Abstract
The syntheses of new chiral cyclic 1,2-diacetals from (2R, 3R)-( )-tartaric acid are described. C(2)-symmetrical diamines were prepared via direct amidation of the tartrate or from the corresponding bismesylate via reaction with sodium azide. For C1-symmetrical compounds, the Appel reaction was used to form the key intermediate, a monochlorocarbinol, from the diol. Some of the new chiral compounds, produced in good to high yields, may be potentially useful as asymmetric organocatalysts or as nitrogen and sulfur chelating ligands for asymmetric metal catalyzed reactions. Thus, a bis-N-methyl-methanamine derivative, used in substoichiometric amounts, was found to catalyze the enantioselective addition of cyclohexanone to (E)-beta-nitrostyrene with high diastereoselectivity (syn / anti = 92:8), albeit giving moderate optical purity (syn: 30 %).
Highlights
Chiral amines chelated to metals are used in medicines, they are used as chiral auxiliaries in stereoselective synthesis and as metal ligands in catalytic asymmetric synthesis [2]
Tartaric acid is an example of such a synthon, and we have recently developed novel oxazoline carbinols A [3] and bis(oxazolines) B [4] based on this starting material and applied them in enantioselective metal-catalyzed processes
The acid was converted by a known procedure into cyclic bisacetal ester 1 [15], from which all the ligands were synthesized.To prepare a C2-symmetrical tosylated diamine, a diazide was chosen as intermediate (Scheme 1)
Summary
Evaporation of the solvent gave a clear colourless liquid (0.604 g, 84 %), which was used in the reaction without further purification; for elemental analysis, the product was purified by preparative chromatography on silica gel (1:4 EtOAc-hexane): [α]26D = –102.7 (c 2.00, CHCl3); 1H-NMR: δ 1.33 (s, 3 H, 2 × CH3), 3.21 (br d, 2 H, J = 12.8 Hz, CH2), 3.31 (s, 3 H, OCH3), 3.31–3.38 (m, 2 H, CH2), 3.87–3.88 (m, 2 H, 2 × CH) ppm; 13C-NMR: δ 17.3 (2 × CH3), 48.1 (2 × OCH3), 50.8 (2 × CH2), 69.0 (2 × CH), 99.1 (2 × acetal-C) ppm; IR: v~ (CHCl3) 3009, 2948, 2932, 2837, 2103, 1444, 1379, 1294, 1253, 1229, 1143, 1133, 1037, 962, 909, 862, 651, 559 cm-1; MS (EI) m/z (%): 271 (M+-15, 0.12), 255 (0.33), 197 (46), 116 (55), 101 (99), 95 (29), 89 (23), 84 (11), 82 (30), 81 (89), 76 (99.8), 75 (96), 73 (100), 70 (11), 69 (22), 68 (44), 67 (88), 59 (36), 57 (19), 56 (20), 55 (62), 54 (95), 53 (11); Anal.
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