The Mechanism and Stereochemistry of Chlorination of 2,4-Dichloro-3,,5,6-trimethylphenol and 2,4-Dichloro-3,6-dimethylphenol

Electrophilic attack of chlorine on 2,4,6-trichloro-3,5,6-trimethylcyclohexa-2,4-dienone (2a) gives the trans-pentachloro ketones (3a) and (4a), while similar reaction of 2,4,6-trichloro-3,6-dimethylcyclohexa-2,4-dienone (2b) gives the trans- pentachloro ketones (3b) and (4b), resulting from 2,5- and 4,5-addition of chlorine. The probable stereochemistry of chlorine addition in ketones (3b) and (4b) is determined by chlorination of 2,4-dibromo-3,6-dimethylphenol (6). X-Ray crystal structures are reported for compounds (3a,b), (7) and (8).