Biogenetic-type synthesis of santonin, chrysanolide, dihydrochrysanolide, tulirinol, arbusculin-C, tanacetin, and artemin

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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 13C n.m.r. spectral assignments for all intermediates were made. Single-crystal X-ray analyses unequivocally established the 1S configuration in dihydrochrysanolide (14) and its hydroperoxy-analogue (12). Isomorphous crystals of (12) and (14) belong to the monoclinic system, space group P21, 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.