An Efficient Scale-Up Process for the Preparation of the APD334 Precursor 4-Chloromethyl-1-cyclopentyl-2-(trifluoromethyl)benzene

Synthetic studies of the APD334 precursor 4-chloromethyl-1-cyclopentyl-2-(trifluoromethyl)benzene (6) are described. A two-step scalable process was developed starting from commercially available and inexpensive starting materials. An iron(III) chloride-catalyzed aryl–alkyl cross-coupling reaction provided the intermediate 1-cyclopentyl-2-(trifluoromethyl)benzene (9), which was converted to the target building block 6 by a direct regioselective chloromethylation reaction with trioxane/thionyl chloride or chlorosulfonic acid in sulfuric acid. The process was transferred to pilot-plant scale to produce >100 kg of 6 with >98 area % HPLC purity.