Pentadienyl radical, cyclization

The pentadienyl radical formed from piperylene is known to cyclize at 650°C to cyclopentene and cyclopentadiene although, according to an esr study, this isomerization is not observed between -130 and -hl80°C. A lower temperature (210°C) is sufficient to give cyclized products (Scheme 131) from the radical 343 which is assumed to form by cyclization of radical 342, when the peroxyacetate 341 is thermolyzed, but the yield of cyclized products is less than 10%. ... 

Activated copper powder or copper(II) acetylacetonate were effective catalysts in the pyrolytic cyclization of 2-azido-3-(2,4-pentadienyl)-l,4-quinones to benzopyrolizines 17 by the presumed intermediacy of a copper(II)-nitrene species which adds to the diene by a radical pathway. Although the yields were generally low, complete regioselectivity and diastereoselectivity (simple and substrate induced) were observed152. 

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