Abstract
Synthesis of tri- and tetra-iodoallene (III and IV) from 3-bromo-1-propyne (I) was described. III and IV are very susceptible to autoxidation and both the autoxidation and a solvolysis occurred in aqueous tetrahydrofuran or alcohols to afford the following products depending on the solvents. The reaction of III in aqueous tetrahydrofuran gave triiodoacrdein (XVI) and cis-2, 3-diiodoacrylic acid (XVa). The reaction of III in methanol gave XVI and methyl cis-2, 3-diiodoacrylate (XVb). The reaction of IV in aqueous tetrahydrofuran, methanol, or ethanol gave triiodoacrylic acid (XIIIa), methyl triiodoacrylate (XIIIb) or ethyl triiodoacrylate (XIIIc), respectively. The formation of III from 1, 3-diiodopropyne (II) by the action of alkali was well explained in terms of intermediate formation of the allenic carbanion (IX) followed by the iodination of IX with the hypoiodite resulted from the ethynyl iodine of III. A reaction mechanism involving the intermediate formation of the epoxides (XXIII) and their isomerization to the corresponding carbonyl compounds with the 1, 2-iodide shift gave a good explanation proposed for the oxygenolytic solvolysis of III and IV.
