Page 268 - Advanced Organic Chemistry Part A - Structure and Mechanisms, 5th ed (2007) - Carey _ Sundberg
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248                            Table 2.22P. Energy Difference between syn and anti
                                                    Conformations
     CHAPTER 2
                                     Substituent           E syn −E anti (kcal/mol)
     Stereochemistry,
     Conformation,                                     Vacuum            = 4	7
     and Stereoselectivity
                                        H              +0	60           +0	65
                                        F              −0	34           +0	74
                                        Cl             −0	97           −0	02
                                        Br             −1	36           −0	57
                                       CN              −1	07           −0	21
                                                       +0	46           +1	85
                                       NO 2

                                    b.

                                                                            OH
                                               O
                                                           LiB(Et) H
                                                                3
                                         Ph           OCH 3           Ph          OCH 3
                                                                              SPh
                                                  SPh
                                                                        92:8 favoring syn
                       2.24. Either oxaborazolidine-catalysis (Me-CBS) or  Ipc  BCl reductions can be used
                                                                      2
                            to prepare 24-A a precursor of Fluoxetine (Prozac)® in good yield and high e.e.
                            Suggest transition structures that account for the observed enantioselectivity.

                                                   Ph       O        NH 3
                                        Ipc 2 BCl       O
                           O                                        CH 3 OH   OH
                                                     97–99% e.e.
                         PhCCH 2 CH 2 CO 2 CH 3
                                                                           Ph   CH 2 CH 2 CONH 2
                                                    OH
                                        BH 3
                                        Me-CBS                          NH 3        24-A
                                                  Ph
                                                      CH 2 CH 2 CO 2 CH 3
                                                                      CH 3 OH
                                        CF 3
                                                    96% e.e.
                                O
                                     NHCH 3
                               R-Fluoxetine

                        2.25 Some of the compounds shown below contain enantiotopic or diastereotopic
                            atoms or groups. Which possess this characteristic? For those that do, indicate
                            the atoms or groups that are diastereotopic and assign the groups as pro-R and
                            pro-S.
                                                         O
                                  CH 3  CH 3
                             a.                  b.                       c.         CH(CH )
                                                         S                    PhCHCO 2    3 2
                                      O              CH 3  CH 3                OCH 3
                                                            O
                             d.                  e.                       f.
                                (CH ) CHCHCO 2 –     PhCH CHCNHCH CO H       BrCH 2 CH(OC 2 H 5 ) 2
                                                         2
                                   3 2
                                                                     2
                                                                  2
                                       NH 3 +             NH 2
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