THERMIC TRANSFORMATION OF PHENYL-PENTA-2,4-DIENYLETHERS INTO 4-(PENTA-2,4-DIENYL)-PHENOLS AS AN EXAMPLE FOR (5,5)-SIGMATROPIC REARRANGEMENTS . PRELIMINARY COMMUNICATION

The reaction between phenol and trans penta‐2,4‐dienyl chloride gave trans penta‐2,4‐dienyl Phenyl ether (I), whereas with a mixture of sorbyl chloride and 1‐methylpenta‐2,4‐dienyl chloride, pure trans, trans hexa‐2,4‐dienyl phenyl ether (IV) and trans 1‐methylpenta‐2,4‐dienyl phenyl ether (V) were obtained. The ether I gave, on heating in dilute solution at 185°, 4‐(penta‐2,4‐dienyl)‐phenol (III) as the main product, and also some 2‐(2‐vinylallyl)‐phenol (II). The ether IV provided, on heating at 165°, in addition to the ortho CLAISEN rearrangement product VI, mainly a mixture consisting of 94% 4‐(1‐methylpenta‐2,4‐dienyl)‐phenol (VIII) and only 6% 4‐(hexa‐2,4‐dineyl)‐phenol(IX). The latter product (IX) was the only para isomer produced on heating ether V, but in addition 22% of the ortho rearrangement product VII was formed. The migrations I → III, IV → VIII, and V → IX, proceeding through a ten membered transition state, are the first [5,5] sigmatropic rearrangements described. Copyright © 1968 Verlag GmbH & Co. KGaA, Weinheim