Abstract
The title compounds were synthesized from their possible biogenetic precursors through hydroperoxide intermediates generated by photo-oxygenation. This route for biological oxygenation may serve as a substitute to epoxidation. The
13
C n.m.r. spectral assignments for all intermediates were made. Single-crystal
X
-ray analyses unequivocally established the 1
S
configuration in dihydrochrysanolide (14) and its hydroperoxy-analogue (12). Isomorphous crystals of (12) and (14) belong to the monoclinic system, space group
P
2
1
, with
a
= 14.350(6),
b
= 5.882(3),
c
= 10.343(3)Å, β= 107.64(2)°,
Z
= 2, for (12), and
a
= 14.461(6),
b
= 5.887(3),
c
= 9.698(4)Å, β= 107.44(2)°,
Z
= 2, for (14). Least-squares refinement of atomic parameters converged to
R
0.040 for (12) and 0.033 for (14) over 1 484 and 1 300 reflections, respectively, measured by diffractometer.