卤代酮的合成.docx
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卤代酮的合成
经典化学合成反应标准操作
目录
1.前言2
2.直接卤化2
3.经重氮酮制备4
4.从weinreb酰胺制备6
5.傅克酰基化合成卤代酮7
6其他合成α-卤代酮的方法9
1.前言
α-卤代酮的合成广泛应用于现代有机合成中,多用于溴的烷基化、合成咪唑及噻唑等杂环类化合物,其合成方法常用直接卤化、经重氮酮制备、经Weinreb酰胺制备、傅克酰基化等方法合成。
2.直接卤化
酮的α-氢易被取代,可以直接合成α-卤代酮。
一般操作是将酮与卤素于醋酸、氯仿、DMF或水中反应。
除卤素外,硫酰氯、五卤化磷、过溴化吡啶氢溴酸盐(C5H5NH.Br3)、三卤化三甲基苄基铵盐等也可以做卤化试剂。
对称酮或只有一个取代方向的酮卤代时,可以良好产率(80~90%)生成α-卤代酮。
不对称酮卤代,往往生成α-及α’-卤代酮的混合物。
由于酮卤代的决定步骤是酮的烯醇化,因此,易形成烯醇的方向优先卤代。
例2-甲基环己酮与亚硫酰氯作用,多取代的α-氢优先氯代。
若利用双(二甲基乙酰胺基)三溴化氢做溴化剂,可使不对称酮在少取代一边溴代。
若将不对称酮首先转变成为一定构型的烯醇盐,继而卤代,是区域定向卤代的新方法。
另外,甲基酮可用甲基格式试剂与相应的Weinreb酰胺来制备,如下例即是先合成甲基酮,后溴化来合成α-溴代酮的。
合成实例一
Asuspensionofketone2A(700mg,2.17mmol)inaceticacid(15ml)washeatedto70℃,followedbyadditionofbromine(347mg,2.17mmol).Afterthemixturewasstirredat70℃for3h,thesolventwasevaporatedandtheresiduewaspurifiedbycolumnchromatographytogivethecompound2B(591mg,68%).
合成实例二
Bromine(7.99g,50mmol)inCHCl3(20ml)wasaddedinadropwisemannertoastirredsolutionof2,5-dimethoxy-4-bromoacetophenone2C(12.95g,40mmol)inCHCl3(100ml)at5℃.Aftertheadditionwascompleted,thereactionmixturewasallowedtowarmtoroomtemperatureandstirredforanadditional2h.Themixturewaspouredontocrushedice,theorganicportionwasseparatedandwashedwithwater,saturatedNaHCO3solution,andagainwithwater.ThesolutionwasdriedMgSO4,andevaporatedtodrynessunderreducedpressuretogiveacrudeproduct.TheproductwasrecrystallizedfromMeOHtoyield14.70g(87%)ofthedesiredbromoacetophenone2Dasawhitesolid.
合成实例三
Toasolutionof1-(2-aminopyrimidin-4yl)ethanone(412mg,3mmol)inglacialaceticacid(1mL)and48%aq.HBr(0.3mL),bromine(0.153mL)inaceticacid(0.4mL)wasaddedandtheresultingorangesolutionwasstirredatRTfor1.5hours.Afterdilutingwithethylacetate(15mL),theprecipitatewasfilteredandwashedwithethlacetatethusaffordingthetargetcompoundasawhitishsolid(580mg,65%).
合成实例四
Benzyltrimethylammoniumtribromide(4.17g,10.7mmol)wasaddedtoasolutionofCompound2E(4.00g,10.7mmol)inCH2Cl2-MeOH(5:
2,25mL).ThemixturewasstirredatRTfor3h.AtthistimethereactionmixturewasconcentratedinvacuoandH2O(15mL)wasadded.Themixturewasextractedwithdiethylether(3×20mL).Thecombinedorganicextractswerewashedwithbrine(15mL),driedoverMgSO4,filteredandconcentratedinvacuo.Theresiduewaspurifiedbysilicagelchromatography(hexanes:
EtOAc,3:
1)toaffordtoaffordCompound2F(3.97g,8.8mmol,82%)asathickyellowoil.
3.经重氮酮制备
不对称酮卤代时,有时无法得到单卤代产物。
此时,从酰氯或活泼酯经重氮酮合成α-卤代酮可以顺利得到单卤代产物。
重氮酮常用重氮甲烷的醚溶液加到相应的酰氯或活波酯中制得,也可以用三甲基硅重氮甲烷处理相应的酰氯制得。
重氮酮用相应的卤化氢处理即可高产率得到α-卤代酮。
合成实例一
Toasolutionofcompound3A(0.7g,4.3mmol)inDCM(15ml,2dropsofDMF)wasaddedoxalylchloride(0.55ml,6.47mmol).ThereactionmixturewasstirredatRTfor10min,atrefluxfor1h.Thenthesolventwasremovedinvacuo.TheresiduewasdissolvedinTHF(8ml),thenthemixturewascooledto0℃.Diazomethaneinether(42ml,21mmol)wasthenaddedslowly,thereactionsolutionwasstirredat0℃for1h,followedby2hatRT.Thereactionmixturewascooledto0℃again,and1.2mlof35%ofHBrinaceticacidwasaddedslowly.ThereactionmixturewasstirredatRTovernight.Thereactionsolutionwaspouredintocooledwater,andextractedwithEtOAc.Theorganiclayerwaswashedwithwater,saturatedammoniumchlorideandbrine,driedoversodiumsulfate.Thesolventwasconcentratedunderreducedpressuretoafford1gofα-bromoketone3B(yield80%).
Note:
Preparationofdiazomethane
Areactionanddistillationapparatusisassembledbyconnectinganadditionfunnelandcondensortoa100mllong-neckdistillationflask.Twoinseriesreceivingflasksareconnectedtotheapparatuswiththesecondflaskcontaininganinductiontube.Asolutioncontaining6gpotassiumhydroxidein10mlwater,andasolutioncontaining35mlCarbitol(diethyleneglycolmonoethylether)and10mlofetherareplacedinthedistillationflask.20~30mletherisplacedinthesecondreceivingflaskmakingsuretheinductiontubeisimmersedintotheether.Bothreceivingflasksarecooledto0℃.Asolutioncontainingp-toluenesulfonyl-N-methyl-N-nitosamide(21.5g,0.1mol)in140mletherisplacedintheadditionfunnel.Heatthedistillationflaskto70℃inawarmwaterbath.Astheetherbeginstoboil,startaddingthep-toluenesulfonyl-N-methyl–N-nitrosamidesolutiondropwiseovera20minuteperiod.Swirldistillationflaskfromtimetotime.About3gofdiazomethane(0.07mol)isdissolvedinetherdistillate.Thereagentshouldbeusedatoncewithoutstoringit.
合成实例二
(Trimethylsilyl)-diazomethane(34ml,67mmol,20Msolutioninhexanes)wasaddeddropwisetoasolutionofethylsuccinylchloride(5g,303mmol)inacetonitrile(60ml)overaperiodof30minafterthemixturewasstirredfor2h,hydrogenbromide(14ml,30%solutioninaceticacid)wasslowlyaddedover15minafterthereactionwasstirredforanadditional1h,thesolventwasevaporatedundervacuum.Theresiduewasdissolvedinethylacetateandwashedwith1NNaOHandbrine.Theorganiclayerwasdriedwithsodiumsulfate,filtered,andevaporatedundervacuumtoyield4.3g(64%)ofethyl5-bromo-4-oxopentanoate
4.从weinreb酰胺制备
N-甲氧基-N-甲基酰胺做为易离去基团,可因与有机金属试剂在温和的条件下反应,以良好的收率生成酮。
若以N-甲氧基-N-甲基-2-卤乙酰胺与有机金属试剂作用就可以良好收率得到α-卤代酮。
N-甲氧基-N-甲基-2-卤乙酰胺很容易由相应的卤乙酰卤与N-甲氧基-N-甲基氯化铵反应得到。
合成实例一
Benzylmagnesiumchloride(1.0Mindiethylether,50.0mL)wastreatedwith2-chloro-N-methoxy-N-methylacetamide(5.16g,37.5mmol)inTHF(200mL)at-78℃dropwise.Thereactionwasallowedtowarmslowlytoroomtemperatureovernightandquenchedwith1Nhydrochloricacid.Thelayerswereseparatedandtheorganicphasedried(Na2SO4),filtered,andthefiltratewasconcentratedunderreducedpressure.Theresiduewaspurifiedbyflashcolumnchromatography(silicagel,elutionwithhexanes)toprovidethetitlecompound.
合成实例二
Toastirredsolutionof3-phenylsydnone
(1)(0.25g,1.54mmol)indryTHF(100ml)at-78℃underanatmosphereofdrynitrogengaswasaddedN,N,N’,N’-tetramethylethylenediamine(0.29ml,1.93mmol)thenn-butyllithium(2.31ml,3.47mmol,15Minpentane)dropwise.After0.5h,theappropriate2-chloro-N-methoxy-N-methylacetamide(1.93mmol)wasaddedtothegoldenyellowsolutionand,afteraadditional1h,themixturewasquenchedwithaqueoushydrochloricacid(100ml,10%v/v)thenextractedwithdichloromethane(3*100ml).thecombinedorganiclayersweredried(MgSO4)andthesolventremovedinvacuotoaffordthecorrespondingo-acylatedsydnone4asanoilwhichwaspuriiedbycolumchromatographytoaffordcolorlesscrystals.Yield86%.
5.傅克酰基化合成卤代酮
与芳烃直接相连的α-卤代酮,可以从卤乙酰卤与相应芳烃经傅克酰基化合成α-卤代酮。
此类方法多以三氯化铝做催化剂,在适宜的温度下反应合成α-卤代酮。
但该方法后处理较为困难,且收率一般。
合成实例一
Bromoacetylchloride(28.2g,180mmol)inCH2Cl2(60mL)wasaddeddropwisetoacooledsolution(-10℃)of1-phenyloctane5(34.2g,180mmol)andAlCl3(24.0g,180mmol)inCH2Cl2(50mL).ThesolutionwasthenallowedtoreturntoRTandstirredforafurther3h.Themixturewaspouredslowlyontoice(100g),theaqueousphasewasextractedwithCH2Cl2(60mL)andtheorganicphaseswerecollected,dried(MgSO4)andconcentrated.Theproductwascrystallisedtwice(CH3OH:
H2O)togive6(38.3g,68%)aswhitecrystals.
合成实例二
Toamixtureofoftetraphenylmethane(1;3.20g,10.0mmol),AcCl(4.00g,51.0mmol)andCS2(50mL)wasaddedAlCl3(6.70g,50.3mmol)andthereactionmixturewasrefluxedfor18h.Aftercoolingtor.t.,theCS2wasdecantedandtheresiduewasmixedwithice(100g),conc.HCl(37%,25mL),andCH2Cl2(100mL).Thismixturewasstirreduntiltheprecipitateshadcompletelydissolved.Theorganiclayerwasdried(Na2SO4),filteredandthesolventwasremovedinvacuo.Afterchromatographyonsilicagel(acetonehexanes)4.82g(99%)of4awasobtainedasacolorlessresin.
合成实例三
ToasolutionofAlCl3(1.73g,13mmol)innitromethane(4mL)wasaddedchloroacetylchloride(0.25mL,3.1mmol)andasolutionof6(510mg,2.6mmol)innitromethane(4mL)at0°C.Theice-waterbathwasremoved5minlaterandthemixturewasallowedtowarmuptoRT.Thestirringwascontinuedforanadditional2h.Themixturewasthenquenchedwithice-coldaq1MHCl(50mL),extractedwithCH2Cl2(5*20mL),andthecombinedorganicextractswerewashedwithbrine(2*15mL)untilneutralanddried(Na2SO4).Completeremovalofthesolventinvacuobelow40℃(CAUTION!
itromethanemayexplodeifheated)followedbyFC(hexane–EtOAc,2:
1)affordedpure7asawhitesolid;yield:
455mg(64%);mp129–131°C(toluene).
6其他合成α-卤代酮的方法
除了上述四种常用的合成α-卤代酮方法外,不对称酮的直接卤化受到区域选择性不高的限制。
为了克服这个缺点,可先将不对称酮转化成相应的烯醇异构体,然后再进行卤化反应,则可达到提高区选择性α-卤代的目的。
常用的卤化剂为卤素、N-卤代酰胺等。
例如,化合物6A采用NBS在dioxane中加热反应,能得到良好收率α-溴代酮,但应用NCS的效果较差。
另外,烯醇硅烷醚可和卤素直接反应,如6C在低温下溴化,能得到收率很高的相应α-溴代酮。
其机理如下:
烯醇硅烷醚也可与硫酰氟氯反应高收率地得到α-氯代酮,如还庚酮烯醇硅醚的氯代反应。
合成实例一
N-Bromosuccinimide(0.377g,2.13mmol)wasaddedallatoncetoasolutionofmethyl4-acetamido-3-chloro-6-(1-ethoxyvinyl)pyridine-2-carboxylate(0.636g,2.13mmol)inTHF(40mL)andwater(2mL)atroomtemperature.After15minutes,thereactionmixturewasconcentratedandtheresiduepartitionedbetweendichloromethaneandwater.Theorganiclayerwasseparated,dried(MgSO4),andconcentratedtoprovidemethyl4-acetamido-3-chloro-6-(bromoacetyl)pyridine-2-carboxylate(0.714g,2.04mmol).1HNMR(CDCl3):
9.12(s,1H),7.99(br.s,1H),4.82(s,2H),4.06(s,3H),2.36(s,3H).
合成实例二
2-Acetylpyrimidine(7.37g,60.4mmol)andDIEA(23.4g,181.2mmol)weredissolvedindryCH2Cl2underN2,andthencooledinanicebath.TIPS-triflate(17.9