Synthesis Of Bi-functional Triazolium Carbene Precursors And Their Application In The Asymmetric Silylation

In the study of organic chemistry,the formation of new C-C,C-Si,C-N,C-B is very important,especially catalysts are used for the reactions.The catalyst can make the reaction easier,more selective and environmentally friendly,and the use of highly catalysts can develop many new synthetic strategies.At the same time,catalyst was applied to classic reactions can also get surprising results.The asymmetric catalytic is the key of the research.Carbene is one of the most popular catalyst in the field of organic chemistry.Since the discovery of stable carbenes,carbenes have been widely used in asymmetric catalytic reactions.Compared with phosphine ligands and nitrogen-phosphorus ligands,carbine have a unique electronic effect,can be used in organic metal catalysis and organic catalysis.And triazole carbene is a widely used catalyst.Chiral catalysts contain at least one chiral element,and we bring the central chiral carbene into the[2.2]paracyclophane,resulting in a class of chiral ligands.The ligand can be used either in an organic catalytic reaction or in an organometallic catalytic reaction.Our group used the ligands to catalyze the boronization and silylation reactions of unsaturated carbonyl compounds to obtain good results.Water is one of the most abundant substance.When compared with organic solvents,water is cheap,not combustible and non-toxic.If the appropriate use of water as an organic solvent can bring many environmental benefits and unexpected results.And our previously synthesized ligands can not be used in the aqueous phase.Therefore,we would like to try to modify the previously synthesized triazole salts to obtain a bifunctional triazole salt and hope it can be used to asymmetric silylation reactions.This paper includes the following sections.1.Summarization of carbene catalysis and aqueous catalysisN-heterocyclic carbene(NHCs)have been widely used in organic synthesis since Bertrand et al reported a stable nucleophilic carbene.Carbene ligands can catalyze many reactions in combination with transition metals.Carbene ligands can catalyze reaction from benzoin condensation reaction to widespread used.The reaction in water or aqueous media can bring many benefits,because the product is less soluble in water,easier product separated,and water is a more secure reaction medium,can reduce costs.2.Synthesis of Bifunctional TriazoleThe diazonium salt was obtained by Sp-4-amino-12-bromo[2.2]paracyclophane and then reacted with LiBr to obtain Sp-4,12-dibromo[2.2]paracyclophane.Sp-4,12-dibromo[2.2]paracyclophane was reacted with benzophenone hydrazone to give Sp-4-benzophenone hydrazone-12-bromo[2.2]paracyclophane.And then SP-(4-N-formylbenzophenone hydrazone)-12-bromo[2.2]paracyclophane was obtain by formylation.The intermediate product was reacted with 2-hydroxybenzeneboronic acid obtain SP-N-formyl-N-{(2-hydroxyphenyl)[2.2]paracyclophan-12-yl}benzophenone hydrazone.HCl(aq)was added to obtain Sp-4-(2-hydroxyphenyl)-12-formohydrazino[2.2]paracyclophane hydrochloride.3.Asymmetric silylation of aromatic aldehydes catalyzed by bifunctional triazole salts(S,Sp)-3 can catalyze the silylation of aromatic aldehydes in the presence of water as the solvent and DBU as base.The optimum conditions for this reaction were screened to obtain the optimum reaction conditions.And under the conditions of the substrate development,found that for most of the aldehydes can be high yield and moderate er.Innovation1.We synthesized a series of novel bifunctional triazole carbenes based on[2.2]paracyclophane,and successfully introduced active groups on[2.2]paracyclophane.2.For the first time,carbene was used to catalyze the asymmetric silylation of aromatic aldehydes and achieved good yields and ee.3.The asymmetric silylation of aromatic aldehydes in the aqueous phase was achieved for the first time.