The ring opening of chiral aziridines is a potent method for the synthesis of optically active amines. [1] The driving force of this process derives from the ring strain of the aziridine and this can be used to extend the ring opening to a variety of nucleophiles to produce difuncational amines with vicinal chiral centers. Since no general method for catalytic asymmetric aziridination exists, [2] chiral aziridines have been largely made from materials in which the chiral centers already exist. [1d] Given the synthetic and strategic advantages of asymmetric catalysis we began a program to find a chiral catalyst for asymmetric aziridination, and recently reported structures of the Group 1 complexes of (S)-[(Ph(Me)-CH)(PhCH 2 )NH] reveal the amido ligand adopts a Βͺbutterfly in flightΒΊ configuration in which the phenyl groups are almost perpendicular to each other, [8] and as such can be viewed as having significant steric bulk with the charge concentrated on the N Γ ion. This is less likely to give stable mixed-anion complexes, and can be contrasted to [{[PhN(H)] 2 (tBuO)Li-NaK Β΄(tmen) 2 } 2 ] and [{(MeOPh)N(H)} 2 (tBuO)NaLi 2 ], both of which are derived from primary amines.
Experimental Section
1: (S)-a-(Ph(Me)CH)(PhCH 2 )NH (5 mmol, 1.05 g) was added dropwise to a chilled (Γ 78 8C) suspension of tBuOK (15mmol, 1.55 g) in hexane (20 mL). nBuLi (5.5 mmol, 3.2 mL, 1.6 m in hexane) was added dropwise resulting in the formation of a bright red suspension. The reaction mixture was stirred and allowed to warm to room temperature over 2 h during which time the suspension darkened to a deeper red. Hexane was removed in vacuo and THF added (ca. 20 mL) which with gentle warming allowed complete dissolution. The ligand tmen (10 mmol, 1.51 mL) was added, then the solvent was reduced in vacuo by approximately a third and the mixture was placed in the freezer at Γ 20 8C overnight. This resulted in a crop of red needlelike crystals which were isolated and then washed with hexane. Yield 57 % (1.7 g). M.p. 131 Β± 132 8C; elemental analysis C 31 H 48 NK 3 O 4 (%); calcd: C 60.5, H 7.8, N 2.3; found: C 61.1, H 7.5, N 2.1; 1 H NMR ([D 8 ]THF, 25 8C, 300 MHz): d 7.21 (d, J 7.9 Hz, 2 H; o-H), 6.90 (br s, 2 H; o-H), 6.81 (t, J 7.7 Hz, 2 H; m-H), 6.72 (t, J 7.6 Hz, 2 H; m-H), 6.19 (m, 2 H, p; PhCH), 6.06 (t, J 7.1 Hz, 1 H; p-H), 3.57 (m, 4 H; THF), 1.89 (s, 3 H; Me), 1.73 (m, 4 H; THF), 0.96 (s, 18 H; tBu); 13 C NMR ([D 8 ]THF, 25 8C, 75.5 MHz): d 146.33 (qC), 145.78 (qC), 129.14 (oC), 129.09 (oC), 129.00 (oC), 128.70 (mC), 127.35 (mC), 127.32 (mC), 119.16 (PhCH), 115.81 (pC), 114.41 (PhCMe), 105.75 (pC), 37.5 (tBu), 12.35 (Me).
Crystallographic data for 1: Data collected on an Enraf Nonius Kappa CCD at 123 K. Crystal mounted under oil. C 31 H 48 NK 3 O 4 , M r 615.01, monoclinic, space group P2 1 /c (no. 14), red acicular crystal measuring 0.30 Γ 0.24 Γ 0.10 mm, a 10.7096(5), b 16.4210(8), c 19.8427(9) , b 91.875(2)8, V 3487.7(2) 3, Z 4, 1 calcd 1.171 g cm Γ3 , l(Mo Ka ) 0.71073 , m(Mo Ka ) 4.23 cm Γ1 , 42 594 reflections measured, 8661 unique, 3936 were observed (I > 3.00s(I)), R 0.043, R w 0.051, GoF 1.30. The structure was solved by direct methods with all H atoms placed in idealized positions (r 0.95 ). The aza-allylic anion is disordered in the crystal, as indicated by the occupancy of Me on C1 and C8 of 50:50.