Synthesis and Novel Rearrangement of 1,1,1-Trichloro-2-alken-4-ones

Abstract

Strong mineral acids convert 1,1,1-trichloro-2-hydroxy-4-alkanones to 1,1,1-trichloro-2-aIken-4-ones and 1,1,5-trichloro-1-alken-4-ones via an intramolecular chlorine shift from C-1 to −5 of an enol allylic system. Alternatively, 1,1,1-trichloro-2-alken-4-ones may be synthesized from 1,1,1-trichloro-2-hydroxy-4-alkanones by acetylation and elimination of acetic acid or by nucleophilic substitution with thionyl chloride followed by dehydrohalogenation. The two diastereomeric 1,1,1-trichloro-2-hydroxy-3-methyl-4-hexanones do not epimerize during acetylation, and the erythro-acetate resists elimination of acetic acid. Pyrolysis of 2-(1-hydroxy-2,2,2-trichloroethyl-)cyclohexanone yields 2-(2,2-dichlorovinyl)-2-cyclohexenone while treatment of 1,1,1,7,7,7-hexachloro-2,6-dihydroxy-4-heptanone with strong acid leads to the formation of 1,1,1,7,7,7-hexachloro-2,5-heptadien-4-one.