Novel derivatives of ascomycin throught photochemistry

摘要

Irradiation of ascomycin 1 leads to three reaction pathways: (a) [1,3]-sigmatropic shift of the allylic carbonyl group leading to the ring-contracted products 3 and 4, (b) electron-transfer from the amide nitrogen to teh carbonyl group followed by reorganisation leading to a zwitterionic intermediate Z which undergoes either intramolecular cyclisation (leading to. 6 in CH_3CN) or addition of methanol (leading to 2 in MeOH), and (c) decarbonylative fragmentation resulting in the acyclic lactone 5.