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DOI: 10.1055/s-2004-815409
Synthesis of Sulfinimines by Direct Condensation of Sulfinamides with Aldehydes Using Cs2CO3 as an Activating and Dehydrating Reagent
Publication History
Publication Date:
12 January 2004 (online)
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Abstract
Chiral sulfinimines were prepared from chiral sulfinamides and aldehydes in CH2Cl2 in the presence of cesium carbonate as an amine-activating and dehydrating reagent.
Key words
sulfinimines - sulfinamides - cesium carbonate - dehydrations - amine activation
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References
At the reflux temperature of each solvent, considerable decomposition occurred (except CH2Cl2).
10Representative Experimental Procedure (Table 3, Entry 1): To a solution of 1 [5] (80.0 mg, 0.515 mmol) in CH2Cl2 (2.6 mL) were added Cs2CO3 (168 mg, 0.515 mmol) and benzaldehyde (0.0523 mL, 0.515 mmol). The resulting suspension was vigorously stirred at 40-45 °C for 8 h. The reaction mixture was filtered with Celite and the filter cake was washed with CH2Cl2. The filtrates and washings were combined and concentrated. The residue was chromatographed on silica gel (flash) with hexane-EtOAc = 9:1 to afford sulfinimine 6 (119 mg) in 95% yield. The ee of 6 was 97% determined by chiral HPLC analysis (Daicel Chiralcel OD column, 4.6 × 250 mm, 99.5:0.5 hexane-IPA; 1 mL/min, 254 nm, t R = 36.6 min; enantiomer of 6, t = 32.7 min), which was identical with that of 1 used (Daicel Chiralcel OD column, 4.6 × 250 mm, 90:10 hexane-IPA; 1 mL/min, 254 nm, t R = 18.0 min; enantiomer of 1, t R = 14.9 min). Compound 6: mp 78-79 °C (lit. [5a] [b] 77-78 °C, lit. [5c] 80-81 °C); [α]D 29 +114 (c 1.00, CHCl3) {lit. [5a] [α]D 20 +117.3 (c 1.77, CHCl3), lit. [5b] [α]D 20 +117.5 (c 1.6, CHCl3), lit. [5c] [α]D 20 +122.8 (c 1.2, CHCl3)}. 1H NMR (300 MHz, CDCl3, TMS = 0 ppm): δ = 2.40 (3 H, s), 7.32 (2 H, d, J = 8.0 Hz), 7.41-7.52 (3 H, m), 7.64 (2 H, d, J = 8.0 Hz), 7.82-7.87 (2 H, m), 8.75 (1 H, s). Sulfinimine 8 (Table [5] , entry 1) was obtained after silica-gel(flash) column chromatography (CH2Cl2) in 80% isolated yield by the same procedure as described above. The ee of 8 was 99% determined by chiral HPLC analysis (Daicel Chiralcel OD column, 4.6 × 250 mm, 95:5 hexane-IPA; 1 mL/min, 254 nm, t R = 5.51 min; enantiomer of 6, t R = 6.96 min), which was identical with that of 7 used (Daicel Chiralcel OD column, 4.6 × 250 mm, 96:4 hexane-IPA; 1 mL/min, 222 nm, t R = 41.6 min; enantiomer of 7, t R = 35.5 min). Compound 8: [α]D 28 +103 (c 1.00, CHCl3) {lit. [3] [α]D 20 +104 (c 1.00, CHCl3); enantiomer of 8, lit. [4c] [α]D 23 -122 (c 1.00, CHCl3)}. 1H NMR (300 MHz, CDCl3, TMS = 0 ppm): δ = 1.28 (9 H, s), 7.44-7.55 (3 H, m), 7.83-7.89 (2 H, m), 8.59 (1 H, s).