Furanmonogones A (1) and B (2), two rearranged acylphloroglucinols with an unprecedented 4,5-seco-3(2H)-furanone skeleton, were isolated from the flowers of Hypericum monogynum. Their structures were established based on 1D- and 2D-NMR data, quantum chemical predictions (QCP) of ¹³C NMR chemical shifts, and electronic circular dichroism (ECD) calculations. Baeyer–Villiger oxidation at the single bond (C4–C5) of the acylphloroglucinol core was proposed as a key step in the plausible biogenetic pathway of 1 and 2.