csee CHAPTER 14 ○ RGANOMETALLIC COMP○UNDS SOLUTIONS TO TEXT PROBLEMS 14.1 (b) Magnesium bears a cyclohexyl substituent and a chlorine. Chlorine is named as an anion. The ompound is cyclohexylmagnesium chloride 14.2(b) The alkyl bromide precursor to sec-butyllithium must be sec-butyl bromide. CH3 CHCH, CH3 2Li CH,CHCH, CH3 LiBr 2-Bromobutane (sec-butyl bromide) 14.3(b) Allyl chloride is converted to allylmagnesium chloride on reaction with magnesium. H,C=CHCH,CI H,C-CHCH,MgCI Allyl chloride lylmagnesium chloride (c) The carbon-iodine bond of iodocyclobutane is replaced by a carbon-magnesium bond in the gnard reagent. lodocyclobutane 342 Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
CHAPTER 14 ORGANOMETALLIC COMPOUNDS SOLUTIONS TO TEXT PROBLEMS 14.1 (b) Magnesium bears a cyclohexyl substituent and a chlorine. Chlorine is named as an anion. The compound is cyclohexylmagnesium chloride. 14.2 (b) The alkyl bromide precursor to sec-butyllithium must be sec-butyl bromide. 14.3 (b) Allyl chloride is converted to allylmagnesium chloride on reaction with magnesium. (c) The carbon–iodine bond of iodocyclobutane is replaced by a carbon–magnesium bond in the Grignard reagent. Mg diethyl ether Iodocyclobutane I Cyclobutylmagnesium iodide MgI Allyl chloride H CHCH2Cl 2C Allylmagnesium chloride H CHCH2MgCl 2C Mg diethyl ether CH 2Li LiBr 3CHCH2CH3 Br 2-Bromobutane (sec-butyl bromide) CH3CHCH2CH3 Li 1-Methylpropyllithium (sec-butyllithium) 342 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
ORGANOMETALLIC COMPOUNDS 343 (d) Bromine is attached to an sp-hybridized carbon in 1-bromocyclohexene. The product of its reaction with magnesium has a carbon-magnesium bond in place of the carbon-bromine MgBr diethyl ether I-Bromocyclohexene 14.4(b) 1-Hexanol will protonate butyllithium because its hydroxyl group is a proton donor only slightly less acidic than water. This proton-transfer reaction could be used to prepare lithium I-hexanolate CHa CH, CH,CH,CH,CH,OH CHCH,CH,CH,Li CH3 CH,, CH3 CHCH,CH, CH,CH, CH,OLi 1-Hexanol Butyllithium Butane Lithium 1-hexanolate (c) The proton donor here is benzenethiol. C6HSSH CH,CHCH,CH,Li CH, CHCHCH ChSLi Benzenethiol Butyllithium Butane Lithium 14.5(b) Propylmagnesium bromide reacts with benzaldehyde by addition to the carbonyl group CHI CH2CH2T-MgBr CHCHCH diethyl ether C6H CTO C6HSC-OMg Br C6HSCHCH,CH,CH 1-Phenyl-1-but (c) Tertiary alcohols result from the reaction of Grignard reagents and ketones CHCHCI CHa CH,CH,Mg Br 1-Propylcyclohexanol (d) The starting material is a ketone and so reacts with a Grignard reagent to give a tertiary alcohol H,CH,CH2-MgE H C CH, CHCH diethyl ether CHaCH,CH,CO CHa CH, Propylmagnesium bromide 3-Methyl-3-hexanol Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
(d) Bromine is attached to an sp2 -hybridized carbon in 1-bromocyclohexene. The product of its reaction with magnesium has a carbon–magnesium bond in place of the carbon–bromine bond. 14.4 (b) 1-Hexanol will protonate butyllithium because its hydroxyl group is a proton donor only slightly less acidic than water. This proton-transfer reaction could be used to prepare lithium 1-hexanolate. (c) The proton donor here is benzenethiol. 14.5 (b) Propylmagnesium bromide reacts with benzaldehyde by addition to the carbonyl group. (c) Tertiary alcohols result from the reaction of Grignard reagents and ketones. (d) The starting material is a ketone and so reacts with a Grignard reagent to give a tertiary alcohol. diethyl ether H3O CH3CH2CH2 H3C C OMgBr CH3CH2 3-Methyl-3-hexanol CH3CH2CH2COH CH2CH3 CH3 CH3CH2CH2 MgBr O CH3CH2 C H3C Propylmagnesium bromide 2-butanone 1. diethyl ether 2. H3O CH3CH2CH2MgBr O CH2CH2CH3 OH 1-Propylcyclohexanol diethyl ether H3O C6H5C O H CH3CH2CH2 C6H5C OMgBr H 1-Phenyl-1-butanol C6H5CHCH2CH2CH3 OH CH3CH2CH2 MgBr C6H5SH Benzenethiol C6H5SLi Lithium benzenethiolate CH3CH2CH2CH2Li Butyllithium CH3CH2CH2CH3 Butane CH3CH2CH2CH2CH2CH2OH 1-Hexanol CH3CH2CH2CH2CH2CH2OLi Lithium 1-hexanolate CH3CH2CH2CH2Li Butyllithium CH3CH2CH2CH3 Butane Mg diethyl ether 1-Bromocyclohexene Br 1-Cyclohexenylmagnesium bromide MgBr ORGANOMETALLIC COMPOUNDS 343 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
344 ORGANOMETALLIC COMPOUNDS removed because it is the most acidic, having a pK of approximately 2s Vne. The proton at C-1 is 14.6 Ethyl anion reacts as a Bronsted base to remove a proton from the alky CH2CH2+H-C≡CCH2CH2CH2CH3—CH2CH3+:C≡ CCHCH2CH2CH I-Hexyne Ethane Conjugate base of 1-hexyne 14.7(b) The target alcohol is tertiary and so is prepared by addition of a grignard reagent to a ketone. The retrosynthetic transformations are: CH3-C--CH3 CH CHiCH Because two of the alkyl groups on the hydroxyl-bearing carbon are the same(methyl), only two, not three, different ketones are possible starting materials O CH,Mgl+ CCH 1. diethyl ether CCH 2.H3O CH Methylmagnesium diethyl ether MgBr CH,CCH -CCH Acetone 2-Phenyl-2-propand 14.8(b) Recall that the two identical groups bonded to the hydroxyl-bearing carbon of the alcohol arose from the Grignard reagent. That leads to the following retrosynthetic analysis (C6H5)2 COR t 2CHs MgX Thus, the two phenyl substituents arise by addition of a phenyl grignard reagent to an ester of cyclopropanecarboxylic acid. L diethyl ether 2CH-MgBr COCH 2. H,o+(CH3)2C ChOH Phenylmagnesium carboxylate diphenylmethanol 14.9(b) Of the three methyl groups of 1, 3, 3-trimethylcyclopentene, only the one connected to the double bond can be attached by way of an organocuprate reagent Attachment of either of Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
344 ORGANOMETALLIC COMPOUNDS 14.6 Ethyl anion reacts as a Brønsted base to remove a proton from the alkyne. The proton at C-1 is removed because it is the most acidic, having a pKa of approximately 25. 14.7 (b) The target alcohol is tertiary and so is prepared by addition of a Grignard reagent to a ketone. The retrosynthetic transformations are: Because two of the alkyl groups on the hydroxyl-bearing carbon are the same (methyl), only two, not three,different ketones are possible starting materials: 14.8 (b) Recall that the two identical groups bonded to the hydroxyl-bearing carbon of the alcohol arose from the Grignard reagent. That leads to the following retrosynthetic analysis: Thus, the two phenyl substituents arise by addition of a phenyl Grignard reagent to an ester of cyclopropanecarboxylic acid. 14.9 (b) Of the three methyl groups of 1,3,3-trimethylcyclopentene, only the one connected to the double bond can be attached by way of an organocuprate reagent. Attachment of either of 1. diethyl ether 2. H3O (C6H5)2C OH Cyclopropyldiphenylmethanol CH3OH Methanol O COCH3 Methyl cyclopropanecarboxylate 2C6H5MgBr Phenylmagnesium bromide (C6H5)2C OH O COR 2C 6H5MgX MgBr CH3CCH3 O Phenylmagnesium bromide Acetone CCH3 1. diethyl ether 2. H3O OH CH3 2-Phenyl-2-propanol CH3MgI CCH3 CCH3 1. diethyl ether 2. H3O O OH CH3 Methylmagnesium iodide Acetophenone 2-Phenyl-2-propanol CH3 C O CH3 C OH CH3 CH3 CH3CCH3 O CH3CH3 1-Hexyne Ethane H C CCH2CH2CH2CH3 Ethyl anion CH3CH2 Conjugate base of 1-hexyne C CCH2CH2CH2CH3 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
ORGANOMETALLIC COMPOUNDS 345 the other methyls would involve a tertiary carbon, a process that does not occur very efficiently. CH iCu(CHs),+ Br H3 Lithiun 1.3, 3-Trimethylcyclopentene dimethylcyclope 14.10(b) Methylenecyclobutane is the appropriate precursor to the spirohexane shown CH,I Spiro[3.2 ]hexane(22%0) 14.11 Syn addition of dibromocarbene to cis-2-butene yields a cyclopropane derivative in which the methyl groups are cis C CHBr H, CI KoC(CHi) cis-2-Butene cis-l, l-Dibromo-2.3. Conversely, the methyl groups in the cyclopropane derivative of trans-2-butene are trans to one H3C CH trans-2-Butene trans-1, I-Dibromo-2.3. dimethylcyclopropane 14.12 Iron has an atomic number of 26 and an electron configuration of [Arl45-3do. Thus, it has 8 valence electrons and requires 10 more to satisfy the 18-electron rule. Five CO ligands, each providing two electrons, are therefore needed. The compound is Fe(co) 14.13 (a) Cyclopentyllithium is It has a carbon-lithium bond. It satisfies the requirement for classification as an organo- (b) Ethoxymagnesium chloride does not have a carbon-metal bond. It is not an organometallic CH, CHOMgC CH,CH,O Mg Cl (c) 2-Phenylethylmagnesium iodide is an example of a Grignard reagent. It is an organometallic Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
the other methyls would involve a tertiary carbon, a process that does not occur very efficiently. 14.10 (b) Methylenecyclobutane is the appropriate precursor to the spirohexane shown. 14.11 Syn addition of dibromocarbene to cis-2-butene yields a cyclopropane derivative in which the methyl groups are cis. Conversely, the methyl groups in the cyclopropane derivative of trans-2-butene are trans to one another. 14.12 Iron has an atomic number of 26 and an electron configuration of [Ar]4s 2 3d6 . Thus, it has 8 valence electrons and requires 10 more to satisfy the 18-electron rule. Five CO ligands, each providing two electrons, are therefore needed. The compound is Fe(CO)5. 14.13 (a) Cyclopentyllithium is It has a carbon–lithium bond. It satisfies the requirement for classification as an organometallic compound. (b) Ethoxymagnesium chloride does not have a carbon–metal bond. It is not an organometallic compound. (c) 2-Phenylethylmagnesium iodide is an example of a Grignard reagent. It is an organometallic compound. CH2CH2MgI CH3CH2OMgCl CH3CH2O Mg2 Cl or H Li C C H H3C CH3 H trans-2-Butene trans-1,1-Dibromo-2,3- dimethylcyclopropane CHBr3 KOC(CH3)3 H3C CH3 Br Br H H C C H H3C CH3 H cis-2-Butene cis-1,1-Dibromo-2,3- dimethylcyclopropane H3C CH3 Br Br H H CHBr3 KOC(CH3)3 CH2I2 Zn(Cu), ether CH2 Methylenecyclobutane Spiro[3.2]hexane (22%) LiCu(CH3)2 diethyl ether 1-Bromo-3,3- 1,3,3-Trimethylcyclopentene dimethylcyclopentene Lithium dimethylcuprate CH3 CH3 Br H3C CH3 CH3 ORGANOMETALLIC COMPOUNDS 345 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
346 (d) Lithium divinylcuprate has two vinyl groups bonded to copper. It is an organometallic Li(H,C=CH-Cu-CH=CH, (e) Sodium carbonate, Na,CO3 can be represented by the Lewis structure There is no carbon-metal bond, and sodium carbonate is not an org ff Benzylpotassium is represented as CHK or CH K It has a carbon-potassium bond and thus is an organometallic compound. 14.14 The two alkyl groups attached to aluminum in [(CH3),,JAlH are isobutyl groups. The hy drogen bonded to aluminum is named in a separate word as hydride. Thus, dibal"is a shortened form of the systematic name diisobutylaluminum hydride. 14.15 (a) Grignard reagents such as pentylmagnesium iodide are prepared by reaction of magnesium with the corresponding alkyl halide diethyl ethe CH CH, CH, CH,CH,I Mg CHa CH,CH,CH, CH,Mgl b) Acetylenic Grignard reagents are normally prepared by reaction of a terminal alkyne with a readily available Grignard reagent such as an ethylmagnesium halide. The reaction that takes place is an acid-base reaction in which the terminal alkyne acts as a proton donor diethyl ether CH2CHC≡CH+CHCH2MgI CH3CHC≡CMgI+CH3CH3 1-Butyne Ethylmagnesium 1-Butynylmagnesium Ethane (c) Alkyllithiums are formed by reaction of lithium with an alkyl halide. CHCH,CH,CH,CH,X 2Li CH, CH, CH,CH, Li Lix (X= Cl Br, or D (d) Lithium dialkylcuprates arise by the reaction of an alkyllithium with a Cu(r) salt. 2CH CHCH.CHCHL LiCu(CH, CH, CH,CHa CH3)2+ Lix Pentyllithium, from part(c) (X=Cl, Br. or D) Lithium dipentylcuprate 14.16 The polarity of a covalent bond increases with an increase in the electronegativity difference be- tween the connected atoms. Carbon has an electronegativity of 2.5 (Table 14. 1). Metals are less elec- tronegative than carbon. When comparing two metals, the less electronegative one therefore has the Po (a) Table 14.1 gives the electronegativity of lithium as 1.0, whereas that for aluminum is 1.5. The carbon-lithium bond in CH,CH,Li is more polar than the carbon-aluminum bond in (CH,,)3AL. Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
(d) Lithium divinylcuprate has two vinyl groups bonded to copper. It is an organometallic compound. (e) Sodium carbonate, Na2CO3 can be represented by the Lewis structure. There is no carbon–metal bond, and sodium carbonate is not an organometallic compound. (f) Benzylpotassium is represented as It has a carbon–potassium bond and thus is an organometallic compound. 14.14 The two alkyl groups attached to aluminum in [(CH3)2CHCH2]2AlH are isobutyl groups. The hydrogen bonded to aluminum is named in a separate word as hydride. Thus, “dibal” is a shortened form of the systematic name diisobutylaluminum hydride. 14.15 (a) Grignard reagents such as pentylmagnesium iodide are prepared by reaction of magnesium with the corresponding alkyl halide. (b) Acetylenic Grignard reagents are normally prepared by reaction of a terminal alkyne with a readily available Grignard reagent such as an ethylmagnesium halide. The reaction that takes place is an acid–base reaction in which the terminal alkyne acts as a proton donor. (c) Alkyllithiums are formed by reaction of lithium with an alkyl halide. (d) Lithium dialkylcuprates arise by the reaction of an alkyllithium with a Cu(I) salt. 14.16 The polarity of a covalent bond increases with an increase in the electronegativity difference between the connected atoms. Carbon has an electronegativity of 2.5 (Table 14.1). Metals are less electronegative than carbon. When comparing two metals, the less electronegative one therefore has the more polar bond to carbon. (a) Table 14.1 gives the electronegativity of lithium as 1.0, whereas that for aluminum is 1.5. The carbon–lithium bond in CH3CH2Li is more polar than the carbon–aluminum bond in (CH3CH2)3Al. CuX Pentyllithium, from part (c) (X Cl, Br, or I) 2CH3CH2CH2CH2CH2Li LiX Lithium dipentylcuprate LiCu(CH2CH2CH2CH2CH3)2 2Li 1-Halopentane (X Cl, Br, or I) CH3CH2CH2CH2CH2X LiX Pentyllithium CH3CH2CH2CH2CH2Li diethyl ether CH3CH2MgI Ethylmagnesium iodide CH3CH3 1-Butyne Ethane CH3CH2C CH 1-Butynylmagnesium iodide CH3CH2C CMgI Mg diethyl ether CH3CH2CH2CH2CH2I 1-Iodopentane CH3CH2CH2CH2CH2MgI Pentylmagnesium iodide CH or 2K CH2 K Na O C O O Na Li(H2C CH CH2 Cu CH ) 346 ORGANOMETALLIC COMPOUNDS Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
ORGANOMETALLIC COMPOUNDS 347 (b) The electronegativity of magnesium(1. 2)is less than that of zinc(1.6).( CH3)2,Mg therefore has a more polar carbon-metal bond than( CH3),Zn (c) In this part of the problem two Grignard reagents are compared. Magnesium is the metal in both cases. The difference is the hybridization state of carbon. The sp-hybridized carbon in HCECMgBr is more electronegative than the sp-hybridized carbon in CHCH, Mg Br, and HCECMgBr has a more polar carbon-magnesium bond. 14.17(a) CH, CH, CH, Br 2Li diethyl ether CH CH CHLi LiBr Propyllithium (b) CH, CH, CH, Br Mg diethyl ether CH,CH,CH, MgBr 1-Bromopropane (c) CH CHCH 2Li diethyl ether, CH,CHCH, +Lil propyllithiu (d) CH, CHCH,+Mg CH CHCH Mgl 2-lodopropane (e) 2CH, CHCH,Li Cul (CH CH2CH2)cUlI Propyllithium Lithium dipropylcuprate (f)(CH, CH,CH,), CuLi CH_ CH, CH, CH, Br CHaCH,CHCH,CH,CH,CH Lithium dipropylcuprat 1-Bromobutane CH, CH,CH3 8)(CH,CH,CH,),CuLi+ Lithium dipropylcuprate iodobenzene Propylbenzene h) CH,CH, CH,Mg BI D CH3 D Propylmagnesium I-Deuteriopropane (i) CH,CHCH CH, CHCH 2-Deuteriopro ( CH,CH,CH, Li + HCH diethyl ether CH CHCHCH OH ropyllithium 1-Butanol Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
(b) The electronegativity of magnesium (1.2) is less than that of zinc (1.6). (CH3)2Mg therefore has a more polar carbon–metal bond than (CH3)2Zn. (c) In this part of the problem two Grignard reagents are compared. Magnesium is the metal in both cases. The difference is the hybridization state of carbon. The sp-hybridized carbon in HC>CMgBr is more electronegative than the sp3 -hybridized carbon in CH3CH2MgBr, and HC>CMgBr has a more polar carbon–magnesium bond. 14.17 (a) (b) (c) (d) (e) ( f ) (g) (h) (i) ( j) 1. diethyl ether 2. H3O Propyllithium CH3CH2CH2Li 1-Butanol HCH CH3CH2CH2CH2OH O D2O DCl Isopropyllithium CH3CHCH3 Li 2-Deuteriopropane CH3CHCH3 D Propylmagnesium bromide CH3CH2CH2MgBr 1-Deuteriopropane CH3CH2CH2D D2O DCl Lithium dipropylcuprate Iodobenzene Propylbenzene (CH3CH2CH2)2CuLi I CH2CH2CH3 Heptane CH3CH2CH2CH2Br CH3CH2CH2CH2CH2CH2CH3 Lithium dipropylcuprate 1-Bromobutane (CH3CH2CH2)2CuLi CuI Propyllithium 2CH3CH2CH2Li Lithium dipropylcuprate (CH3CH2CH2)2CuLi diethyl ether Mg 2-Iodopropane Isopropylmagnesium iodide MgI CH3CHCH3 CH3CHCH3 I diethyl ether 2Li 2-Iodopropane CH3CHCH3 LiI Isopropyllithium Li CH3CHCH3 I diethyl ether Mg 1-Bromopropane CH3CH2CH2Br Propylmagnesium bromide CH3CH2CH2MgBr diethyl ether 2Li 1-Bromopropane CH3CH2CH2Br LiBr Propyllithium CH3CH2CH2Li ORGANOMETALLIC COMPOUNDS 347 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
348 ORGANOMETALLIC COMPOUNDS () CH_ CH_CH2MgBr CH 1.diethyl ether CHCHCHCH 2.H.0 opylmagnesium 1-Phenyl-1-butanol 1. diethyl ethe () CH; CHCH3+ (CH3),CH OH Isopropyllithium cycloheptanone (m) CH, CHCH, CH CCHChs 2,go CHCH-CCHCH Mgl CH3 CH3 isopropyl magnesium iodide (n) 2CH,CH, CH,MgBr CBH_ COCH I diethyl et C6H5C(CH, CH, CH3)2 CH,OH Propylmagnesit Methyl benzoate 4-Phenyl-4-heptanol bromide CHAL (o) H2C=CH(CH2)5CH3 Znic Zn(Cu), diethyl ether H,C-CH(CH,)SCH3 1-Octene H,C CH, L, Zn(Cu), diethyl (CH,) CH H(CH,)CH3 (Er-2-Decene trans-1-Heptyl-2 CH,CH (CH2) CH H,1 CHCH2i CH,I-CE Zn(Cu), diethyl ether HH (Z)-3-Decene (r) HC=CHCH CH,CH, KOc(CH : H"kaC CHCh CH 1-Pentene 1. 1-Dibromo-2-propylcyclopropane 14.18 In the solutions to this problem, the Grignard reagent butylmagnesium bromide is used In each case the use of butyllithium would be equally satisfactory Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
(k) (l) (m) (n) (o) (p) (q) (r) 14.18 In the solutions to this problem, the Grignard reagent butylmagnesium bromide is used. In each case the use of butyllithium would be equally satisfactory. 1-Pentene H2C CHCH2CH2CH3 CHBr3 KOC(CH3)3 1,1-Dibromo-2-propylcyclopropane H CH2CH2CH3 H H Br Br cis-1-Ethyl-2-hexylcyclopropane CH2I2 Zn(Cu), diethyl ether C C H CH3CH2 H (CH2)5CH3 (Z)-3-Decene CH3CH2 (CH2)5CH3 H H trans-1-Heptyl-2- methylcyclopropane CH2I2 Zn(Cu), diethyl ether C C H H3C (CH2)6CH3 H (E)-2-Decene H3C H H (CH2)6CH3 CH2I2 1-Octene Zn(Cu), diethyl ether 1-Cyclopropylhexane H2C CH2 CH(CH2) CH(CH2 5CH3 ) H2C 5CH3 2CH3CH2CH2MgBr Propylmagnesium bromide Methyl benzoate C6H5COCH3 O 1. diethyl ether 2. H3O 4-Phenyl-4-heptanol C6H5C(CH2CH2CH3)2 CH3OH OH Methanol 2-Butanone CH3CCH2CH3 O 1. diethyl ether 2. H3O 2,3-Dimethyl-3-pentanol CH3CH CCH2CH3 OH CH3 CH3 Isopropylmagnesium iodide CH3CHCH3 MgI Isopropyllithium CH3CHCH3 Li 1. diethyl ether 2. H3O Cycloheptanone O 1-Isopropylcycloheptanol (CH3)2CH OH Propylmagnesium bromide CH3CH2CH2MgBr Benzaldehyde CH O 1-Phenyl-1-butanol CHCH2CH2CH3 OH 1. diethyl ether 2. H3O 348 ORGANOMETALLIC COMPOUNDS Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
ORGANOMETALLIC COMPOUNDS 349 (a) 1-Pentanol is a primary alcohol having one more carbon atom than 1-bromobutane. Retrosyn- thetic analysis suggests the reaction of a Grignard reagent with formaldehyde CH,CHCH,CH,+CH,OH CH CH, CH,CH Mgx HC=( 1-Pentanol Butylmagnesium halid Formaldehyde An appropriate synthetic scheme is CH3 CH,CH,CH, Br CHa CH,CH,CH,MgBr CH3 CH, CH,CH,CH,OH 1-Pentanol (b) 2-Hexanol is a secondary alcohol having two more carbon atoms than l-bromobutane vealed by retrosynthetic analysis, it may be prepared by reaction of ethanal(acetaldeh ith butylmagnesium bromide CHCHCH,,+CHCH,> CHCH,,Mgx + CHCH OH 2-Hexanol Buty magnesium halide acetaldehyde The correct reaction sequence is I CH,CH CHaCH,CH, BI CHa,CH, CH, MgBr H CHCH..CHCH diethyl ether Butylmagnesium bromide 2-Hexanol (c) 1-Phenyl-l-pentanol is a secondary alcohol Disconnection suggests that it can be prepared from butylmagnesium bromide and an aldehyde; benzaldehyde is the appropriate aldehyde CH,CH, CH, CH,+CH CHaCH,CHCH,Mgx+ I-Phenyl-l-pentanol Butylmagnesium halide Benzaldehyde CHa,CHLCH, Mg Br Fo CHCHCHCHCH Butylmagnesium bromide (d) The target molecule 3-methyl-3-heptanol has the structure CH CH CHCHCH CH, CH3 Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
(a) 1-Pentanol is a primary alcohol having one more carbon atom than 1-bromobutane. Retrosynthetic analysis suggests the reaction of a Grignard reagent with formaldehyde. An appropriate synthetic scheme is (b) 2-Hexanol is a secondary alcohol having two more carbon atoms than 1-bromobutane. As revealed by retrosynthetic analysis, it may be prepared by reaction of ethanal (acetaldehyde) with butylmagnesium bromide. The correct reaction sequence is (c) 1-Phenyl-1-pentanol is a secondary alcohol. Disconnection suggests that it can be prepared from butylmagnesium bromide and an aldehyde; benzaldehyde is the appropriate aldehyde. (d) The target molecule 3-methyl-3-heptanol has the structure C OH CH3 CH3CH2CH2CH2 CH2CH3 1. ether 2. H3O Benzaldehyde CH O 1-Phenyl-1-pentanol CHCH2CH2CH2CH3 OH CH3CH2CH2CH2MgBr Butylmagnesium bromide Butylmagnesium halide CH3CH2CH2CH2MgX 1-Phenyl-1-pentanol CH3CH2CH2CH2 CH OH Benzaldehyde CH O CH3CH2CH2CH2Br 1-Bromobutane Butylmagnesium bromide CH3CH2CH2CH2MgBr 2-Hexanol CH3CH2CH2CH2CHCH3 OH Mg diethyl ether 2. H3O 1. CH3CH O 2-Hexanol Butylmagnesium halide Ethanal (acetaldehyde) CH3CH2CH2CH2MgX CH3CH O CH3CH2CH2CH2 CHCH3 OH CH3CH2CH2CH2Br 1-Bromobutane Mg diethyl ether Butylmagnesium bromide CH3CH2CH2CH2MgBr CH3CH2CH2CH2CH2OH 1-Pentanol 2. H3O 1. HCH O CH3CH2CH2CH2 1-Pentanol Butylmagnesium halide Formaldehyde CH2OH O CH3CH2CH2CH2MgX H2C ORGANOMETALLIC COMPOUNDS 349 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
350 ORGANOMETALLIC COMPOUNDS By retrosynthetically disconnecting the butyl group from the carbon that bears the hydroxy substituent, we see that the appropriate starting ketone is 2-butanone CH3 CH CH, CH CH+C-CH,CH,> CH,CH, CH,Mgx+CCH,CH, Butylmagnesium halide Therefore CHa CH, CH,CH,MgBr CH CCH, CH3 CH3 CH, CH,CH,CCH,CH3 Butylmagnesium bromide 2-Butanone 3.Methyl-3-heptanol (e) 1-Butylcyclobutanol is a tertiary alcohol. The appropriate ketone is cyclobutanone L diethyl ether CHCHCH-CH CHCH,CH,CH, MgBr 2.H.O Buty magnesium bromide Cyclobutanone 1-Butylcyclobutanol 14.19 In each part of this problem in which there is a change in the carbon skeleton, disconnect the phenyl group of the product to reveal the aldehyde or ketone precursor that reacts with the grignard reagent derived from bromobenzene. Recall that reaction of a Grignard reagent with formaldehyde H,C=O)yields a primary alcohol, reaction with an aldehyde(other than formaldehyde) yields a secondary alcohol, and reaction with a ketone yields a tertiary alcohol. (a) Conversion of bromobenzene to benzyl alcohol requires formation of the corresponding Grignard reagent and its reaction with formaldehyde. Retrosynthetically can be seen 3CH.OH MgX hC=O Therefore diethyl Phenylmagnesium Benzyl alcohol (b) The product is a secondary alcohol and is formed by reaction of phenylmagnesium bromide with hexanal FCH(CH,).CH MgX HC(CH))4CH I-Phenyl-l-hexanol Phenylmagnesium Hexanal CHCH,CHCHCH,CH3 CHaCH, CH,CH,CH,CH diethyl ether H,O Hexane Phenyl-l-hexanol Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
By retrosynthetically disconnecting the butyl group from the carbon that bears the hydroxyl substituent, we see that the appropriate starting ketone is 2-butanone. Therefore (e) 1-Butylcyclobutanol is a tertiary alcohol. The appropriate ketone is cyclobutanone. 14.19 In each part of this problem in which there is a change in the carbon skeleton, disconnect the phenyl group of the product to reveal the aldehyde or ketone precursor that reacts with the Grignard reagent derived from bromobenzene. Recall that reaction of a Grignard reagent with formaldehyde (H2C?O) yields a primary alcohol, reaction with an aldehyde (other than formaldehyde) yields a secondary alcohol, and reaction with a ketone yields a tertiary alcohol. (a) Conversion of bromobenzene to benzyl alcohol requires formation of the corresponding Grignard reagent and its reaction with formaldehyde. Retrosynthetically, this can be seen as Therefore, (b) The product is a secondary alcohol and is formed by reaction of phenylmagnesium bromide with hexanal. Hexanal 1-Phenyl-1-hexanol MgBr Phenylmagnesium bromide CH3CH2CH2CH2CH2CH OH CHCH2CH2CH2CH2CH3 O 1. diethyl ether 2. H3O Phenylmagnesium halide Hexanal MgX HC(CH2)4CH3 1-Phenyl-1-hexanol O CH(CH2)4CH3 OH Br Bromobenzene Phenylmagnesium bromide MgBr Benzyl alcohol CH2OH 2. H3O 1. HCH O Mg diethyl ether CH2OH MgX H 2C O Butylmagnesium bromide CH3CH2CH2CH2MgBr 1-Butylcyclobutanol OH 1. diethyl ether CH2CH2CH2CH3 2. H3O Cyclobutanone O CH3CH2CH2CH2MgBr CH CH3CCH2CH3 3CH2CH2CH2CCH2CH3 Butylmagnesium bromide 2-Butanone 3-Methyl-3-heptanol 1. diethyl ether 2. H3O O OH CH3 Butylmagnesium halide CH3CH2CH2CH2 C CH2CH3 CH3CH2CH2CH2MgX OH CH3 2-Butanone CCH2CH3 CH3 O 350 ORGANOMETALLIC COMPOUNDS Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
ORGANOMETALLIC COMPOUNDS 351 (c) The desired product is a secondary alkyl bromide. a reasonable synthesis would be to first prepare the analogous secondary alcohol by reaction of phenylmagnesium bromide with benz- aldehyde, followed by a conversion of the alcohol to the bromide Retrosynthetically this can C6HSCH-C6Hs CHCH.H3□> C6HSMgX+cHCH I diethyl ether HBr or PBrs MgBr t hc- CH一 Phenylmagnesium Benzaldehyde (d) The target molecule is a tertiary alcohol, which requires that phenylmagnesium bromide react with a ketone By mentally disconnecting the phenyl group from the carbon that bears the hydroxyl group, we see that the appropriate ketone is 4-heptanone. CH CH,CH,CCH, CH, CH3 CH,,CH, CCH, CH, CH3 4-Phenyl-4-heptanol 4-Heptanone The synthesis is therefore OH t CHaCH,CH,CCH,CH,CH 1. diethyl ether CHaCH,CH,CCH, CH, CH Phenylmagnesium 4-Heptanone 4-Phenyl-4-heptanol (e) Reaction of phenylmagnesium bromide with cyclooctanone will give the desired tertiary alcohol 1. diethyl ether 2.H3O (f) The 1-phenylcyclooctanol prepared in part (e) of this problem can be subjected to acid- catalyzed dehydration to give l-phenylcyclooctene. Hydroboration-oxidation of 1-phenyl cyclooctene gives trans-2-phenylcyclooctanol H, SO, he 1.B2H6 l-Phenylcyclooctanol I-Phenylcyclooctene trans-2-Phenylcyclooctanol Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
(c) The desired product is a secondary alkyl bromide. A reasonable synthesis would be to first prepare the analogous secondary alcohol by reaction of phenylmagnesium bromide with benzaldehyde, followed by a conversion of the alcohol to the bromide. Retrosynthetically this can be seen as (d) The target molecule is a tertiary alcohol, which requires that phenylmagnesium bromide react with a ketone. By mentally disconnecting the phenyl group from the carbon that bears the hydroxyl group, we see that the appropriate ketone is 4-heptanone. The synthesis is therefore (e) Reaction of phenylmagnesium bromide with cyclooctanone will give the desired tertiary alcohol. ( f) The 1-phenylcyclooctanol prepared in part (e) of this problem can be subjected to acidcatalyzed dehydration to give 1-phenylcyclooctene. Hydroboration–oxidation of 1-phenylcyclooctene gives trans-2-phenylcyclooctanol. H2SO4, heat 1. B2H6 2. H2O2, HO OH 1-Phenylcyclooctanol 1-Phenylcyclooctene H trans-2-Phenylcyclooctanol H H OH O OH 1. diethyl ether 2. H3O Cyclooctanone 1-Phenylcyclooctanol MgBr Phenylmagnesium bromide 1. diethyl ether 2. H3O 4-Heptanone 4-Phenyl-4-heptanol MgBr OH Phenylmagnesium bromide CH3CH2CH2CCH2CH2CH3 CH3CH2CH2CCH2CH2CH3 O 4-Heptanone O CH3CH2CH2CCH2CH2CH3 4-Phenyl-4-heptanol OH CH3CH2CH2CCH2CH2CH3 1. diethyl ether 2. H3O Benzaldehyde Diphenylmethanol CH OH MgBr Bromodiphenylmethane CH Br Phenylmagnesium bromide HC O HBr or PBr3 Br O C6H5CH C6H5 OH C6H5CH C C6H5 6H5MgX C6H5CH ORGANOMETALLIC COMPOUNDS 351 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
