Synthesis of 4,6‐Dichloro‐ and 4,6‐Difluorophthalides: a Systematic Study on the Lithiation of 3,5‐Dihalo‐N,N‐diisopropylbenzamides
By taking advantage of the N,N-diisopropylcarbamoyl moiety as a versatile ortho-directing lithiation group, the preparation of 4,6-dichloro- and 4,6-difluorophthalides, starting from the corresponding 3,5-dihalo-N,N-diisopropylbenz-amides, is described here. The role of the lithiating agent, the formation of kinetically and thermodynamically favored products, and the marked difference between the dichloro and difluoro derivatives are discussed in detail.