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DOI: 10.1055/s-2002-20467
Efficient and Selective Cleavage of t-Butoxycarbonyl Group from Carbamates and Amides by CeCl3·7H2O-NaI
Publikationsverlauf
Publikationsdatum:
05. Februar 2007 (online)
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Abstract
A highly selective cleavage of the t-butoxycarbonyl group has been achieved in high yields using CeCl3·7H2O-NaI in acetonitrile at ambient temperature under neutral conditions. This method is mild and compatible with a wide range of functional groups such as THP, TBDMS, TBDPS, trityl ethers, mono-BOC or Cbz protected amines, acetamide, sulfonamide and benzamide etc., present in the substrate.
Key words
cerium reagents - carbamates - amides - α-amino acids
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References
Experimental Procedure: A mixture of di-BOC derivative (5 mmol), CeCl3·7 H2O (5 mmol) and sodium iodide (5 mmol) in acetonitrile (10 mL) was stirred at ambient temperature for an appropriate time (Table). After complete conversion, as indicated by TLC, the reaction mixture was diluted with water (25 mL) and extracted with ethyl acetate (2 × 20 mL). The combined organic layers were washed with brine, dried over anhyd Na2SO4 and concentrated in vacuo, and the resulting product was purified by column chromatography on silica gel (Merck, 100-200 mesh, ethyl acetate-hexane, 2:8) to afford pure mono-BOC protected amine. Spectroscopic Data of 1a: [α]D 25 = -38.2 (c 1.5, CHCl3). 1H NMR (CDCl3): δ = 1.45 (s, 18 H), 3.60 (dd, 2 H, J = 5.5, 13.6 Hz), 3.65 (s, 3 H), 5.38 (dd, 1 H, J = 5.5, 10.3 Hz), 7.28-7.42 (m, 15 H). 2a: [α]D 25 = +11.3 (c 1.5, CHCl3). 1H NMR (CDCl3): δ = 1.40 (s, 9 H), 3.38 (dd, 2 H, J = 5.5, 13.6 Hz), 3.75 (s, 3 H), 4.38 (m, 1 H), 5.35 (brd, NH, J = 8.0 Hz), 7.10-7.40 (m, 15 H). 1b: [α]D 25 = -29.789 (c 1.5, CHCl3). 1H NMR (CDCl3): δ = 0.03 (s, 6 H), 0.85 (s, 9 H), 1.48 (s, 18 H), 3.67 (s, 3 H), 4.10 (dd, 2 H, J = 5.8, 13.7 Hz), 5.10 (dd, 1 H, J = 5.8 and 10.5 Hz). 2b: [α]D 25 = +17.684 (c 1.5, CHCl3). 1H NMR (CDCl3): δ = 0.02 (s, 6 H), 0.84 (s, 9 H), 1.43 (s, 9 H), 3.75 (s, 3 H), 3.80 (dd, 1 H, J = 5.8, 13.7 Hz), 4.05 (dd, 1 H, J = 5.8, 13.7 Hz), 4.30 (m, 1 H), 5.23 (brd, NH, J = 7.8 Hz). 1d: [α]D 25 = -11.8 (c 1.5, CHCl3). 1H NMR (CDCl3): δ = 1.03 (s, 9 H), 1.43 (s, 18 H), 3.62 (s, 3 H), 4.18 (dd, 2 H, J = 5.7, 13.8 Hz), 5.23 (dd, 1 H, J = 5.7, 10.3 Hz), 7.38-7.40 (m, 6 H), 7.58-7.65 (m, 4 H). 2d: [α]D 25 = +14.2 (c 1.5, CHCl3). 1H NMR (CDCl3): δ = 1.0 (s, 9 H), 1.45 (s, 9 H), 3.78 (s, 3 H), 3.98 (dd, 2 H, J = 5.7, 13.8 Hz), 4.38 (m, 1 H), 5.32 (br d, NH, J = 8.3 Hz), 7.28-7.43 (m, 6 H), 7.5-7.63 (m, 4 H). 1h: [α]D 25 = -35.57 (c 1.0, CHCl3). 1H NMR (CDCl3): δ = 1.48 (s, 18 H), 2.10 (s, 3 H), 2.43-2.60 (m, 4 H), 3.78 (s, 3 H), 5.05 (dd, 1 H, J = 9.0 and 4.5 Hz). 2h: [α]D 25 = 24.3 (c 2.8, CHCl3), (ref. [5] [α]D 25 = 24.6 (c 2.84, CHCl3)). 1H NMR (CDCl3): δ = 1.33 (s, 9 H), 1.78-1.90 (m, 2 H), 1.98 (s, 3 H), 2.41 (t, 2 H, J = 7.3 Hz), 3.65 (s, 3 H), 4.32-4.41 (m, 1 H), 5.23 (br s, NH). 1j: [α]D 25 = +12.8 (c 1.0, CHCl3). 1H NMR (CDCl3): δ = 0.88 (d, 3 H, J = 6.8 Hz), 1.18 (d, 3 H, J = 6.8 Hz), 1.50 (s, 18 H), 2.42-2.50 (m, 1 H), 3.78 (s, 3 H), 4.48 (d, 1 H, J = 6.8 Hz). 2j: [α]D 25 = -20.8 (c 1.1, MeOH) (ref. [5] [α]D 25 = -21.2 (c 1.1, MeOH)). 1H NMR (CDCl3): δ = 0.85 (d, 3 H, J = 6.8 Hz), 0.90 (d, 3 H, J = 6.8 Hz), 1.50 (s, 9 H), 2.02-2.18 (m, 1 H), 3.75 (s, 3 H), 4.23 (m, 1 H), 4.95 (brs, NH). 1l: [α]D 25 = -37.2 (c 2.15, CHCl3), (ref. [5] [α]D 25 = -37.2 (c 2.15, CHCl3)). 1H NMR (CDCl3): δ = 1.50 (s, 18 H), 2.18 (m, 1 H), 2.40 (m, 2 H), 2.45 (m, 1 H), 3.68 (s, 3 H), 3.75 (s, 3 H), 4.95 (dd, 1 H, J = 9.0 and 4.3 Hz). 2l: [α]D 25 = +12.7 (c 2.00, CHCl3), [ref. [5] [α]D 25 = +12.9 (c 2.00, CHCl3)]. 1H NMR (CDCl3): δ = 1.40 (s, 9 H), 1.90 (m, 1 H), 2.15 (m, 1 H), 2.39 (m, 2 H), 3.65 (s, 3 H), 3.70 (s, 3 H), 3.40 (br s, 1 H), 5.15 (br s, NH). IICT Commun. No: 01/x/10.