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The solvolysis of 7,7-bis(trifluoromethylsulfonyloxy)-2-norbornene ( 1a ), 1-trifluoromethylsulfonyloxy-1-phenylethylene ( 2a ), 2-methyl-1-cyclohexen-1-yl triflate ( 3a ) and 4-camphenyl triflate ( 4a ) in carbon disulfide or diethyl ether with added MgI 2 and MgBr 2 yields a mixture of the corresponding halides 5b-e, 6b-c, 7b-c and 8b-c . The ionization of the triflate group is favoured by coordination with the magnesium halides. The reaction with MgI 2 was found to be second-order and is about 50 times more reactive than MgBr 2 . The selectivities of the intermediate cations 5–8 toward the nucleophiles MgI 2 and MgBr 2 are nearly constant, although the solvolysis rates differ by more than three powers of ten. A theoretical explanation of the constant selectivity principle is given. |
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