Metalation of alkynes. Part 2. Behaviour of alkynes with mercury(II) acetate in methanol: a systematic reinvestigation
The reactions of a series of alkynes with mercury(II) acetate, both in equimolar and catalytic amounts, were investigated in methanol. Hex-1-yne, oct-1-yne, oct-4-yne, 1,4-diacetoxybut-2-yne, methyl oct-2-ynoate, methyl 3-phenylpropynoate, oct-2-ynoic acid, phenylpropynoic acid, oct-1-yn-3-ol, 1-ethynyl-cyclohexanol, 1-ethynylcyclohexylamine, phenylethyne, diphenylethyne, and ethynylferrocene were the examined substrates. The non-mercuriated products from the reaction were the corresponding vinyl ether, dialkoxyalkane, and ketone, isolated under preparative conditions. The presence of 0.1% toluene-p-sulphonic acid increased the reactivity. The reactions of oct-1-yne and oct-4-yne were studied in detail by following with time the formation of the products under a variety of conditions, and a mechanistic scheme was drawn. For comparison, styrene, trans-oct-4-ene, and trans-β-methylstyrene were treated with 5 mol % mercury(II) acetate. The reaction of alkenes was found to be non-catalytic.