Figure 3: Overview of the synthetic route from bipinnatin J (1) to intricarene (4) and hydroxy cyclopentenone 11.
(a) Attempted synthesis of the bielschowskysin skeleton via conjugate addition of water and photochemical interception of the presumed intermediate. Conversion of bipinnatin J (1) to its methyl ether 8 via SN1 reaction was followed by oxidative cleavage of the furan ring to yield diene dione 8. Conjugate addition of water was supposed to yield 9 and enable a photochemical [2+2] cycloaddition to form the central four-membered ring of bielschowskysin. (b) Unexpected formation of intricarene (4) and hydroxy cyclopentenone 11 under photochemical conditions. (c) Synthesis of acetate 12 and diene-dione 13 and failure to yield intricarene under identical photochemical conditions.
