Radical Boration Of Enamine Compounds

Radical reaction was widely applied to the synthesis of heterocyclic compounds due to the high reaction efficiency,excellent regional selectivity and good functional group compatibility.Compared with reactions based on carbon radicals,phosphorus radicals and nitrogen radicals,few boron radicals reactions was reported.As one of the precursors of boron radicals,the lewis base borane is mostly solid with an efficient and convenient synthesis approach and stable chemical properties.The boration reaction based on boron radicals has become one of the hotspots and attracted the attentions of many researchers.As an important method to synthesize organic borides,the traditional boration reaction of unsaturated hydrocarbons was usually carried out by a metal-catalyzed ionic reaction.In this thesis,the radical-based boration reaction of enamine was studied under metal-free catalysis,in which the NHC-borane is used as the radical precursor.The main work are as follows:A series of enamine esters,enamine nitriles,radical precursor NHC-borane and catalyst-2,4,6-triisopropyl thiol were designed and synthesized for the following boration reaction.As a template reaction,the boration reaction to(Z)-3-phenyl-3-phenyl amino-ethyl acrylate was studied and the?-boration product was obtained.The optimum conditions for efficient reaction involve use of triazole-BH₃,2,4,6-triisopropyl thiol and ACCN in acetonitrile as solvent.The results showed that this method have many advantages,good regioselectivity,excellent stereoselectivity,excellent substrate compatibility,better yields and dr parameter.The boration reaction of enamine nitrile was also explored and?-boronation product with higher yield was obtained too,but poor stereoselectivity hold us back.The stereochemistry and possible mechanism of the boration reaction were also discussed in this thesis and the trans-addition was proved by the configuration in the single crystal structure of compound 4k.The NHC-boryl radicals in boration reaction,initiated by ACCN,were added into the C=C of enamine esters to obtain the?-carbon radicals.And then a hydrogen atom of the mercaptan was captured by the intermediate to generate the boronated product and sulfur radicals.The new NHC-boryl radicals and thiol were produced finally by the reaction of the radical precursors and sulfur radicals.