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

The reaction of the AlCl3 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 AlCl3 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. Reactions of Cyclic Diynes with Acceptor‐Substituted Alkynes: Syntheses of Doubly Bridged Dewar Benzenes