1559r.ch1832334311/3/0511:12Pge333 EQA Solufions to Problems333 45.Retrosynthetically. 盗 Y In addition,both of these processes,as well as the condensation that affords the desired compound give a mixture of E and Zstereoisomers. aldehyde and Cl of the ketone.respectively.By restricting nucleophilic behavior to just the single structure.the t ther.making it the more stable and the likely product of dehydration 红Y45. Retrosynthetically, 46. (a) The desired reaction is a crossed (or mixed) aldol condensation, but one that suffers from competi￾tion with at least two other aldol processes: condensation between two molecules of aldehyde, and condensation of the aldehyde with the methyl group (C1) of the ketone: In addition, both of these processes, as well as the condensation that affords the desired compound, give a mixture of E and Z stereoisomers. (b) This solution forces the formation of just a single nucleophilic enolate carbon, C3 of the ketone. The side reactions described above derive from reaction of nucleophilic enolate ions at C2 of the aldehyde and C1 of the ketone, respectively. By restricting nucleophilic behavior to just the single carbon atom required to allow access to the desired product structure, the two side reactions above are eliminated. In addition, dehydration of the product of this sequence can be controlled to give the necessary stereoisomer, because that isomer places the two larger substituents on the side-chain double bond trans to each other, making it the more stable and the likely product of dehydration under equilibrium (thermodynamic) conditions. Br2, CH3CO2H, CCl4 Mg, ether O O O MgBr Br O HO H O O 1 H KOH, H2O, CH3OH O O O H KOH, H2O, CH3OH H O O O O H  O Solutions to Problems • 333 1559T_ch18_323-343 11/3/05 11:12 Page 333