Highly Selective Carbon-carbon Bond Cleacage by Super-protic Directory Groups

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The group 14 organometallic groups have been known to stabilize a carbocations locating at their <beta>. In this project, several extentions of this concept were investigated for seceloping highly selective cleavage processes of a -bond, such as carbon-carbon bonds unser moderate consitions Several<beta>-tri- methylsilylketoxime acetates were found to induce the highly regio-and strtro- specific Beckmann fragmentation to yield the corresponding alkeyl cyanides by an electrophilic activation with trimethylsilyl triflate. This methodology was much superior to the more common activation of a Si-C bond with flurides. This new fragmentation is particularly useful to the stereospecific fromation of olefins as exemplified by synthesis of several insect pheromones. Streroselective introduction of both metallyl function and the carbon moiety was achieved by the conjugate addition of alkenones in one-pot.Alternatively, the organostannyl substituted ketoximes were found to cleave their <beta>-carbon-carbon bonds by oxidative activation with lead tetraacetate. This new process was also highly regio-and stereospecific to furnish alkenyl nitrile oxide intermediates, Which undergo intranolecular dipolar cycloadditions sponta- neously to give <DELTA>-isoxazolines. The super-protic natureof group 14 organo- metallyl groups was also applied to the selective decartboxylation of <beta>-metallyl- carboxylic acids and to the pyrazoline formation of tin-substituted hydrazines.Modification of the cationic center to carbon to a transition-metal, an allylbromoruthenium(IV) moiety, resulted in an unprecedented silver fluoride activation of a carbon-silicon bond by way of a new methyl group migration from silicon to ruthenium atoms.