A synthesis of allylic difluorides is described, exemplified by the preparation of the title compound, which was shown to elicit the biological responses characteristic of (Z)-8-dodecenyl acetate, the pheromone of the Oriental fruit moth. It is concluded that the geometry of the double bond rather than its chemical reactivity is essential for biological activity.
Many insect pheromones contain double and triple bonds as an essential feature of their structure.
1 We recently reported on a general synthesis of (Z,Z)-3,3-difluoro-1,4-dienes and acetylenes in connection with the synthesis of fluorinated arachidonic acids. 2 It occurred to us that some of that methodology could also be utilized for the synthesis of allylic difluoromonoenes, thereby affording the opportunity to prepare pheromones in which a methylene group o to the double bond is replaced by a CF2 group. No such methodology was available prior to this work. Such substitution would have no significant effect on the geometry of the pheromone, yet exert a pronounced influence on the reactivity of the double bond with the potential of altering the interaction of the pheromone with its exquisitely sensitive receptor. The biological consequences of such a change in structure were sufficiently intriguing to test this concept. Other investigators 394 have prepared and tested fluorinated pheromones, in which fluorine is substituted at vinylic carbons. We chose to synthesize (Z)-lO,lO-difluoro-8-dodecenyl acetate (z), the difluoro-analog of the pheromone of the oriental fruit moth, Qapholita molesta, whose behavioral responses to the pheromone have been studied in depth.' 1-Bromo-l,l-difluoro-2-hexyne (L) was prepared' from 1-pentynyl lithium and CF2BrCl as a difficultly separable mixture containing 10% of 1-bromo-1-pentyne, which was directly converted to the l-iodide 1_with sodium iodide in refluxing methyl ethyl ketone for 20 hours. Fractional distillation (b.p. 85" at 65
Torr.) gave the pure iodide (z)6 in 62% yield. Radical addition7 of 2 (5.7 mmole) to 5hexen-l-01 acetate (12.2 mmole) in benzene (1 ml) with AIBN (0.12 mmole) in a sealed tube at