Asymmetric Total Syntheses and Structure Confirmation of Chlorofucins and Bromofucins.

Substrate-controlled asymmetric total syntheses and structure confirmation of (+)-(3E)- and (-)-(3Z)-chlorofucin [(E)-1a and (Z)-1a], and (+)-(3E)- and (-)-(3Z)-bromofucin [(E)-1b and (Z)-1b] were accomplished. Our syntheses feature as key steps haloetherification (either conventional' or one-pot organoselenium-mediated') of ,-trans-,-unsaturated oxocene alcohol 9 and our (E)- and (Z)-selective cross-metathesis (CM) protocols. More importantly, a rationale is provided for the strikingly different pathways followed by ,-trans-,-unsaturated oxocene alcohol 9 and its ,-cis isomer 9 in the presence of different electrophiles during the intramolecular electrophilic addition reactions.