In addition to the differences in the activation barriers, there are some differences in the relative stability of Int-4 and Int-6 for 2-methylthiophene and 2-methylfuran. For the 2-methylthiophene, the C-H activation product Int-4 is the most stable species (Gº298K = +2.2 kcal mol -1 ) whereas for the 2methylfuran the ring-expanded C-O functionalisation product is more stable (Gº298K = -14.0 kcal mol -1 ). The model suggests that the reaction of 1 and thiophene derivatives under the Pd catalytic conditions is likely to proceed through the C-H alumination pathway to form the C2-aluminated thiophenes and that, unlike furans, ring expansion should not be observed with this system.