Notes on the Synthesis of Sulfonated Derivatives of 5,6,7,8‐Tetrahydro‐1‐naphthylamine and 5,6,7,8‐Tetrahydro‐2‐naphthylamine
Sulfonation of 5,6,7,8‐tetrahydro‐1‐naphthylamine (1) with sulfuric acid gave a mixture of 1‐amino‐5,6,7,8‐tetrahydronaphthalene‐2‐sulfonic acid (2), 4‐amino‐5,6,7,8‐tetrahydronaphthalene‐2‐sulfonic acid (13) and 4‐amino‐5,6,7,8‐tetrahydronaphthalene‐1‐sulfonic acid (3). The same reaction with 5,6,7,8‐tetrahydro‐2‐naphthylamine (20) yielded 3‐amino‐5,6,7,8‐tetrahydronaphthalene‐2‐sulfonic acid (21); formation of 2‐amino‐5,6,7,8‐tetrahydronaphthalene‐1‐sulfonic acid (16) or of 3‐amino‐5,6,7,8‐tetrahydronaphthalene‐1‐sulfonic acid (24) was not observed. Treatment of 4‐bromo‐5,6,7,8‐tetrahydro‐1‐naphthylamine (4) or of its 4‐chloro analogue 5 with amidosulfuric acid gave 1‐amino‐4‐bromo‐5,6,7,8‐tetrahydronaphthalene‐2‐sulfonic acid (9) and its 4‐chloro analogue 10, respectively, which were dehalogenated to 2. Preparations of 13 and 24 were achieved by sulfonation of 5‐nitro‐1,2,3,4‐tetrahydronaphthalene (14) and 6‐nitro‐1,2,3,4‐tetrahydronaphthalene (22) to 4‐nitro‐5,6,7,8‐tetrahydronaphthalene‐2‐sulfonic acid (15) and 3‐nitro‐5,6,7,8‐tetrahydronaphthalene‐1‐sulfonic acid (23), respectively, followed by Béchamp reductions. The sulfonic acid 13 was also obtained by hydrogenolysis of 4‐amino‐1‐bromo‐5,6,7,8‐tetrahydronaphthalene‐2‐sulfonic acid (11) or of its 1‐chloro analogue 12; compounds 11 and 12 were synthesized from N‐(4‐bromo‐5,6,7,8‐tetrahydro‐1‐naphthyl)acetamide (7) and from its 4‐chloro analogue 8, respectively, by sulfonation with oleum and subsequent hydrolysis. By ‘baking’ the hydrogensulfate salt of 1 or 20 compounds 3 and 21 were obtained, respectively. Synthesis of 16 was achieved by sulfur dioxide treatment of the diazonium chloride derived from 2‐nitro‐5,6,7,8‐tetrahydro‐1‐naphthylamine (17) giving 2‐nitro‐5,6,7,8‐tetrahydronaphthalene‐1‐sulfonyl chloride (18), followed by hydrolysis of 18 to the corresponding sulfonic acid 19 and final reduction.