Undeca-3,5-diyn

Scheme 6.62 The 3<52-pyran derivative 288 as a possible intermediate in the thermal cyclization of undeca-3,8-diyne-2,10-dione (287).

Corey reported a racemic synthesis of 11,12-LTA4 beginning with undeca-2,5-diyn-l-ol and forming the racemic epoxy aldehyde 28 (Scheme 4.11) The remainder of the synthesis parallels his approach to LTA4. 

Polyacetylenes and vinyl acetylenes are known to show some selectivity in their reactions [109, 110]. Raphael [111] showed that terminal acetylenes could be protected as their sodium salts during reduction of disubstituted acetylenes using sodium in liquid ammonia. This procedure enabled him to reduce a disubstituted acetylenic bond in the presence of a terminal acetylene in the stereospecific synthesis of trans-undeca-7-en-l-yne (18) from undeca-l,7-diyne (19). This method of protection of monosubstituted acetylenes was used during reduction of the enone system (20) with lithium in liquid ammonia [112]. Raphael made a study of other possible methods of protecting terminal acetylenes and found that the best of these was the bromoacetylene [113]. 

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