Relative ease of formation of carbonium ions and vinyl cations in electrophilic additions

Oxybromination of Ethynylbenzene Catalysed by Molybdenum Complexes in Organic Solvent and in Ionic Liquids

“…We report here the results obtained on reacting ethynylbenzene with H 2 O 2 /KBr. Since bromination of this alkyne is expected to be more difficult than that of styrene, [6] the more reactive Mo(VI) species [7] was used as catalyst. The oxybromination reaction of ethynylbenzene was carried out at room temperature in a two-phase system H 2 O/CH 2 Cl 2 .…”

“…Hydrophobic ILs with the 1-butyl-3-methylimidazolium [bmim þ ] cation were used, with different anions, i.e., hexafluorophosphate, [PF 6 À ], and bis(trifluoromethanesulfonyl)imide, [(CF 3 SO 2 ) 2 N À ]. [9] The results are collected in Table 2.…”

“…First, the reaction performed in water/ILs was faster than that in molecular solvents. The reduced reaction times, especially in bmim PF 6 , had the positive side effect that almost all the consumed ethynylbenzene was converted into the reaction products. Second, yields were comparable, but the selectivity was definitely shifted toward the dibromo ketone (Table 2).…”

“…[14] This mechanistic scheme is in agreement with the experimental results. In fact, the sharp decrease of 1,2-dibromostyrene on going from dichloromethane to bmimPF 6 can be ascribed to different distribution of molecular bromine between the two phases. In the ionic liquid, a more polar medium, [15] where the functionalisation of the substrate is likely to occur, [5] the Br 2 concentration is expected to be lower than in dichloromethane.…”

The reaction of some propargyl alcohols with benzeneselenenyl chloride

“…Several differences are, however, to be noted [I] H,C=C=CHCHZOH P between our individual studies. Because of our prior interest in electrophilic additions to alkynes sea (17)(18)(19)(20)(21), we decided to complete our initial investigation.The results of this study are reported As Drecursors to these allenic alcohols and allenes herein. in general, it was necessary for us to prepare a large number of propargyl alcohols.…”