The reactivity difference between class 1 and class 2 substrates can be illustrated by reaction progress curves with 1a (class 1) and 1p (class 2) as substrates under the standard thermal conditions (o-DCB, 120 °C). While the reaction with 1a proceeds cleanly to afford almost quantitative conversion to 6a (via MOP ether 4a and enol ether 5a), with 1p, the reaction gives successively 4p and then the enol ether 5p, but its conversion to 6p is slow under these conditions (Scheme 6). Scheme 5. Substrate Scope of the Ketone Claisen Rearrangement Under Microwave Conditions. Scheme 6. Reaction progress curves for the reactions with 1a and 1p.