Carpe diene ! Europium-catalyzed [3,3] and [5,5] rearrangements of aryl-pentadienyl ethers.

A general protocol for the europium-catalyzed rearrangement of aryl-pentadienyl-ethers is described. The mode of rearrangement and product formation in this reaction was solely determined by the aryl substituent para to the phenol. If the para -position is occupied by a substituent, the substrate undergoes a [3,3] rearrangement to the ortho -position to form a prochiral branched diene. In turn, a free para -position in the starting material allows the reaction to proceed via a [5,5] rearrangement and leads to a linear conjugated diene product. The severely underdeveloped and synthetically valuable [5,5] rearrangement was investigated in terms of scope and mechanism.