Synthesis Of Tri- And Tetraynes Using A Butadiynyl Synthon

摘要

Using a one-pot protocol, triynes and tetraynes are formed from the reaction of a dibromovinyl triflate and a terminal alkyne under palladium-catalyzed cross-coupling conditions.rnConjugated polyynes are useful building blocks for conjugated structures, and they show significant potential for new optical materials. They are also commonly isolated as natural products with significant biological activity. While the conjugated acetylenic framework of an unsymmetrical 1,3-diyne can be formed through a plethora of different transformations, that of 1,3,5-hexatriyne is typically more difficult to achieve. Two methods are commonly employed, the Cadiot-Chodkiewicz coupling and the Fritsch-Buttenberg-Wiechell (FBW) rearrangement, while other protocols also exist. To broaden the scope of the FBW rearrangement toward polyyne formation, the use of vinyl triflate 1 as a butadiynyl synthon was explored," and a general method was sought toward the formation of 1,1-dibromoolefins 2 (Scheme 1). In the course of subjecting 1 to Sonogashira coupling conditions in the presence of a terminal alkyne, we have discovered that the product of the reaction was not the expected olefin 2, but rather the triyne 3. It was immediately clear that this transformation offered a route to polyynes not accessible though a typical elimination reaction because the formation of 3 did not require the use of a strong base. Herein, the results of an initial study to optimize this protocol are presented.