New NMR signals
were observed at d 5.68 (s, H-5) and d 1.92 (m, 2H-3a) consistent
with those reported for the 3-peroxy derivative of pseudopyronine
B.18 This instability should not be observed if the
4-hydroxyl group is trapped as the methyl ether. Indeed,
4-O-methyl pseudopyronine A (12), prepared in 53% yield
from 1 by reaction with excess trimethylphosphate, was stable
in CDCl3 for many weeks with no observed degradation.