Dehydration of hexacarbonyldicobalt protected tertiary propargylic alcohols. Stereo- and regiochemistry, synthesis of enantiomerically pure manicone and normanicone

Article abstract of DOI:10.1055/s-1991-26531

The stereochemistry and regiochemistry of the dehydration of hexacarbonyl-μ-[η-(3RS,5S)-(+)-3,5-dimethyl-1-heptyn-3-ol]dicobalt (Co-Co) and hexacarbonyl-μ-[η-(4RS,6S)-(+)-4,6-dimethyl-7-octyn-4-ol]dicobalt (Co-Co) with diethyl ether-boron trifluoride complex, trifluoroacetic acid or phosphorus(V) oxide have been investigated. The distribution of the isomeric products [(E)-enynes 41-86%, (Z)-enynes 9-59%, enynes with exomethylene group 0-9%] is dependent on the substrate structures as well as the nature of dehydrating agent: By acid-catalyzed hydration of the corresponding enynes enantiomerically pure (E,S)-(+)-4,6-dimethyl-4-octen-3-one (manicone) and (E,S)-(+)-3,5-dimethyl-3-hepten-2-one (normanicone) have been synthesized.