The chemistry of arene imines. IV. An unusual silver promoted transformation of N‐chlorophenanthrene 9,10‐imine into 9,10‐phenanthrenequinone dialkyl acetals

Abstract

AbstractMethanolic silver nitrate and perchlorate convert N‐chlorophenanthrene 9,10‐imine (1) into 10,10‐dimethoxy‐9(10H)‐phenanthrone (2) in 60% yield. Substitution of the mthanol by ethanol, 1‐ and 2‐propanol gives phenanthrenequinone diethyl‐, di‐1‐propyl‐ and di‐2‐propylacetals (3‐5), respectively. Silver acetate promotes these transformations only in the presence of a protic acid. The reaction mechanism is assumed to involve the generation of a cyclic nitrenium ion, nucleophilic ring opening by methanol, hydrolysis of the imine function and silver ion promoted oxidation.