Pschorr Reactions with Sulphonamides derived from N-Benzyl-o-phenylenediamine: A New Route to Phenanthridine, and a New Type of Molecular Rearrangement

Abstract

The preparation in three steps of N-benzyl-N-benzenesulphonyl-o-phenylenediamine (Va), of N-benzyl-N-p-toluenesulphonyl-o-phenylenediamine (Vb), and of N-benzyl-N-methanesulphonyl-o-phenylenediamine (Vc) from o-nitroaniline is described. The copper-catalysed decomposition of diazonium salts of each of these amines in acetic acid-sulphuric acid has been examined. Compound (Va) gave N-benzyl-2-aminobiphenyl (IXa), 5-benzenesulphonyl-5,6-dihydrophenanthridine (VIa), N- benzyl-2-aminobiphenyl-2'-sulphonic acid sultam (Xa), N-benzenesulphonyl-2-amino-biphenyl (XIIa), and phenanthridine. Compound (Vb) gave N-benzyl-2-amino-4'-methylbiphenyl (IXb), 6-p-toluenesulphonyl-5,6-dihydrophenanth (VIb), a compound C₂₀H₁₇NO₂S thought to be N-benzyl-2-amino-5'-methylbiphenyl-2'-sulphonic acid sultam (Xb), N-benzyl-N-p-toluenesulphonylaniline (XIb), N-p- toluenesulphonyl-2-aminobiphenyl (XIIb), and phenanthridine. Compound (Vc) gave 5-methanesulphonyl-5,6-dihydrophenanthri (VIc), N-benzyl-N-methanesulphonylaniline (XIc), N-methanesulphonyl-2-aminobiphenyl (XIIc), and phenanthridine. It has been found that the yields of most of these products depend inter alia on the excess of sodium nitrite present during the diazotization prior to cyclization. It is suggested that this effect is caused by changes in the concentration of cuprous ions present during the cyclization. Heterolytic and homolytic processes may be involved in the formation of the dihydrophenanthridines and sultams. The formation of the biphenyl derivatives (IX) and (XII) is postulated to proceed via the spirane intermediates (XIX) or (XX). The conversion of the sulphonamides of dihydrophenanthridine (VI) to phenanthridine in c. 70% yield completes new syntheses of this ring system.