Synthesis and characterization of representative octa-1,3,5,7-tetraenes and deca-1,3,5,7,9-pentaenes
Several representative conjugated linear tetraenes and pentaenes were prepared by a variety of synthetic methods including Wittig condensation, 1,8-Diazabicyclo[5.4.0]undec-7-ene(DBU)-induced dehydrobromination, and Hofmann elimination. For the preparation of (E,E)- and (Z,E)-octa-1,3,5,7-tetraene, the Hofmann elimination sequence is by far the most convenient method of synthesis, while DBU-induced dehydrobromination of (E,E)-4bromonona-1,5,7-triene produces excellent yields of (E,E,E,)- and 3Z,5E,7E)-nona-1,3,5,7-tetraene. Deca1,3,5,7,9-pentaene can be produced by several methods, but not in high yield. Undeca-1,3,5,7,9-pentaene and trideca-1,3,5,7,9,11-hexaene can also be prepared in low yield by the Wittig reaction. All the polyenes produced in this study polymerize rapidly in the crystalline state.