The Cycloaddition Reactions of Some 7-Alkylidenecycloocta-1,3,5-trienes

A number of 7-alkylidenecycloocta-l, 3, 5-trienes, all unstable, yield novel π8+π2 cycloadducts with a range of π2-addends. The reactions of 7-methylenecycloocta-l, 3, 5-triene with ethene- tetracarbonitrile, 4-phenyl-l, 2, 4-triazoline-3, 5-dione, diethyl azodicarboxylate and chlorosul- fonyl isocyanate are described. The tetraene did not react with maleic anhydride or dimethyl acetylenedicarboxylate. As well, the reactions of l, 3, 5-trimethyl-7-methylenecycloocta-l, 3, 5- triene, 2, 9a-dihydro-lH-cyclopentacycloocteneand l, 2, 3, 10a-tetrahydrobenzocyclooctene with ethenetetracarbonitrile and of 7-isopropylidenecycloocta-l, 3, 5-triene with 4-phenyl-l, 2, 4- triazoline-3, 5-dione are discussed. The intermediacy of homotropylium zwitterions in the reactions is postulated.