Efficient and Selective Cleavage of t-Butoxycarbonyl Group from Carbamates and Amides by CeCl3·7H2O-NaI

J. S. Yadav; B. V. Subba Reddy; K. Srinivasa Reddy

doi:10.1055/s-2002-20467

LETTER

Efficient and Selective Cleavage of t-Butoxycarbonyl Group from Carbamates and Amides by CeCl₃·7H₂O-NaI

J. S. Yadav*, B. V. Subba Reddy, K. Srinivasa Reddy
Organic Chemistry Division-I, Indian Institute of Chemical Technology, Hyderabad-500 007, India
Fax: +91(40)7170512; e-Mail: yadav@iict.ap.nic.in;

Abstract

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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

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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.