Regiospecific Synthesis of Ortho Substituted Phenols

Phenol is highly reactive toward electrophilic aromatic substitution. By this general approach, many groups can be appended to the ring, via halogenation, acylation, sulfonation, and other processes. Phenol contains the hydroxyl group (–OH), which is a strongly activating ortho/para directing group in aromatic electrophilic substitution (AES). AES gives a mixture of ortho-and para isomers, which must be separated. The strong directing ability of phenol can also result in multiple substitutions on the aromatic ring which could be a major concern in the regiospecific synthesis of phenols. AES and Directed ortho--Metalation (DoM) are the only ways to directly substitute a proton on an aromatic ring and to synthesize regiospecifically substituted phenols. Phenol is a versatile precursor to a large collection of drugs, most notably aspirin, but also many herbicides and pharmaceuticals. AES reactions are useful in regiospecific synthesis as a way of introducing many reactive groups on the benzene ring and also help us to design a suitable method for synthesizing compounds in an efficient manner. Dimethylbenzylamine products are obtained as a result of the reaction of phenols with Eschenmoser’s salt (N,N-Dimethylmethyleneiminium iodide). This approach enables us to prepare regiospecifically ortho substituted phenols by using the AES protocol. We have discovered that Eschenmoser’s salt has the ability in basic medium containing triethylamine (TEA) to remove the proton and bond to the aromatic ring exclusively in ortho position to the –OH substituent. Our research work focused on efforts to render isolated products with minimum impurities, greener and more atom economical by use of limiting reagent in the reactions. For the purpose of evaluation of the obtained compounds and intermediates we use Gas Chromatography (GC), Gas Chromatography coupled with Mass Spectrometry (GC-MS) and Nuclear Magnetic Resonance (NMR). Our future work is to synthesize novel benzoheterocyclic compounds from the ortho-derivatised phenols as well as multi-substituted aromatic compounds. The dimethylamino methyl group can act as a directing group in the ortho-lithiation process; subsequent ortho--metalation and treatment with electrophiles generates 1,2,3- trisubstituted phenolic derivatives. Thus, phenolic precursors can be transformed into numerous derivatives which can be used in the chemical, agricultural and pharmaceutical industries