20.500.12556/RUL-165184 Photocatalyst-free wavelength-dependant sequential ring transformations of pyrazolo[1,2-a]pyrazolones We report sequential wavelength-selective photochemical transformations of 1-alkenylpyrazolo[1,2-a]pyrazolones to pyrazolo[1,2-a][1,2]diazepines or cyclobuta[c]pyrazolo[1,2-a]pyrazolones. Irradiation of 1-alkenylpyrazolo[1,2-a]pyrazolones with visible-light (blue LED, 457 nm) induced selective ‘ring switching’ transformation into pyrazolo[1,2-a][1,2]diazepines, which underwent electrocyclisation yielding cyclobuta[c]pyrazolo[1,2-a]pyrazolones upon irradiation with UV A light (black LED, 365 nm). Due to the very narrow irradiation wavelength now available from OLED sources, the selective formation of either 5,7-bicyclic or 5,5,4-tricyclic ring systems from the 5,5-bicyclic starting material is possible by changing the wavelength of the irradiation source. The transformations took place under mild conditions in the absence of additives or photocatalysts. Mechanistic studies indicate that these transformations proceed through the formation of an excited triplet state of the substrate, followed by selective homolytic C(1) N(8) bond cleavage, intersystem crossing, and cyclization of the zwitterionic intermediate on the ground potential energy surface. The subsequent photoinduced disrotatory stereospecific 4π-electrocyclization of the 5,7-bicyclic systems leads to 3D-rich 5,5,4-tricyclic products. C-N bond cleavage heterocycles visible-light ring transformation photocatalyst-free transformations cepitev C-N vezi heterocikli vidna svetloba pretvorbe obročev pretvorbe brez katalizatorja true false true Angleški jezik Slovenski jezik Članek v reviji 2024-11-26 13:29:24 2024-11-26 13:29:26 2024-11-27 03:50:48 0000-00-00 00:00:00 2024 0 0 Str. 4441-4451 iss. 21 Vol. 366 5 Nov. 2024 0000-00-00 Zaloznikova Objavljeno NiDoloceno 0000-00-00 0000-00-00 0000-00-00 547.77:544.52 1615-4169 10.1002/adsc.202400684 209299715 Adv_Synth_Catal_-_2024_-_Kulasic_-_Photocatalyst‐Free_Wavelength‐Dependant_Sequential_Ring_Transformations_of_Pyrazolo_1.pdf Adv_Synth_Catal_-_2024_-_Kulasic_-_Photocatalyst‐Free_Wavelength‐Dependant_Sequential_Ring_Transformations_of_Pyrazolo_1.pdf 1 86C219D3F83CCC3E8E7391625DAB167C 3dc5e413dae7c71b1a52576533b5c3c701256c702d3f6f1da9c4ea198f0f3654 e5233f84-abf1-11ef-b232-0050569b8976 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=196193 https://onlinelibrary.wiley.com/doi/10.1002/adsc.202400684 1 aa27b5ab-abf1-11ef-b232-0050569b8976 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=196192 Fakulteta za kemijo in kemijsko tehnologijo 0 0 0