The naturally occurring enediynes1 represent a novel class of antitumor antibiotics that feature a (Z)-hex-3-ene-1,5-diyne moiety constrained in a 9-or 10-membered ring. Coupled with other structural domains responsible for drug activation and delivery, the enediyne antitumor antibiotics present challenging targets for chemical synthesis.1a-c Stimulated by the intriguing mechanism of action and promising biological activity, extensive chemical and biological investigations on enediynes have been carried out during the past decade.1 It is known that cycloaromatization2 of enediynes such as 2 will give the diradical species 3, which can damage DNA through hydrogen atom abstraction from the deoxyribose residue (Scheme 1).1a,d,e,3 This event is regarded as the origin of the biological activity of enediynes. However, the extreme lability of simple 9- or 10-membered ring enediynes presents an obstacle for the development of synthetic enediyne drugs. In our recent work, we have established an efficient methodology for conversion of the thermally stable 1,2-diynyl-substituted allyl alcohols into acyclic enediynes by rearrangement of the allylic double bond.4 A relatively unstrained 11-membered ring enediyne was synthesized similarly.4b Our methodology is conceptually related to the intramolecular allylic rearrangement proposed for the action of artifacts of the maduropeptin chromophore5,6 and represents one of the emerging strategies7 for enediyne prodrug design and synthesis. In this paper, we disclose the synthesis and DNA cleavage activity of the 10-membered ring enediyne