Lithiation of 2-aryl-2-methyl-1,3-dioxolanes with PMDTA-complexed butyllithium

The metalation of chloro- and methoxy-substituted acetophenone ketals with butyllithium (BuLi) and with N,N,N′,N″,N″-pentamethyldiethylenetriamine-complexed butyllithium (BuLi/PMDTA) has been investigated. The lithio species thus generated were carboxylated to benzoic acids. Lithiations with BuLi occurred regioselectively ortho to the ketal substituent. When using BuLi/PMDTA, a regiodivergent behavior has generally been found in the lithiations. However, in some cases a significant selectivity was observed, enabling the preparation of the main regioisomer, exhibiting a new substitution pattern, with reasonable yield.