Addition to Acetylenic Bonds of Carbon-Centered Radicals

Intramolecular Addition to Acetylenic Bonds of Carbon-Centered Radicals 

Hence cyclization is selective toward the (Cy5) compound in the Cy5/Cy6 case and toward the (Cy7) compound in the Cy6/Cy7 case. In spite of these promising results, the scope of the reaction and the origin of a selectivity different from that observed when the same stabilized radicals add to double bonds have not been studied. 

Electroreductive cyclization of acetylenic halides has been extensively studied by Peters, particularly in the case of 6-halo-l-phenyl-l-hexyne. A complicated scheme was proposed for the 6-chloro compound to explain the results. The origin of the cyclized products may be sought among others in the radical formed by direct reduction of the carbon-halogen bond. Another possibility is the reduction of the carbon-carbon triple bond (already recognized previously in the reductive cyclization of bis-propargylamines ) 

In conclusion, it appears that in spite of the reservations made in the Introduction, the intramolecular addition of carbon-centered radicals to triple bonds is an efficient process in the Cy5/Cy6 case, less efficient in the Cy6/Cy7 case, and does not work with the lower homologs. The selectivity is very high toward the (Cy5) compound in the Cy5/Cy6 case, and toward the (Cy6) com- 

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