The Development of Metal-free Visible Light Photochemistry and Computational Mechanism Studies on Visible Light Photocatalysis
Supervisor:cheng jin pei
The renaissance of long-thriving visible-light photochemistry in 2008 is mostly built on the numerous exciting achievements of photoredox catalysis for organic syntheses.Being a competitor against enzyme catalysis,transition-metal catalysis and organocatalysis,the photochemistry has come to the forefront in organic chemistry as a powerfull strategy for the activation of organic molecules under very mild conditions with a selective pattern.Especially,the emergence of oganophotocatalysis and external-photocatalyst-free photochemistry has attracted growing attention for their low-cost,no-residue-of-metal and easily up-scaling features,which is a paradigm of Green Chemistry.In contrast to the rapid development of photocatalytic reactions,however,the research on mechanisms and the origins of setereoselectivity in photo-induced asymmetric reactions is still in its infancy,confining the knowledge of the nature of photochemistry and the rational design of new photochemistry.To address these issues montioned above,this thesis aimed at the development of metal-free photochemistry as well as the computational studies on the origins of setereoselectivity in photo-induced asymmetric reactions.(1)A visible-light-induced,9,10-dicyanoanthracene catalyzed procedure for decarboxylative alkynylation of carboxylic acids was achieved.The reaction covered a broad scope of α-amino acids,α-oxo acids,and α-keto acids under very mild conditions,delivering alkynyl products in moderate to excellent yields.The feature of this methodology,that is the metal-free,optional-solar-light-driven,feasibly scaled-up,and synthetic-utility product,may make itself useful in organic synthesis and industry.(2)The discovery of radical reactivity for 3-aryl benzofuran-2(3H)-ones led to the novel oxidative amination of these compounds.The reaction scope is quite substantial,and a range of 3-arylbenzofuran-2(3H)-ones as well as oxindoles were tolerated,giving the corresponding amination products in moderate to high yields.Mechanism investigation indicated that the thermal activated rather than photo-induced electron-donor-acceptor complex is the key intermediate to triger a single-electron-transfer event.(3)The stereoselective origin of the photo-induced,asymmetric phase-transfer catalytic perfluoroalkylation of β-ketoesters was interpreted by density functional theory calculations.The selective attack of chiral ion pair by trifluoromethyl radical,which is formed by cinchoninum ion and enolate through the hydrongen bond and electrostatic interactions,it was believed,should be responsible for the high ena ntioselectivity.The idea that making quinoline ring more electron-deficient would improved enantioselectivity was achieved by the oxidation of quinoline nitrogen,which is confirmed by literature.These understandings will throw light on the design of novel phase-transfer catalysts and related reactions.