Allylic/benzylic amines, approaches

The Cr-PILC catalyzed benzylic and allylic oxidations also provide a facile approach to the oxidative deprotection of allyl and benzyl ethers and amines. Treatment of allyl or benzyl ethers with one equivalent of tert-butyl hydroperoxide in the presence of Cr-PILC at room temperature resulted in the oxidative cleavage of the allyl- or benzyl-oxygen bond to give the alcohol but when two equivalents of tert-butyl hydroperoxide (TBHP) were used, the alcohol was oxidized further to the aldehyde or ketone (Eqn. 21.21).47 Oxidation of allyl amines resulted in the cleavage of the allyl-nitrogen bond to give the des-allyl amine.47 Benzyl amines, however, were oxidized to the benzamides (Eqn. 21.22).45... 

Figure 1.9 Various approaches to allylic and benzylic amines.

Chiral addition of allyl metals to imines is one of the useful approaches toward the synthesis of homoallylic amines. These amines can be readily converted to a variety of biologically important molecules such as a-, / -, and y-amino acids. Itsuno and co-workers utilized the allylborane 174 derived from diisopropyl tartrate and cr-pinene for the enantioselective allylboration of imines. The corresponding iV-aluminoimines 173 are readily available from the nitriles via partial reduction using diisobutylaluminium hydride (DIBAL-H) <1999JOM103>. Recently, iV-benzyl-imines 176 have also been utilized for the asymmetric allylboration with allylpinacol boronate 177 in the presence of chiral phosphines as the chiral auxiliaries to obtain homoallylic A -benzylamines 178 in high yield and selectivity (Scheme 29) <2006JA7687>. 

The most efficient method for the stereoselective formation of amines through rhodium(II)-catalyzed intermolecular C(sp )-H amination, to date, involves a diastereoselective approach based on the synergistic interaction between the stdfonimidamide (S)-7 and the chiral rhodium complex Rh2(S-nta)4 8. Benzylic and allylic amines are isolated from various complex substrates used as the limiting component, in excellent yields of up to 99% and complete stereocontrol (Scheme 34). Of course, the other enantiomer is also efficiendy accessible through the use of the other matched pair of reagents. 

Chagnault and coworkers reported a convenient one-step approach to iV-glucosylamines enabling the installation of (benzyl, nonyl and allyl)amine moieties at C-1. The synthetic approach starts from benzyl protected lactol as depicted in Scheme 6. 

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