Medium-sized cyclophanes—XVII : Tetra-, hexa-, octa- and decahydropyrenes from [2.2]metacyclophane. Transannular dehydrogenation,isomerization, and disproportionation reactions by means of benzoyl peroxide,metal salts and sulfuric acids

[2.2]Metacyclophane (1) undergoes a variety of reactions according to the reagents and conditions. These include (1) substitution (path a), (2) transannular dehydrogenation (path b and c), (3) cycloisomerization (path d) and (4) transannular hydrogenation. A brief summary of these reactions is presented.The diversity of the reactions of 1 is further explored using benzoyl peroxide (BPO), cupric chloride, aluminum chloride, other metal salts, H₂SO₄ and FSO₃H. With BPO or cupric chloride, one-electron transfer mechanism is postulated. This involves a tautomeric ion pair formed by the intramolecular arylation with an aryl cation radical. A supporting evidence in favor of the mechanism is presented from experiments using various metal salts in different solvents.On the contrary, the reaction with aluminum chloride gives decahydropyrene (8) and octahydropyrene (11) together with cycloisomerization product 5 and dehydrogenation products 2, 3 and 4. When treated with AlCl₃HCl 1 gives similar products as above but the product ratios are quite different. The major product is 5 but only a trace amount of 8 is formed. The reaction with H₂SO₄ or FSO₃H also produce 2, 4, 5 and 11. Some mechanistic evidence in favor of the disproportionation reaction is presented.