Condensation of Phenols and Naphthols With Styrene

Phosphorous Acid-Catalyzed Alkylation of Phenols with Alkenes

“…The reaction showed an interesting selectivity. Reaction of the simplest phenol with 2a under the optimized conditions gave the para -alkylated product ( 3o ) in 52% yield with the ortho -alkylated product ( 3o′ ) in 32% yield, which was consistent with other reaction systems. , In sharp contrast, when 3,5-dimethylphenol that possesses both ortho and para electrophilic sites was adopted in this reaction, an 86% yield of the ortho -alkylated product ( 3p ) was obtained with 95% regioselectivity, and only a trace amount of the para -alkylated product was observed. Interestingly, the reaction of o -cresol that has an o- methyl group showed para selectivity, and the para -alkylated product ( 3q ) was obtained in an 84% yield with 90% regioselectivity.…”

“…Investigations of the catalytic performance of other acid catalysts showed that the phosphorus-containing inorganic acids had unique performance for the electrophilic addition reaction (Table , entries 1–3). In comparison, typical Brønsted acids and Lewis acids, such as H 2 C 2 O 4 , TsOH, H 2 SO 4 , TFA, HOAc, FeCl 3 , CuCl 2 , and AlCl 3 , that are efficient catalysts in other catalytic systems , were not compatible under the mild reaction conditions (Table , entries 4–11, respectively). This result demonstrated an attractive feature of H 3 PO 3 catalysis, which allowed the reaction to take place under mild conditions.…”

“…It should be noted that although alkylation products are richer in electrons, the overalkylation products were either not observed or observed in only trace amounts (<1%) in the reactions mentioned above. The unique selectivity was probably due to the dual roles of the phosphorous acid ( vide infra ) and might be applied to selective synthesis of ortho -, meta -, or para -alkylated products, which cannot be easily obtained by other methods. − This catalytic system was also suitable for polyhydroxy phenols. For example, hydroquinone was successfully transformed to the alkylated p -benzenediol ( 3u ) in 80% yield.…”

“…Among the numerous studies of the selective functionalization of phenols, the catalytic alkylation of phenols with alkenes − is one of the most promising approaches because it could form industrially useful alkylated phenols directly from easily available starting materials . Typically, the reaction proceeds via Friedel–Crafts type alkylation, which is generally catalyzed by strong Lewis acids (TiCl 4 , AlCl 3 , FeCl 3 , and ZnBr 2 ) and Brønsted acids (HF and H 2 SO 4 ). , Acidic materials such as graphene, zeolite, mesoporous and nanoporous materials, and amberlyst resin have also been successfully developed as catalysts for this reaction. Recently, the transition metal (Rh, Ir, and Re)-catalyzed addition of phenols to alkenes via C–H bond activation has emerged as a good alternative to this type of reaction.…”