Very recently, a chromophore (1) of potent antitumor chromoprotein antibiotic, C-1027, as well as kedarcidin (2), has been disclosed to possess a highly strained bicyclo[7.3.0]dodecadiyne core structure. A strategy masking the 3-ene-1,5-diyne system 1 as 1,5-diyne 3 is a fascinating approach from the viewpoints of total synthesis and design of related DNA-cleaving molecules. We developed a general and efficient route for the 9-membered cyclic diyne system through an intramolecular acetylide addition mediated by Li(TMS)_2/CeCl_3, from a precursor such as 8 possessing a conformationally not rigid C4-C5 single bond. Futhermore, we found that the cyclic 1,5-diyne system such as bicyclo[7.3.0]dodeca-2,6-diyn-11-ene 11 undergoes an unprecedentedly facile Cope rearrangement below room temperature, although its isomeric bicyclo[7.3.0]dodeca-2,6-diyn-12- enes 21 and 23 do not. Thus, the delicate supression of Cope rearrangement of 9-membered cyclic 1,5-diyne system has been attained by a subtle remote structural change. In addition, we report stereocontrolled synthesis and the abusolute configuration of the sugar moiety.
