Reactions of Cyclic Diynes with Acceptor‐Substituted Alkynes: Syntheses of Doubly Bridged Dewar Benzenes

The reaction of the AlCl 3 complex of cyclic diynes (mainly a 14‐membered ring) with dimethyl acetylenedicarboxylate (DMAD) or bis( tert ‐butylsulfonyl)acetylene (BTSA) and related compounds was investigated. The reaction of the AlCl 3 complex of cyclotetradeca‐1,8‐diyne ( 1 , n = 5) with DMAD affords in 60% yield two isomers in a ratio of 7:3. The isomers were identified as the 1,4‐ and 2,3‐bridged Dewar benzene derivative A and the 1,2‐ and 3,4‐bridged Dewar benzene derivative B . Acetylenes with sterically more demanding groups such as BTSA or bis(diphenylphosphanyl)acetylene P , P ′‐dioxide (BDPA) yield only the isomer A . The X‐ray structures of the cycloadduct between 1 ( n = 5 and 6) and BTSA, as well as of 2,3‐bis( tert ‐butylsulfonyl)‐1,4,5,6‐tetramethylbicyclo[2.2.0]hexa‐2,5‐diene ( 31 ) are described. The mechanism of the cycloadditions is discussed.