Total synthesis of halicholactone and neohalicholactone

The total synthesis of the marine natural products neohalicholactone (1) and halicholactone (2), in enantiomerically pure form, are reported. Key steps in the synthesis of each compound include a cis-selective Wittig reaction, stereoselective cyclopropanation, nine-membered lactone formation using the Yamaguchi method and late-stage stereoselective Cr(II)/Ni(II) mediated coupling of vinyl iodides 39 and 50 with aldehyde 14. In the case of the neohalicholactone synthesis the two major components which were coupled in this convergent synthesis were each derived from the enantiomers of commercially available malic acid. The synthesis served to confirm the original assignment of absolute configuration which was made by Yamada and Clardy. We also demonstrated, through the preparation of diastereoisomers, that another reported compound closely related to neohalicholactone is likely to be the C-15 epimer 67.