Reduction of the 1,2,5‐thiadiazole ring of 3,6:12,15‐di‐1,4‐benzo[6.6](3,4)‐1,2,5‐thiadiazolo‐ and 3,5:11,13‐di‐1,3‐benzo‐[6.6](3,4)‐1,2,5‐thiadiazolocyclophanes. Selective preparation of cis ‐ and trans ‐[2 3 ]cyclophane‐1,2‐diacetoamide

The effect of the [2.2.2]cyclophane ring structure on the reduction of 1,2,5‐thiadiazole ring incorporated in cyclophanes 1a‐c and 2a‐c was investigated. When reduced by sodium metal in ethanol followed by acetylation, para[2 3 ]cyclophane 1 gave a mixture of the expected cis‐ and trans ‐diamides, 3 and 4 , in which 4 was the major product. On the other hand, reduction of 1 with lithium aluminum hydride proceeded in a cis ‐selective manner and gave 3 as a major product after a treatment of the reduced products with acetic anhydride. The reduction of metacyclophane 2 , which is less strained than 1 , proceeded exclusively in cis ‐fashion and a subsequent treatment of the reduction product with acetic anhydride gave only cis ‐diamide 6 .