Ozone-Mediated Nitration of Phenylalkyl Ethers, Phenylacetic Esters, and Related Compounds with Nitrogen Dioxide. The Highest Ortho Substitution Observed in the Electrophilic Nitration of Arenes

By the combined action of ozonized oxygen and nitrogen dioxide (the kyodai -nitration), the title compounds were smoothly nitrated in dichloromethane at subzero degrees with high ortho positional selectivity. Although the conventional nitration of phenylacetic acid and esters mainly produces m - and p -nitro derivatives, the present nitration offers a simple high-yield synthesis of o -nitro derivatives which are important as precursor in organic synthesis. The proportions of the ortho isomer in the nitration products from methyl 2-phenylethyl ether and methyl phenylacetate were 71 and 88%, respectively, the latter value being the highest ortho isomer proportion so far observed in the electrophilic aromatic nitration. The observed high ortho selectivity has been rationalized in terms of radical cation intermediate and six-membered cyclic transition state.