Directing effects in nitration of 1-adamantyl bearing aromatic ketones

Abstract

Nitration of four 1-adamantyl bearing aromatic ketones with mixed acid, acetyl nitrate, silver nitrate and guanidine nitrate was studied under various conditions. The ketones with conjugated carbonyl group or with a benzyl group were examined and a considerably high amount of ortho isomer was observed in all cases. The proportion of ortho nitration showed the same trends for both examined groups of ketones. Unprecedently, the ortho isomer was formed quantitatively upon the reaction of 1-(1-adamantyl)-3-phenylpropan-2-one with acetyl nitrate in acetic anhydride. Influence of electronic, steric and complexation effect of carbonyl group on regioselectivity is discussed. An alternative reaction pathway including complexation of nitrating agent and a pre-equilibrium of protonated and nitronium coordinated carbonyl in particular is suggested to play crucial and general role in nitrations of aromatic carbonyl compounds.