VITAMIN-B12, A CATALYST IN THE SYNTHESIS OF PROSTAGLANDINS

A prostaglandin F2α precursor containing all structural features from C6 to C20 with 8R, 9S, 11R and 12R chirality is obtained by the one step formation of two C-C bonds in the B12-catalyzed radical cyclization-addition sequence starting from a chiral cyclopentene bromoacetal and l-octyne-3-one. The B12-catalyzed radical cyclization-elimination sequence of a chiral cyclopentene precursor leads to (-)-(3aR,6aS)-3,3a,6,6a-tetrahydro-2H-cyclopenta abfuran-2-one. Its (+)-(3aS,6aR-enantiomer is obtained via B12-catalyzed, enantio- selective isomerization of cyclopentene oxide to (R)-2-cyclopentene-l-ol followed by the B12-catalyzed radical cyclization-elimination sequence of its bromoacetal. © 1990.