Selective reduction of the 5-carbomethoxy- and the 5-carbethoxy-4-hydroxy-2H-pyran-2-one derivatives (5a approximately 11, 19) to yield the 5-hydroxymethyl derivatives (12 approximately 18) was accomplished using 1.1 mol equivalent of borane-methyl sulfide complex. Additionally, reduction of the 3-acetyl-4-hydroxy-2H-pyran-2-one derivatives (23, 26 and 29) with borane-methyl sulfide complex afforded the binary condensed pyrone derivatives (25, 28 and 3 1) in good yields.
Total Synthesis of Islandic Acid I Methyl Ester, Rosellisin and Rosellisin Aldehyde
Total synthesis of islandic acid I methyl ester (2), rosellisin (3) and rosellisin aldehyde (4) has been accomplished starting from 4-hydroxy-5-hydroxymethyl-6-methyl-2H-pyran-2-one (9a) via formylation of 9a with dichloromethyl methyl ether and titanium tetrachloride as a key step.