An efficient new synthesis has been elaborated for non-natural (−)-dactylolide ((−)-2) and its 13-desmethylene analogue 4, employing a HWE-based macrocyclization approach with β-keto-phosphonate/aldehyde 19 and the respective 13-desmethylene derivative as the key intermediates. Both (−)-2 and 4 as well as the corresponding C20 alcohols inhibit human cancer cell proliferation with IC50 values in the