1559T_ch18_323-34311/3/0511:12Page328 EQA 328.Chapter 18 ENOLS,ENOLATES,AND THE ALDOL CONDENSATION:B-UNSATURATED ALDEHYDES AND KETONES 32 33.a (b)3-Pentanone H2C=CHCH3 (d)3-Pentanone +H2C-C(CHa) CH.CH(CHz akylation sequences.The new carbon carbon bond is marked with (a)(CHaC-CHCHCHCHO ac=H-○ u te and iodomethan
32. 35. Illustrated with cyclohexanone: Before the reaction between cyclohexanone enolate and iodomethane has gone to completion, a mixture is present containing CH3 O CH3I, , and O SO2 Cl O O Cl O H O H H H O H O S O Cl Cl H Cl H H H H 328 • Chapter 18 ENOLS, ENOLATES, AND THE ALDOL CONDENSATION: , -UNSATURATED ALDEHYDES AND KETONES 33. (a) (b) 3-Pentanone H2CPCHCH3 (c) (d) 3-Pentanone H2CPC(CH3)2 (b) and (d) show the results of E2 elimination: Alkylation requires an SN2 process and you already know that these are poor with secondary and impossible with tertiary haloalkanes. CH2CH(CH3)2 O CH2CH3 O 34. Both are aldehyde n enamine n alkylation sequences. The new carbon–carbon bond is marked with an arrow. (a) (b) CH2 CHCHO (via CH2 Br CH CH N SN2 reaction) (CH3)2C CHCH2 CH2CHO via CH2 CH N 1559T_ch18_323-343 11/3/05 11:12 Page 328
1559r_eh18_323-34311/3/0511:12Page329 EQA one can take place unde &8m-8m 36.Yes.Enamines (neutral)are much less basic than enolates (anionic)and show much less tendency to cause E2 elimination reactions. 37.Use the catalyst!Then it's straightforward 号号牙子 风 -心9 (E and Z E and
An acid-base reaction between cyclohexanone enolate and 2-methylcyclohexanone can take place under these conditions, leading to either possible enolate of the latter. Reaction of the new enolates with CH3I leads to double alkylation products. Enamines reduce this problem. They are less reactive and more selective than enolate ions. 36. Yes. Enamines (neutral) are much less basic than enolates (anionic) and show much less tendency to cause E2 elimination reactions. 37. Use the catalyst! Then it’s straightforward: 38. The direction of nucleophilic attack is shown, and the new bond is marked in the product with an arrow. Both the initial hydroxycarbonyl compound and the enone that forms upon dehydration are shown. (a) (b) OH CHO CHO and (E and Z) O H O H OH CHO CHO and (E and Z) O H O H N H H H N OH N H O H (Section 17-8) O N N N O N H H2O H H O O O H H H O H H CH3 CH3 O CH3 or Solutions to Problems • 329 1559T_ch18_323-343 11/3/05 11:12 Page 329