Bu3SnH-mediated radical cyclizations of 2-(2-bromophenyl)-N-ethenylacetamide gave 6-exo cyclization product 15 as the major product, whereas N-[2-(2-bromophenyl)ethyl]-N-ethenylamides gave almost exclusively 7-endo cyclization products. These results indicated that the position of the carbonyl group on enamide played an important role in deciding the course of the cyclization. The 7-endo selective cyclization was applied to concise construction of a cephalotaxine skeleton.

No abstract

___A radical cascade involving 6-endo cyclization of aryl radicals generated fromfollowed by 5-endo-trig cyclization of the resulting α-amidoyl radicals afforded phenanthroindolizidines bearing a methyl substituent at the angular C13a position. 2,3,6-Trimethoxy derivative was synthesized by using this method, but its spectral data were not in accord with those of literature values reported for hypoestestatin 1. Further synthetic study towards hypoestestatin 1 is demonstrated. _______________________________________________________________________________________

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