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-member ed ring) with dimethyl acetylene dicarboxylate (DMAD) or bis(tert-buty lsulfonyl)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 isom ers were identified as the 1,4- and 2,3-bridged Dewar benzene derivati ve A and the 1,2- and 3,4-bridged Dewar benzene derivative B. Acetylen es with sterically more demanding groups such as BTSA or bis(diphenylp hosphanyl)acetylene P,P'-dioxide (BDPA) yield only the isomer A. The X -ray structures of the cycloadduct between I (n = 5 and 6) and BTSA, a s well as of l)-1,4,5,6-tetramethylbicyclo[2.2.0]hexa-2,5-diene (31) a re described. The mechanism of the cycloadditions is discussed.