The nitration of alpha- and beta-acylnaphthalenes

The nitration of alpha- and beta-acylnaphthalenes with copper(II) nitrate in acetic anhydride or nitric acid/acetic acid mixtures gives high yields of the corresponding mononitro compounds. The assignment of constitution to these products is made on the basis of extensive H-1 n.m.r. chemicl shift and coupling constant data. In the case of alpha-acylnaphthalenes, with the notable exception of alpha-pivalonaphthone, nitration occurs in the alpha-positions of the unsubstituted ring to give mixtures of 5- and 8-nitro compounds. alpha-Pivalonaphthone gives appreciable amounts of the 4-nitro compound and also of the 8-nitro compound. This result indicates that the pivaloyl group does not shield the 8-position sterically to any significant extent and is effectively electronically neutral, unlike the other acyl substituents, in allowing attack at the alpha-position (position 4) of the acylated ring. This result is ascribable to the lack of coplanarity of the pivaloyl group with the naphthalene system. All of the beta-acylnaphthalenes gave mixtures of 4-, 5- and 8-nitro derivatives in proportions that did not vary significantly with the nature of the acyl group.