7-endo Selective Aryl Radical Cyclization onto Enamides Leading to 3-Benzazepines: Concise Construction of a Cephalotaxine Skeleton
摘要:
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.
predominantly gave 6-endo cyclization products. These results suggest that the exo or endo selectivity of radicalcyclizationonto the alkenic bond of enamides can be controlled by positional change of the carbonyl group. For an understanding of these selectivities, heat of formation for each transition state was calculated. 6-endo-Selective radicalcyclization was applied to the radical cascade, enabling
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.