SYNTHESIS OF THE STERICALLY HINDERED BIS(PENTACHLOROPHENYL)ACETIC ACID AND DERIVED STABLE FREE-RADICALS

Bis(pentachlorophenyl)acetic acid esters were synthesized from the alpha-hydroxydiaryl acetate esters 13 via the free radicals 15 formed on homolytic cleavage of the alpha-chloro compounds 14. The acid 8 underwent rapid decarboxylation in basic solution (e.g., Et3N in THF) but could be dehydrated to the corresponding ketene 17. Nucleophilic addition to the ketene provided a route to the corresponding amides (21 and 19) and nitrile 20, the enolates of which underwent ready oxidation to the corresponding stable free radicals 15, 22, and 23. Evidence for the structure and unusual stability of these free radicals is presented. Attempts to observe enols of acids or esters on the addition of water or alcohols to the sterically hindered ketene 17 were unsuccessful.