catalysts were found to be the optimal catalysts (See SI for optimization studies). Product formation was not observed in the absence of iron catalyst and the use of AlCl3 in place of FeX3/HX resulted in complex mixtures. The ability to use tertiary alcohols enables various alkyl groups to be added (Scheme 5). Alkylation of phenol (1) occurred selectively at the para position, affording 3aa-3ad in 71-85% yields. Adamantane is a privileged structure that has earned the reputation of being a "lipophilic bullet" for enhancing pharmacological activity and various methods have been devised for their derivatization, 33 including a Friedel-Crafts strategy that requires trifluoroacetic acid as the solvent. Here, dual FeCl3/HCl catalysis allows arylation of 1-adamantanol under mild reaction conditions. Surprisingly, 1methylcyclopentanol (11e) turned out to be a poor alkylating agent that only gave 23% yield of para-methylcyclopentyl phenol (3ae) even with a higher catalyst loading. Analysis of the reaction mixture revealed the major side product to be cyclopentene. Presumably, the dehydration pathway is facile, and the reverse hydration step is unfavorable under the reaction conditions. Using tert-butanol (11a), alkylation of 4tert-butylphenol furnishes di-tert-butylphenol (3ba) in 85% yield, while 4-ethylphenol was alkylated to yield 3e'a in 58% yield at 1 mol% FeCl3 loading. 4-Chlorophenol required 1 equivalent of FeCl3 to achieve 51% yield of 3ca. 2-Benzyl-, 2ethyl-, and 2-phenylphenol were alkylated in moderate-to-good yields (62-86%) to give 3ka, 3d'a, and 3ga, respectively. Some substrates require higher catalyst loadings (e.g., 2-ethylphenol and 2-phenylphenol) to achieve high reactivity, but absent of a trend. Minor amounts of dialkylation side products were isolated (see SI). tert-Alkylation of meta-substituted phenols were examined using 2-methyl-2-propanol (11b). At 5 mol% catalyst loading, 3-ethyl-, 3-tert-butyl-, and 3-phenylphenol are converted to disubstituted phenols 3eb, 3fb, 3g'b in 67-83% yields. 3-Methoxyphenol is converted to 3ib in 37% yield and alkylated resorcinol 3mb is synthesized in 62% yield. Unlike other meta-substituted phenols, 3-fluorophenol is tertalkylated para to the hydroxy group in 53% yield (3jb). Tertiary benzylic, allylic, and propargylic alcohols 11f-h, normally successful in Friedel-Crafts alkylations, either resulted in a complex mixture of products that could not be separated to homogeneity or no reactivity.