulfurane during this reaction.