Isagarin (1) was synthesized in four steps from 1,4-dimethoxynaphthaldehyde
(4). The key intermediate 2-(1,2-dihydroxyethyl)-1,4-naphthoquinon (3) was
found to react with acylated pyridinium ylides to afford, after spontaneou
s intramolecular condensation, the desired natural product isagarin (1). De
pending on the type of acylated pyridinium ylides, different types of new p
yranonaphthoquinone derivatives were obtained.