Studies On The Synthesis And Application Of POSS Supported Chiral Catalysts

Chiral imidazolinone and chiral diphenylprolinol trimethylsilyl ether have been widely used and got a in-depth development in asymmetric synthesis.Among the metal-free chiral organic catalysts,chiral imidazolinone plays a dominant role in asymmetric catalysis and can be well implemented in asymmetric Diels-Alder cycloaddition,asymmetric 1,3-dipolar cycloaddition,asymmetric Michael addition,asymmetric transfer-hydrogenation reaction etc.and chiral diphenylprolinol trimethylsilyl ether exerts an ideal effect on asymmetric Michael addition reaction,Mannich reaction,and asymmetric Aldol reactions.However,it is the difficulties in recycling and separating of small molecules prolinol silyl ether that restrict its practicability and hinder the development itself.In order to solve the problem of recycling chiral catalyst,human beings have used various of carriers to support small molecule chiral catalyst so as to separate product and catalysts by using the properties of carriers.POSS is a kind of cage silicone molecule nano-scale structure of its regular structural features and high thermal stability make it widely used in different fields.Generally,POSS have a good solubility in dichloromethane,chloroform,tetrahydrofuran,ethyl acetate and other solvents,but it is insoluble in n-pentane,n-hexane,diethyl ether,methyl t-butyl ether and high polarity methanol,DMF.So it is a class a good soluble carrier.Solubility differences with excellent catalytic performance and POSS-based chiral imidazolinone and chiral prolinol silicon ether characteristics,we design chiral imidazolinone and chiral prolinol ether-supported silicon onto POSS,and the use of POSS differences in solubility in different solvents,and after the reaction the catalyst is recovered by way of recrystallizationIn this article,POSS was as a carrier and chiral prolinol silicon ether and Chiral imidazolinone as catalysts,Catalysts was supported through Click reaction.Processes were as follows:1.chloropropyl trimethoxysilane is used as starting materials to synthesis eight chloropropyl of POSS(POSS-C1)by hydrolysis condensation,POSS-C1 and then with NaN3 nucleophilic substitution reaction octagonal POSS-N3,steps yield 19.0%;phenyltrimeth-oxysilane as a raw material obtained by hydrolysis-condensation containing seven uncapped phenyl POSS sodium salt,the sodium salt of POSS with 3-bromopropyl trichlorosilane"angle-cap" obtained containing phenyl and a seven-bromopropyl of POSS(single horn POSS-Br),a single horn POSS-Br and NaN3 nucleophilic substitution reaction to obtain a single horn POSS-N3,three steps in 35%yield;tyrosine methyl ester hydrochloride was synthesized from phenolic hydroxyl group of chiral imidazolidinone,reacted with 3-bromo-propyne introduced a triple bond;finally triple bond-containing chiral imidazolidinone respectively octagonal and single POSS-N3 angle POSS-N3 Click reaction performed,results showed that:with a chiral imidazolidinone octagonal POSS-N3 triple bond connection did not succeed,the resulting product is speculation that hindered too;and with the single horn POSS-N3 The reaction can be successful,a yield of 80%.the product was recrystallized from methyl-tert-butyl(MTBE).But the-supported chiral catalyst of instability easily decomposed in Ethyl acetate,methylene chloride,acetone,nitromethane solvent.2.With Boc-L-hydroxyproline-proline methyl ester by reaction with 3-bromo-propyne introduced a triple bond,a triple bond-containing and PhMgC1 proline methyl ester with the introduction of two phenyl Grignard reaction occurs,then with trimethylsilyl trifluoromethanesulfonate substitution reaction to obtain a triple bond small molecule chiral prolinol silicon-containing ethers,three steps yield 40%;and finally a triple bond-containing chiral prolinol silyl ether and single angle POSS-N3 reacte through Click reaction obtained POSS-supported chiral prolinol silicon ether,the product was recrystallized from methyl-tert-butyl,total yield 32%.3.The POSS-supported chiral prolinol silicon ether catalyst was applied to asymmetric Michael addition reactions of aldehydes and arylnitroalkenes,First step was to make propionaldehyde and trans-nitrostyrene react as a template,then optimize the conditions of reaction to obtain the optimum conditions for the catalyst(solvent:CH2Cl2,catalyst equivalent:20%mol,reaction temperature:10 ℃,reaction time:48 h),In this condition,implemented the catalyst to catalyze 13 substrates to obtain the prospective result of the reaction(yield 80-90%,dr value 82:18-92:8,ee 96->99%),Finally the catalyst can be simply recycled through recrystallization and recurrently used 8 times without significantly decrease in catalytic effect(yield 70-78%,dr value 86:14-92:8,ee 96-99%).4.By analyzing statistics of IR,1H NMR,13C NMR,29Si NMR,LC MS,final product’s structure was confirmed to match with the target’s.In summary,POSS-supported chiral prolinol silicon ether catalyst is an excellent catalytic effect when catalyzing the asymmetric Michael addition reactions of aldehydes and arylnitroalkenes.It is evident that the catalyst not only inherits the advantages of small molecules prolinol silicon ether,but also have characteristics of recovery and recycling.