35 プロスタグランジンの合成

抄録

The construction of the ω-side chain in prostaglandins was mostly achieved so far by the C-C bond forming reactions such as the Wittig condensation of an aldehyde with a phosphorane, or the Michael addition of an organocuprate to a cyclopentenone. We report here a new route to prostaglandins via a fulvene with a side chain of a ω-side chain equivalent. Reaction of cyclopentadiene with 3,3-ethylenedioxyoctanal (7) in the presence of an anion-exchange resin (Amberlite IRA-400) gave 6-(2,2-ethylenedioxyheptyl)fulvene (8). The Diels-Alder adduct (9) of the fulvene with α-chloroacrylonitrile gave 7-anti-(3-oxo-1-trans-octenyl)-5-chloro-5-cyanobicyclo[2.2.1]heptene (15) by the treatment with an acid, which is reported as an intermediate of 12-epiprostaglandins. On the other hand, the Diels-Alder adduct (11) of the fulvene with α-chloroacryloyl chloride was derived to 7-(3,3-ethylenedioxyoctylidene)bicyclo[2.2.1]heptenone (10). The acid catalyzed reaction of 10 gave a mixture (6:4) of 7-anti- and 7-syn-(3-oxo-1-trans-octenyl)bicyclo[2.2.1]heptenone (16 and 17). The later compound was subjected to the Baeyer-Villiger oxidation to give lactone 18, followed by the iodolactonization, acetylation and reduction to yield cyclopentanolactone 20, which is reported as an intermediate of natural prostaglandins.