A Short Synthesis of (R,R)‐(‐)‐Pyrenophorin from ( S )‐Propylene Oxide and a 3‐Pentenoic Acid d 5 ‐Reagent

Analysis of the known syntheses of pyrenophorin ( 1 ) (Scheme 1) reveals that they all rest upon the use of reagents with d 1 ‐, d 3 ‐, or a 2 ‐reactivity umpolung for the establishment of at least one of the 1,4‐distances of functional groups. A different approach, outlined in Scheme 2, has now been realized: the non‐conjugated and the conjugated 7‐hydroxyoctenoic acids 10 and 11 , obtained from dienone dianion derivatives of type 3 and d,l ‐ or ( S )‐methyloxirane, are converted to the macrodiolides 12 and 13 , respectively. These are directly oxidized with introduction of an oxygen function at position 4 , see 13 → 1 and 12 → 16 → 17 → 1 . The overall transformation of the γ,δ‐unsaturated ketone 18 to pyrenophorin ( 1 ) in 27% yield takes six steps, partly without purification of intermediates.