In the course of detailed analysis of the chemical constituents of Atalantia monophylla Correh, a new acridone base, C24H27NO4 (M+ 393), has been isolated. The structure of this alkaloid has been established and is reported in the present communication. Balaban, Mikai, and Nenitzescu showed that reaction of 2,4,6-trimethylpyryllium perchlorate with sodium borohydride gave two products to which they assigned the structures 2 and 4 (stereochemistry not given). They made the reasonable assumption that 4 was formed by a rapid valence isomerization from 3. Because of our general interest in electrocyclic reactions, we investigated this reaction somewhat more thoroughly than had the previous workers. The reaction proceeds exactly as they described and the two products were isolated in good yield. The nmr spectra are in accord with the assigned structures. In addition the spectrum of 4 permits us to assign its stereochemistry: the Δ5 double bond must be trans (J5,6 = 15.0 Hz) and the Δ3 double bond is cis. We showed the presence of transient intermediate 3 via spectral means (uv at 277 nm, nmr at -22°C) and estimated the rate of conversion of 3 to 4 (first-order, k ~3×10⁻⁴ sec⁻¹ at 13°C).