Conceptually new chiral tertiary C2 symmetric diamines in asymmetric synthesis

Lithiation–Electrophilic Substitution of N‐Thiopivaloylazetidine

“…Proline-based ligands 7 and 8 were less effective than sparteine ( Table 2, entries 8-11). [19] Alexakis and co-workers originally introduced trans-cyclohexane-1,2diamines, such as 9 (now commercially available), [20] as ligands for the enantioselective addition of methyllithium to imines, in which the different substituents on each nitrogen atom allowed both heteroatoms to become stereocenters when chelated to the metal; [21] more recently, this diamine has been shown to induce asymmetric a lithiation of N-Bocpyrrolidine with high efficiency, comparable to that obtained with (À)-sparteine (6). [22] When thioamide 4 was used as the substrate, although ligand 9 (in hexane) gave a lower e.r.…”

Lithiation–Electrophilic Substitution of N‐Thiopivaloylazetidine

“…Proline‐based ligands 7 and 8 were less effective than sparteine (Table 2, entries 8–11) 19. Alexakis and co‐workers originally introduced trans ‐cyclohexane‐1,2‐diamines, such as 9 (now commercially available),20 as ligands for the enantioselective addition of methyllithium to imines, in which the different substituents on each nitrogen atom allowed both heteroatoms to become stereocenters when chelated to the metal;21 more recently, this diamine has been shown to induce asymmetric α lithiation of N ‐Boc‐pyrrolidine with high efficiency, comparable to that obtained with (−)‐sparteine ( 6 ) 22. When thioamide 4 was used as the substrate, although ligand 9 (in hexane) gave a lower e.r.…”

The Use of (−)‐Sparteine/Organolithium Reagents for the Enantioselective Lithiation of 7,8‐Dipropyltetrathia[7]helicene: Single and Double Kinetic Resolution Procedures

“…[52] Similarly (M)-3,w hich with sBuLi is always formed in excellent ee,w as isolated in only 23 % ee from comparabler eactions that employed the sparteine surrogate. Another well developed chiral diamine system, the Alexakis TMCDAd erivative [28] (Figure 3b), was also briefly examined. Using the Alexakis diamine and sBuLi (5:1 ratio), (P)-2 waso btained in 46 % conversion and 2% ee and (M)-3 in 11 %c onversion and 28 % ee.I ti sn otable that with all three diamines examined so far, the level of ee of the disilyl product from double lithiation is significantly highert hat the ee of the corresponding monosilyl product.…”