In contrast to the corresponding compounds lacking alkoxy substituents, the 2-benzopyran-3-ones 5, 6, 7 and 9 are stable and easily isolated. In contrast to the 6-methoxy derivative 7, the 7-methoxy isomer 8 cannot be isolated; the stabilising effect of the 6,7-methylenedioxy group in 5 and 9 is therefore due to the alkoxy group at C-6. This is consistent with a donor-acceptor interaction involving the C-6 alkoxy group and the pyrone carbonyl which decreases reactivity towards nucleophilic attack by water.