Kinetics and mechanism of the ortho-Claisen rearrangement of allyloxynaphthoquinones

Abstract

The kinetics of the Claisen rearrangements of the allyloxynaphthoquinones (1)–(3) are reported for a range of solvents, and activation parameters are calculated for rearrangements in solvents of different types. The Claisen rearrangement in protic solvents is shown to differ in mechanism from that in aprotic solvents. The relative ease of the rearrangements of (1)–(3) is discussed in relation to earlier predictions, and a transition-state model suggested on the basis of the observed solvent and structure effects. These studies are of relevance to the problem of the Claisen rearrangement in biological systems, and suggest that caution should be exercised in the design and interpretation of biosynthetic experiments in this area.