1、Organic ChemistryAlkynesNomenclatureuIUPAC:use the infix-to show the presence of a carbon-carbon triple bonduCommon names:prefix the substituents on the triple bond to the word“acetylene”Common name:Common name:IUPAC name:IUPAC name:D D imethylacetyleneimethylacetyleneV V inylacetyleneinylacetylene2
2、-Butyne2-Butyne1-Buten-3-yne1-Buten-3-yne1 11 1,6 6-H H e ep pt ta ad di iy yn ne e3 3-M M e et th hy yl l-1 1-b bu ut ty yn ne e6 6,6 6-D D i im m e et th hy yl l-3 3-h he ep pt ty yn ne e2 23 34 41 12 23 34 45 56 61 12 23 34 45 56 67 77 7CycloalkynesuCyclononyne is the smallest cycloalkyne isolate
3、d it is quite unstable and polymerizes at room temp the C-C-C bond angle about the triple bond is approximately 155,indicating high angle strainC C y yc cl lo on no on ny yn ne ePhysical PropertiesuSimilar to alkanes and alkenes of comparable molecular weight and carbon skeleton0.7660.766174174-36-3
4、60.7460.746125125-79-790.7160.7167171-132-1320.6900.6904040-90-900.6910.6912727-32-32(a gas)(a gas)8 8-126-126(a gas)(a gas)-23-23-102-102(a gas)(a gas)-84-84-81-81D ensityD ensityat 20Cat 20C(g/m L)(g/m L)Boiling Boiling PointPoint(C)(C)M eltingM eltingPointPoint(C)(C)Form ulaForm ulaN am eN am e1-
5、D ecyne1-D ecyne1-O ctyne1-O ctyne1-H exyne1-H exyne1-Pentyne1-Pentyne2-Butyne2-Butyne1-Butyne1-ButyneP PropyneropyneE EthynethyneH H C CC C H HC C H H3 3C CC C H HC C H H3 3C CC C C C H H3 3C C H H3 3(C C H H2 2)2 2C CC C H HC C H H3 3C C H H2 2C CC C H HC C H H3 3(C C H H2 2)3 3C CC C H HC C H H3
6、3(C C H H2 2)5 5C CC C H HC C H H3 3(C C H H2 2)7 7C CC C H HAcidityuThe pKa of acetylene and terminal alkynes is approximately 25,which makes them stronger acids than ammonia but weaker acids than alcohols(Section 4.1)terminal alkynes react with sodium amide to form alkyne anions N NH H2 2H H-C CC
7、C-H HH H-C CC C:-N N H H3 3+p pK Ka a 3 38 8(W W e ea ak ke er r a ac ci id d)p pK Ka a 2 25 5(S St tr ro on ng ge er r a ac ci id d)+Acidity terminal alkynes can also be converted to alkyne anions by reaction with sodium hydride or lithium diisopropylamide(LDA)because water is a stronger acid than
8、terminal alkynes,hydroxide ion is not a strong enough base to convert a terminal alkyne to an alkyne anionN N a a+H H (C CH H3 3)2 2C CH H 2 2N N L Li i+S So od di iu um m h hy yd dr ri id de eL Li it th hi iu um m d di ii is so op pr ro op py yl la am m i id de e (L LD D A A)K Ke eq q =1 10 0-9 9.3
9、 3p pK Ka a 1 15 5.7 7p pK Ka a 2 25 5-+(S St tr ro on ng ge er r a ac ci i d d)W W(e ea ak ke er r a ac ci id d)H HC CC CH HH H C CC CO O H HH H2 2O OAlkylation of Alkyne AnionsuAlkyne anions are both strong bases and good nucleophilesuThey participate in reactions with alkyl halides to form new C-
10、C bonds to alkyl groups;they undergo because alkyne anions are also strong bases,alkylation is practical only with methyl and 1 halides with 2 and 3 halides,elimination is the major reactionH HC CC CH HH HC CC C-N N a a+H HB Br rS So od di iu um m a ac ce et ty yl li id de eB Br ro om m o o-c cy yc
11、cl lo oh he ex xa an ne eA A c ce et ty yl le en ne e C C y yc cl lo oh he ex xe en ne eN N a a+B Br r -+e el li im m i in n-a at ti io on n(C C h h 9 9)Alkylation of Alkyne Anions alkylation of alkyne anions is the most convenient method for the synthesis of terminal alkynes alkylation can be repea
12、ted and a terminal alkyne can be converted to an internal alkyneH HC C C C -N Na a+B Br rN N a a+B Br r-S So od di iu um ma ac ce et ty yl l i id de e+1 1-B Br ro om m o ob bu ut ta an ne e1 1-H H e ex xy yn ne eC CH H3 3C CH H2 2C CC C-N Na a+C CH H3 3C CH H2 2C CC CC CH H2 2C CH H3 3C CH H3 3C CH
13、H2 2-B Br rN N a a+B Br r-+B Br ro om m o oe et th ha an ne e3 3-H H e ex xy yn ne e+S So od di iu um m b bu ut ty yn ni id de ePreparation from AlkenesuTreatment of a vicinal dibromoalkane with two moles of base,most commonly sodium amide,results in two successive reactions(removal of H and X from
14、adjacent carbons)and formation of an alkyneC CH H3 3C CH H=C CH HC CH H3 3C CH H3 3C CH H-C CH HC CH H3 3B Br r B Br rC CH H2 2C Cl l2 2B Br r2 22 2N N a aN NH H2 2N N H H3 3(l l)C CH H3 3C CC CC CH H3 32 2N Na aB Br r2 2N NH H3 32 2-B Bu ut te en ne e+-3 33 3o oC C2 2-B Bu ut ty yn ne eS So od di i
15、u um ma am m i id de e+Preparation from Alkenes for a terminal alkene to a terminal alkyne,3 moles of base are requiredC C H H3 3(C C H H2 2)3 3C C H H=C CH H2 2B B r r2 2C C H H3 3(C C H H2 2)3 3C C H H-C C H H2 23 3 N N a aN N H H2 2H H2 2O OC C H H3 3(C C H H2 2)3 3C C C C H H1-H exene1-H exene1,
16、2-D ibrom ohexane1,2-D ibrom ohexane1-H exyne1-H exyneC C H H3 3(C C H H2 2)3 3C C C C-N N a a+Sodium salt of 1-hexyneSodium salt of 1-hexyne-2 2 H H B Br rB B r r B B r rPreparation from Alkenes a side product may be an,a compound containing adjacent carbon-carbon double bonds,C=C=CA haloalkeneA ha
17、loalkene(a vinylic halide)(a vinylic halide)An alleneAn alleneAn alkyneAn alkyneRCC CRRHRH X HNaNH2RC C=CR-HBrC C CRRRHAllene a compound containing a C=C=C group the simplest allene is 1,2-propadiene,commonly named alleneAllenes most allenes are less stable than their isomeric alkynes,and are genera
18、lly only minor products in alkyne-forming dehydrohalogenation reactionsC CH H2 2=C C=C CH H2 2C CH H2 2=C C=C CH HC CH H3 3C CH H3 3C CC CH HC CH H3 3C CC CC CH H3 3 H H0 0 =-1 16 6.7 7 k kJ J (-4 4.0 0 k kc ca al l)/m m o ol lD DH H0 0 =-6 6.7 7 k kJ J (-1 1.6 6 k kc ca al l)/m m o ol lAddition of
19、X2uAlkynes add one mole of bromine to give a dibromoalkene addition shows anti stereoselectivityC CH H3 3C CC CC CH H3 3B Br r2 2C CH H3 3C CO O O OH H,L Li i B Br rC CC CB Br rH H3 3C CB Br rC CH H3 3a an nt t i i a ad dd di it ti io on n(E E)-2 2,3 3-D D i ib br ro om m o o-2 2-b bu ut te en ne e2
20、 2-B Bu ut ty yn ne e+Addition of X2 the intermediate in bromination of an alkyne is a bridged bromonium ionC CC CH H3 3C CC C H H3 3B Br rB Br rC CC CB Br rH H3 3C CC CH H3 3C CC CB Br rH H3 3C CC CH H3 3B Br rH H3 3C CC CC CB Br rB Br rC CH H3 3Addition of HXuAlkynes undergo regioselective additio
21、n of either 1 or 2 moles of HX,depending on the ratios in which the alkyne and halogen acid are mixed2,2-Dibromopropane2,2-Dibromopropane2-Bromopropene2-BromopropenePropynePropyneCH3C CHBrBrBrHBrCH3C=CH2CH3CCH3HBrAddition of HX the intermediate in addition of HX is a 2 vinylic carbocation reaction o
22、f the vinylic cation(an electrophile)with halide ion(a nucleophile)gives the productC CH H3 3C CC CH HH H-B Br rC CH H3 3C C=C CH H2 2B Br rA A 2 2 v vi i n ny yl li ic cc ca ar rb bo oc ca at ti io on n+C CH H3 3C C=C CH H2 2B Br rB Br rC CH H3 3C C=C CH H2 2+2 2-B Br ro om m o op pr ro op pe en ne
23、 eC CH H3 3C C=C CH H2 2B Br rB Br rC CH H3 3C C=C CH H2 2+Addition of HX in the addition of the second mole of HX,Step 1 is reaction of the electron pair of the remaining pi bond with HBr to form a carbocation of the two possible carbocations,the favored one is the resonance-stabilized 2 carbocatio
24、n+H HB Br rB Br rC CH H2 2C CH H3 3C CH HC CH H2 2C CH H3 3C CB Br rB Br rH HC CH H3 3C CC CH H2 2C CH H2 2C CH H3 3C CB Br rH HB Br rB Br rB Br rC CH H3 3C CC CH H3 3R R e es so on na an nc ce e-s st ta ab bi il li iz ze ed d 2 2 c ca ar rb bo oc ca at ti io on ns sl lo ow w e er rf fa as st te er
25、r1 1 C C a ar rb bo oc ca at t i io on n+HydroborationuAddition of borane to an internal alkyne gives a trialkenylborane addition is syn stereoselectiveB BH H3 3T TH H F FB BR RR R3 3-H H e ex xy yn ne e+A A t tr ri ia al lk ke en ny yl lb bo or ra an ne e(R R =c ci is s-3 3-h he ex xe en ny yl l g
26、gr ro ou up p)H HHydroboration to prevent dihydroboration with terminal alkynes,it is necessary to use a sterically hindered dialkylborane,such as(sia)2BH treatment of a terminal alkyne with(sia)2BH results in stereoselective and regioselective hydroborationB B-H HD D i i-s se ec c-i is so oa am m y
27、 yl lb bo or ra an ne e (s si ia a)2 2B BH H (s si ia a)2 2B BH H+1 1-O O c ct ty yn ne eA An n a al lk ke en ny yl lb bo or ra an ne eB B(s si ia a)2 2H HH HHydroborationuTreating an alkenylborane with H2O2 in aqueous NaOH gives an enol a compound containing an OH group on one carbon of a carbon-ca
28、rbon double bond an enol is in equilibrium with a keto form by migration of a hydrogen from oxygen to carbon and the double bond from C=C to C=O keto forms generally predominate at equilibrium keto and enol forms are and their interconversion is called 1 1.B B H H3 32 2.H H2 2O O2 2,N N a aO O H H2
29、2-B Bu ut ty yn ne e2 2-B Bu ut te en n-2 2-o ol l(a an n e en no ol l)2 2-B Bu ut ta an no on ne e(a a k ke et to on ne e)K Ke eq q =6 6.7 7 x x 1 10 06 6(f fo or r k ke et to o-e en no ol lt ta au ut to om m e er ri is sm m)H HO O H HO OHydroboration hydroboration/oxidation of an internal alkyne g
30、ives a ketone hydroboration/oxidation of a terminal alkyne gives an aldehyde3-Hexanone3-Hexanone3-Hexyne3-Hexyne1.BH32.H2O2,NaOHO1 1-O O c ct ty yn ne eA A n n e en no ol lH HH HO O H H2 2.H H2 2O O2 2,N N a aO O H H1 1.(s si i a a)2 2B B H HH HO OO O c ct ta an na al lAddition of H2O:hydrationuIn t
31、he presence of sulfuric acid and Hg(II)salts,alkynes undergo addition of water+PropanonePropanone(Acetone)(Acetone)1-Propen-2-ol1-Propen-2-ol(an enol)(an enol)PropynePropyneCH3C CHOHOHgSO4H2SO4H2OCH3C=CH2CH3CCH3Addition of H2O:hydration Step 1:attack of Hg2+(an electrophile)on the triple bond(a nucl
32、eophile)gives a bridged mercurinium ion Step 2:attack of water(a nucleophile)on the bridged mercurinium ion intermediate(an electrophile)opens the three-membered ringC CC CH Hg g+H HH H3 3C CO OH HH H+C CC CH Hg g+H H3 3C CH H+O OH HH HAddition of H2O:hydration Step 3:proton transfer to solvent give
33、s an organomercury enol Step 4:tautomerism of the enol gives the keto formC CC CH Hg g+H HH H3 3C CO OH HH H+O OH HH HC CC CH Hg g+H HH H3 3C CO OH HH H3 3O O+C CH H3 3-C C-C CH H2 2-H Hg g+O OE En no ol l f fo or rm mK K e et to o f fo or rm mC CC CH HO OH H3 3C CH H g g+H HAddition of H2O:hydratio
34、n Step 5:proton transfer to the carbonyl oxygen gives an oxonium ion Steps 6 and 7:loss of Hg2+gives an enol;tautomerism of the enol gives the ketoneH H2 2O O:C CH H3 3-C C-C CH H2 2-H H g g+O OO OH HH HH H+C CH H3 3-C C-C CH H2 2-H H g g+O OH H+C CH H3 3-C C-C CH H2 2-H H g g+O OH HHg2+CH3-C=CH2OHC
35、H3-C-CH3O+(e en no ol l f fo or rm m)(K K e et to o f fo or rm m)ReductionuTreatment of an alkyne with hydrogen in the presence of a transition metal catalyst,most commonly Pd,Pt,or Ni,converts the alkyne to an alkane2 2-B Bu ut ty yn ne eB Bu ut ta an ne e+C C H H3 3C C C C C C H H3 3P Pd d,P Pt t,
36、o or r N N i i2 2 H H2 2C C H H3 3C C H H2 2C C H H2 2C C H H3 33 3 a at tm mReductionuWith the Lindlar catalyst,reduction stops at addition of one mole of H2 this reduction shows syn stereoselectivityC CH H3 3C CC CC CH H3 3H H2 2C CC CC CH H3 3H H3 3C CH HH HL Li in nd dl la ar rc ca at ta al ly y
37、s st tc ci is s-2 2-B Bu ut te en ne e+2 2-B Bu ut ty yn ne eHydroboration-ProtonolysisuAddition of borane to an internal alkyne gives a trialkenylborane addition is syn stereoselective treatment of a trialkenylborane with acetic acid results in stereoselective replacement of B by HB BH H3 3T TH H F
38、 FB BR RR R3 3-H H e ex xy yn ne e+A A t tr ri ia al lk ke en ny yl lb bo or ra an ne e(R R =c ci is s-3 3-h he ex xe en ny yl l g gr ro ou up p)H HB BR RR RH H3 3C CH H3 3C CO O H HO OH HH H(C CH H3 3C CO O O O)3 3B Bc ci is s-3 3-H H e ex xe en ne e+A A t tr ri ia al lk ke en ny yl lb bo or ra an
39、ne e+Dissolving Metal ReductionuReduction of an alkyne with Na or Li in liquid ammonia converts an alkyne to an alkene with anti stereoselectivityR R R R2 2N Na a2 2N N a aN NH H3 3(l l)N N H H3 3(l l)R RR R H HH HH HH H2 2N Na aN NH H2 2t tr ra an ns s-4 4-O O c ct te en ne e4 4-O O c ct ty yn ne e
40、+Dissolving Metal Reduction Step 1:a one-electron reduction of the alkyne gives a radical anion Step 2:the alkenyl radical anion(a very strong base)abstracts a proton from ammonia(a very weak acid).R R-C CC C-R R+N N a a+N N a a+A An n a al lk ke en ny yl l r ra ad di ic ca al l a an ni io on nR R-C
41、 CC C-R R.:R R-C CC C-R RH HN NH HH HR RC CC CR RH HN NH HH H+A A n n a al lk ke en ny yl lr ra ad di ic ca al l+A A m m i id de ei io on n Dissolving Metal Reduction Step 3:a second one-electron reduction gives an alkenyl anion this step establishes the configuration of the alkene a trans alkenyl a
42、nion is more stable than its cis isomer Step 4:a second acid-base reaction gives the trans alkene+NaRCCRHRCCRH+Na+An alkenyl anionAn alkenyl anion.:R RC CC CR RH H+R RC CC CR RH HH HA A t tr ra an ns s a al lk ke en ne eH HN NH HH HH HN NH HA A m m i id de e i io on nOrganic SynthesisuA successful s
43、ynthesis must provide the desired product in maximum yield have the maximum control of stereochemistry and regiochemistry do minimum damage to the environment(it must be a“green”synthesis)uOur strategy will be to work backwards from the target moleculeOrganic SynthesisuWe analyze a target molecule i
44、n the following ways the carbon skeleton:how can we put it together.Our only method to date for forming new a C-C bond is the alkylation of alkyne anions(Section 7.5)the functional groups:what are they,how can they be used in forming the carbon-skeleton of the target molecule,and how can they be cha
45、nged to give the functional groups of the target moleculeOrganic SynthesisuWe use a method called a retrosynthesis and use an open arrow to symbolize a step in a retrosynthesis a process of reasoning backwards from a target molecule to a set of suitable starting materialstargettargetmoleculemolecule
46、startingstartingmaterialsmaterialsOrganic SynthesisuTarget molecule:cis-3-hexene-:C CC C:-2 2 C C H H3 3C C H H2 2B B r rc ci is s-3 3-H H e ex xe en ne e+3 3-H H e ex xy yn ne eA A c ce et ty yl li id de e d di ia an ni io on nB Br ro om m o oe et th ha an ne ed di i s sc co on nn ne ec ct t h he e
47、r re eOrganic Synthesis starting materials are acetylene and bromoethanec ci is s-3 3-H H e ex xe en ne e3 3-H H e ex xy yn ne eH H C CC CH H1 1.N N a aN N H H2 23 3.N Na aN N H H2 22 2.C CH H3 3C CH H2 2B Br r4 4.C CH H3 3C CH H2 2B Br r5 5.H H2 2L Li in nd dl la ar rc ca at ta al ly ys st tA A c c
48、e et ty yl le en ne e1 1-B Bu ut ty yn ne eOrganic SynthesisuTarget molecule:2-heptanone2 2-H H e ep pt ta an no on ne e1 1-H H e ep pt ty yn ne e2 2-H H e ep pt ty yn ne eH HC CC C-+A A c ce et ty yl li id de e a an ni io on n1 1-B Br ro om m o op pe en nt ta an ne eA A n n a ac ci id d-c ca at ta
49、al ly yz ze ed d h hy yd dr ra at ti io on no of f t th hi is s a al lk ky yn ne e g gi iv ve es s a a m m i ix xt tu ur re e o of f 2 2-h he ep pt ta an no on ne e a an nd d 3 3-h he ep pt ta an no on ne eO OB Br rA A n n a ac ci id d-c ca at ta al ly yz ze ed d h hy yd dr ra at ti io on n o of f t
50、 th hi is sa al lk ky yn ne e g gi iv ve es s 2 2-h he ep pt ta an no on ne eOrganic Synthesis starting materials are acetylene and 1-bromopentane2 2-H H e ep pt ta an no on ne e1 1-H H e ep pt t y yn ne eO OB Br rH H C CC CH H1 1.N N a aN N H H2 22 2.3 3.H H2 2O OH H2 2S SO O4 4,H Hg gS SO O4 4Alky
