Radical-mediated 5-exo Addition/Cyclization Of Alkynoates And The DFT Mechanism Study

In this thesis, the synthesis of 3-sulfonated-4-arylcoumarins through the radical-mediated 5-exo addition/cyclization of alkynoates with sulfonylhydrazides is developed. The reaction mechanism of alkynoates with sulfonylhydrazides, H-phosphonate and arylaldehydes is studied with density functional theory(DFT) calculations. The main obtained results are shown as bellows:1. A facile and efficient 5-exo addition/cyclization of alkynoates with sulfonylhydrazides has been realized under metal-free conditions. The structures of the target products are confirmed by 2D NMR. Substituents at the para-position of phenoxy ring gave the C7-substituted 3-sulfonated coumarin. Using substrate with a methyl group and tert-buthyl at the meta-position of the phenoxy ring, the steric hindrance of the groups was found. Unexpectedly, a opposite ratio of regioisomers was observed from the reaction with 4-chloro-3-methylphenyl 3-phenylpropiolate. The results indicated that the steric hindrance of methyl group was not the main factor of the ratio of regioisomers.2. The molecular structures of products, obtained through the radical-mediated 5-exo addition/cyclization of alkynoates with sulfonylhydrazides, were confirmed by 2D NMR spectra and single-crystal X-ray diffraction analysis.3. The results of controlled experiments indicated that the reaction was achieved via a radical process, and the C-H bond cleavage would not be rate-limiting in the overall process. The DFT calculations indicated that the mechanism of radical-mediated addition/cyclization of alkynoates with H-phosphonates, arylaldehydes and sulfonylhydrazines might be 5-exo cyclization followed by 1,4-aryl migration process.