37716-09-9Relevant academic research and scientific papers
Generation of N-Centered Radicals via a Photocatalytic Energy Transfer: Remote Double Functionalization of Arenes Facilitated by Singlet Oxygen
Soni, Vineet Kumar,Hwang, Ho Seong,Moon, Yu Kyung,Park, Sung-Woo,You, Youngmin,Cho, Eun Jin
, p. 10538 - 10545 (2019)
An unprecedented approach to the generation of an N-centered radical via a photocatalytic energy-transfer process from readily available heterocyclic precursors is reported, which is distinctive of the previous electron transfer approaches. In combination with singlet oxygen, the in-situ-generated nitrogen radical from the oxadiazoline substrate in the presence of fac-Ir(ppy)3 undergoes a selective ipso addition to arenes to furnish remotely double-functionalized spiro-azalactam products. The mechanistic studies provide compelling evidence that the catalytic cycle selects the energy-transfer pathway. A concurrent activation of molecular oxygen to generate singlet oxygen by energy transfer is also rationalized. Furthermore, the occurrence of the electron transfer phenomenon is excluded on the basis of the negative driving forces for one-electron transfer between oxadiazoline and the excited state of fac-Ir(ppy)3 with a consideration of their redox potentials. The necessity of singlet oxygen as well as the photoactivated oxadiazoline substrate is clearly supported by a series of controlled experiments. Density functional studies have also been carried out to support these observations. The scope of substrates is explored by synthesizing diversely functionalized cyclohexadienone moieties in view of their utility in complex organic syntheses and as potential targets in pharmacology.
Regioselectivity Associated with the 1,3-Dipolar Cycloaddition of Nitrones with Electron-Deficient Dipolarophiles
Padwa, Albert,Fisera, Lubor,Koehler, Konrad F.,Rodriguez, Augusto,Wong, George S. K.
, p. 276 - 281 (2007/10/02)
A study of the cycloaddition behavior of a series of electron-deficient dipolarophiles with C-aryl-N-alkylnitrones has been carried out.The 1,3-dipolar cycloaddition proceeds in high yield to produce isoxazolidines.This cycloaddition embodies a high degree of both regiochemical and stereochemical control and provides an efficient entry into such heterocyclic systems.The reactions follow frontier orbital predictions.Most dipolarophiles undergo cycloaddition to give 5-substituted isoxazolidines.The orientation has been explained in terms of maximum orbital overlap of the nitrone LUMO-dipolarophile HOMO.As the electron affinity of the dipolarophile increases, an increasing tendency toward formation of the 4-substituted isoxazolidine is encountered.In certain cases diastereomeric isoxazolidines were formed via different two-plane orientation complexes.The ratio of the diastereomers reflects the free energy difference of the two transition states.This difference comes from repulsive interactions caused by steric hindrance and attractive van der Waal forces associated with maximum ? overlap of the substituent groups.The transition state which dominates in a particular case will depend on the nature of the groups attached to the N atom of the nitrone and to the dipolarophile ? bond.
