Dimerization of 2,2-dimethyl-1,2-dihydrobenzo[f]isoquinoline

Abstract

Cyclic Schiff bases are used in organic synthesis [1]. We previously synthesized 3,3-dialkyl-3,4-dihydroisoquinolines and their benzo[f] derivatives and examined some properties of these compounds [2, 3]. While continuing studies in this field, we found that heating of 2,2-dimethyl-1,2-dihydrobenzo[f]isoquinoline (I) in boiling toluene on exposure to air leads to the formation of dimer II. It also turned out that dimer II was formed when compound I was kept in solution or in the crystalline state on exposure to air. Heating of a solution of I in a stream of argon or prolonged storage (12–15 years) of its crystalline sample at 20– 25°C in a closed vessel did not lead to formation of dimer II. These findings indicate that dimerization is the result of oxidation process. metric, and the benzoisoquinoline fragments therein are turned with respect to each other about the C 1 –C 16 bond, the torsion angle N 1 C 1 C 16 N 2 being 120.9°; the planes of the naphthalene fragments are almost orthogonal to each other (88.2°). Unlike initial compound I, the 1 H NMR spectrum of II lacked signal of CH=N proton.