Radical Oxidative Cross-couplings With Alkynes And Alkenes

Over the past few years,radical involved cross-coupling has emerged as an efficient alternative approach for the construction of C-C/C-X bonds besides traditional organometallic pathway.Generally,radicals with a single electron have a strong tendency to form chemical bonds.Since it is too difficult to control the reaction selectivity of radicals,selective bond formation from radical intermediates has been less developed compared with that from ionic intermediates.In this thesis,an introduction to the features of the generation and reaction of free radicals was given at first.Research development of the direct C-H functionalization of alkenes or alkynes through radical cross-coupling was then reviewed.Our research started from the existing problems and challenges in radical cross-couplings with alkenes and alkynes.The main results of this thesis are as follows:1.A general and vesatile method for the direct C(sp3)-C(sp)cross-coupling with terminal alkynes has been developed.Alkyl radicals generated from different approaches were able to couple with terminal alkynes by judicious selection of the catalyst combination.The reaction protocol is complementary to the traditional Sonogashira coupling for the synthesis of substituted alkynes.Mechanistically,the reaction was found to go through a radical reaction pathway and synergistic cooperation of the metal catalysts was the key for controlling the reaction selectivity.2.A novel zinc-catalyzed reaction system for the oxidative cross-coupling between aldehydes and terminal alkynes.A good reaction selectivity was achieved,even with 1:1 ratio of terminal alkyne and aldehyde.This reaction protocol provides an atom economic way for the synthesis of ynones.3.An iodide-catalysed radical oxidative alkenylation of sulfonyl hydrazides with simple alkenes was developed for the synthesis of alkenyl sulfones.Mechanistic insight revealed that catalytic HI elimination was quite similar to the β-hydride elimination of transition metals for alkenyl functionality recovery.4.By utilizing I2 and peroxides as the catalyst and oxidant combination,(3+2)oxidative annulation between β-keto esters/2-pyridinyl-β-esters and alkenes/alkynes was achieved for the synthesis of dihydrofurans,furans and indolizines.A novel N-iodosuccinimide-mediated decarboxylative(4+1)oxidative annulation between 2-vinylpyridine derivatives and malonate monoesters was developed.