An Efficient Synthesis of Carborane Amines via One-Step Reaction of Carborane Triflates with N-Nucleophiles

Abstract

1-Trifluoromethanesulfonylmethyl-o-carborane and cesium 1-trifluoromethanesulfonylmethyl-1-carba-closo-dodecaborate react with amines in refluxing acetonitrile in the presence of NaOAc without a catalyst to give the corresponding amino derivatives. This approach allows for simple synthesis of neutral and anionic carborane amines not readily available via other synthetic routes.

Key words

carboranes - triflates - N-nucleophiles - amino carboranes

References and Notes

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11

General Procedure for the Synthesis of Amines 3a-e and 4a-c
A mixture of triflate 1 (1.0 g, 3.3 mmol), corresponding amine (3.3 mmol), and NaOAc (0.74 g, 9 mmol) in MeCN (10 mL) was refluxed for 4-8 h until the complete disap-pearance of 1 was proved by TLC (heptane-EtOAc, 7:3). Then the reaction mixture was poured into H₂O (20 mL) and extracted with EtOAc (3 × 7 mL). The organic layers were combined, washed with H₂O, and dried over MgSO₄. Then the mixture was filtered, and the solvent was removed under reduced air pressure. The residue was chromatographed on SiO₂ (eluent: heptane-EtOAc, 10:1) to afford the products as colorless solids.
Analytical Data for Compound 3a
Yield 76% (0.62 g); mp 92-93 ˚C. IR (KBr): 3392, 3069, 2595 cm^-¹. ^¹H NMR (400.13 MHz, CDCl₃): δ = 1.52-2.90 (m, 10 H), 3.77 (s, 1 H), 3.92 (d, J = 6.5 Hz, 2 H), 4.03 (s, 1 H), 7.24-6.60 (m, 5 H). ^¹¹B NMR (128.32 MHz, CDCl₃): δ = -2.32 (d, J = 149 Hz, 1 B), -5.20 (d, J = 149 Hz, 1 B),
-9.11 (d, J = 150 Hz, 2 B), -11.47 (d, J = 169 Hz, 2 B),
-12.96 (d, J = 149 Hz, 4 B). Anal. Calcd (%) for C₉H₁₉B₁₀N: C, 43.35; H, 7.63; N, 5.62. Found: C, 43.46; H, 7.81; N, 5.58.
Synthesis of Compound 5
To a stirred mixture of sodium amide prepared from sodium (0.16 g, 7.0 mmol) in liquid ammonia (50 mL), triflate 1 (2 g, 6.6 mmol) was added at -50 ˚C in anhyd toluene (10 mL). The reaction mixture was stirred at -50 ˚C for 1 h, then NH₄Cl (0.37 g, 7 mmol) was slowly added. The liquid ammonia was evaporated and H₂O (20 mL) was added. The product was extracted with EtOAc and dried over Na₂SO₄. The solvents were evaporated, and the crude product was purified by chromatography on SiO₂ (eluent: heptane) to afford 0.95 g (84% yield) of 5. White solid; mp 158 ˚C. ^¹H NMR (400.13 MHz, CDCl₃): δ = 1.20-3.10 (m, 10 H), 2.80 (s, 2 H), 3.89 (s, 1 H), 4.06 (s, 2 H). ^¹¹B NMR (128.32 MHz, CDCl₃): δ = -2.66 (d, J = 148 Hz, 1 B), -4.94 (d, J = 149 Hz, 1 B), -9.04 (d, J = 150 Hz, 2 B), -11.79 (d, J = 164 Hz, 2 B), -13.10 (d, J = 165 Hz, 4 B). Anal. Calcd (%) for C₃H₁₅B₁₀N: C, 20.81; H, 8.67; B, 62.43; N, 8.09. Found: C, 21.04; H, 8.57; B, 62.84; N, 8.15.

14

Synthesis of Compound 9 A mixture of triflate 2 (1.6 g, 3.6 mmol) and pyridine (0.28 g, 3.6 mmol) in CH₂Cl₂ (10 mL) was stirred at ambient temperature for 2 h. The solvent was removed to dryness in vacuo. The residue was washed with H₂O (15 mL), filtered off, and dried in vacuo to afford 0.81 g (94%) of 9. ^¹H NMR (400.13 MHz, CDCl₃): d = 1.10-2.50 (m, 11 H), 3.60 (s, 2 H), 8.33 (dd, J = 5.6, 7.6 Hz, 2 H), 8.87 (t, J = 7.6 Hz, 1 H), 9.17 (d, J = 5.6 Hz, 1 H). Anal. Calcd (%) for C₇H₁₈B₁₁N: C, 35.78; H, 7.67; B 50,60, N, 5.96. Found: C 35.22; H, 7.53; B, 51.02, N, 6.11.