Abstract
The structure of the ethyl ester, C18H22O8, m.p. 116°, which was obtained from O, O-diacetylusnic acid by the ozonolysis followed by alcoholysis was established by infrared spectral analyses as being ethyl 2-(2-hydroxy-3-acetyl-5-methyl-4, 6-diacetoxy-phenyl)-propionate (VI). An alternative possible structure of usnic acid (IV) has therefore been excluded, and the structure of usnic acid (III) has been confirmed. The behaviors of lactone A, m.p. 132°, an ozonolytic product of O, O-diacetylusnic acid was reexamined. It was proved by infrared and nuclear magnetic resonance spectra, that reacetylation of deacetyl-lactone A with acetic anhydride and pyridine was affected at the 3-position of 2-coumaranone ring to furnish lactone B, m.p. 132°. Acetylating with acetic anhydride and conc. H2SO4, lactone A was regenerated from deacetyllactone A. Thus the earlier conclusions concerning with the lactones A and B have been corrected.
