3-Phenyl-l,5-hexadiene

Phenyl-l,5-hexadiene (25 g) is heated under nitrogen at 176-178° for 26 h. Distillation through a Widmer column then gives almost pure 1-phenyl-1,5-hexadiene (18 g, 72%), b.p. 102.5-103.5°/8 mm.157... 

The first example of VA( )-catalyzed Cope rearrangement is shown in Scheme The treatment of 2-methyl-3-phenyl-l,5-hexadiene 7 with 6% PdCl2(PhCN)2 in THF at room temperature (r.t.) produced a 93 7 mixture of the rearranged dienes 8 and 9 in 87% yield. In contrast, the thermal Cope rearrangement of the diene 7 required elevated temperature (ti/2 = 13 h at 177 °C) and proceeded with less stereoselectivity, to yield a 3 1 mixture of 8 and 9. There are significant structural limitations to the PdCl2(PhCN)2-catalyzed Cope rearrangement under these conditions. 

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