Polyhalogenoaromatic compounds. Part 40. Synthesis and thermal rearrangements of some polychloropyridines

Abstract

The ethers (1), (2), and (7)–(10) were prepared by alkylation of tetrachloro-4(or 2)-hydroxypyridine. Alkylation of the 2-hydroxy-compound also gave the 1-alkyltetrachloro-2-pyridones (15)–(18)(Table). Allyl (3) and propargyl (4) tetrachloro-4-pyridyl sulphides were prepared similarly, and the latter rearranged to allenyl tetrachloro-4-pyridyl sulphide (5). Allylamine reacted with pentachloropyridine 1-oxide by displacement of an α-chlorine atom, sodium benzyloxide and aflyloxide gave only the 1-alkoxytetrachloro-2-pyridones (12) and (13), whilst under the same conditions sodium propargyloxide gave a mixture of (14) and the 1-oxide of ether (10). Allyl tetrachloro-4-pyridyl ether (1) underwent a Claisen rearrangement to give a mixture of 4,6,7-trichloro-2-methyl (and chloromethyl)-2,3-dihydrofuro[3,2-c]pyridine, (22) and (23), 3-allyl-2,5,6-trichloro-4-hydroxypyridine (21)(major product), and tetrachloro-4-hydroxypyridine. In NN-diethylaniline at 230 °C, propargyl tetrachloro-4-pyridyl ether (2) gave tetrachloro-4-hydroxypyridine and tetrachloro-4-ethoxypyridine; the latter product was shown to arise by attack of the hydroxy-compound on the solvent. Allyl tetrachloro-2-pyridyl ether (7) rearranged thermally to give only 1 -allyltetrachloro-2-pyridone (15), whilst the corresponding crotyl (8) and dimethylallyl (9) ethers gave only tetrachloro-2-hydroxypyridine and starting material. Attempts to thermally rearrange compounds (3), (4), (6). (10), and (11) gave either starting material or an intractable product.