Stereochemistry of hindered benzophenones: synthesis and resolution of 3-carboxymethyl-2,2′,4,4′,6,6′-hexamethyl-3′-nitrobenzophenone

Abstract

3-Bromo-2,2′,4,4′,6,6′-hexamethyl-3′-nitro-, 2,2′4,5′,6-pentamethyl-3-nitro-, 3-bromo-2,2′,4,6-tetramethyl-5′-nitro-, and 2,2′,4,4′,6,6′-hexamethyl-3-methoxycarbonylmethyl-3′-nitro-benzophenone were prepared by Friedel–Crafts acylation. The last compound was hydrolysed to 3-carboxymethyl-2,2′,4,4′,6,6′-hexamethyl-3′-nitrobenzophenone, which was resolved by way of the brucine salt; this demonstrates for the first time the existence of optical isomerism in suitably substituted benzophenones because of steric interactions between the o- and o′-substituents.