Pigments of Fungi. Part 70.* Total Synthesis of (R)-Semixanthomegnin and the X-Ray Crystal Structure of (±)-7-Chloro-10-methoxy-3-methyl-3, 4-dihydro-1 H-naphtho[2,3-c]pyran-1,6,9-trione

Abstract

(R)-Semixanthomegnin (8), which has been converted by others to the mould metabolite (3R,3′ R)-xanthomegnin (9), is prepared in seven steps from (R)-propylene oxide (16). A single-crystal X-ray structure analysis of (±)-7-chloro-10-methoxy-3-methyl-3,4-dihydro-1H-naphtho[2,3-c]pyran-1,6,9-trione (25) confirms the regiochemistry of the cycloaddition reaction between 2,5-dichloro-1,4-benzoquinone and the new, highly oxygenated, chiral butadiene derivative (2).