Regioselective Nitration of 4′-R-Dibenzo-18-Crown-6 by Some Alkaline Metals Nitrates in Polyphosphoric Acid

We have studied the effect of the substituent nature on nitration of 4′-R-dibenzo-18-crown-6 (DB18C6, where R is NO2, CH3CO, or C2H5) in polyphosphoric acid (PPA). We also studied the influence of cations' nature on regioselectivity of nitration. It was found that electron withdrawing substituents direct the incoming NO2-group mainly to the 4″-position of the unsubstituted benzene ring in the reactions with lithium nitrates. If there are two substituents: electron releasing and electron withdrawing in one benzene ring, then the orientation effect of the latest one is stronger. The obtained results once more confirmed the existence of ‘transannular transmission’, which we first of all observed during the acetylation of DB18C6. Based on these observations preparative methods leading to 4′,4″-dinitro-DB18C6, 4′,5″-dinitro-DB18C6, 4′-acetyl-4″-nitro-DB18C6, 4′-acetyl-5″-nitro-DB18C6, 4′-ethyl-5′,5″-dinitro-DB18C6, and 4′-ethyl-5′,4″-dinitro-DB18C6 have been developed.