Alkoxyamines by Reaction of 2,2,6,6-Tetramethylpiperidine-1-oxoammonium Tetrafluoroborate with Enolates

Abstract

Alkoxyamines are prepared from the oxoammonium salt of TEMPO and enolates in one step and metal free in 47-89% yield. One of these alkoxyamines (6b) was used to polymerize styrene with a polydispersity index (PDI) = 1.42 (125 °C) and 1.49 (105 °C).

Key words

alkoxyamines - radical reaction - polymerization - ­alkylation - oxoammonium salt

References

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  A. Studer, University of Münster, personal communication.

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We thank the Degussa AG Hüls for a research sample of TEMPO.

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General Procedure for the Preparation of 6a,b,d-f: Sodium hydride (124 mg, 3.10 mmol) was stirred with 3.0 mmol of 4 in 8 mL anhyd THF at 0 °C. Compound 4g was deprotonated at -78 °C and LDA was used instead of sodium hydride. When the hydrogen evolution had ceased, the suspension was warmed up to r.t. and 781 mg (3.2 mmol) of 2 [18] were added. After stirring for 2 h, 1.5 mL H₂O were added and the organic phase was separated. The aq phase was washed with Et₂O (2 × 10 mL) and the combined organic phase was dried over MgSO₄. The Et₂O was evaporated and the crude product was purified by flash chromatography.
Compounds 6a,b,d-g were characterized by ¹H NMR (300 MHz, CDCl₃) and ¹³C NMR (75 MHz, CDCl₃), MS and elemental analysis.
6a: ¹H NMR: δ = 1.00-1.07 (m, 6 H, 2 × CH₃), 1.20 (s, 6 H, 2 × CH₃), 1.28 (t, J = 7.0 Hz, 3 H, CH₂ CH ₃ ), 1.46 (s, 6 H, 3 × CH₂), 2.30 (s, 3 H, CH₃), 4.20 (q, 2 H, OCH₂), 4.80 (s, 1 H, 2-H) ppm. ¹³C NMR: δ = 12.9 (q, CH₂ CH ₃ ), 15.8 (t, CH₂), 19.0 (2 q, CH₃), 25.3 (q, C-4), 31.4, 31.8 (2 q, CH₃), 38.9 (2 t, CH₂), 58.9 [2 s, C(CH₃)₂], 60.3 (t, OCH₂), 92.5 (d, C-2), 166.6 (s, C-1), 201.5 (s, C-3) ppm. MS (ESI, ES+): m/z (%) = 286 (77) [M + H⁺], 142 (20) [C₁₉H₁₈NH₂ ⁺], 141 (100) [C₉H₁₉N⁺], 126 (76) [C₉H₁₈ ⁺], 61 (17). Anal. Calcd for C₁₅H₂₇NO₄ (285.38): C, 63.13; H, 9.54; N, 4.91. Found: C, 63.03; H, 9.61; N, 4.94.
6b: Mp: 29-30 °C. R_f = 0.09 (PE-Et₂O 20:1). ¹H NMR: δ = 1.01, 1.20 (2 s, 12 H, 4 × CH₃), 1.26-1.31 (m, 6 H, 2 × CH₃), 1.42-1.46 (m, 6 H, 3 × CH₂), 4.17-4.30 (m, 4 H, 2 × OCH₂), 4.92 (s, 1 H, 2-H) ppm. ¹³C NMR: δ = 13.2 (2 q, CH₂ CH ₃), 16.1 (t, CH₂), 19.3 (2 q, CH₃), 31.7 (2 q, CH₃), 39.4 (2 t, CH₂), 59.4 [2 s, C(CH₃)₂], 60.7 (2 t, OCH₂), 86.0 (d, C-2), 166.4 (2 s, C-1, C-3) ppm. MS (ESI, ES+): m/z (%) = 316 (15) [M + H⁺], 192 (35), 141 (22) [C₉H₁₉N⁺], 126 (100) [C₉H₁₈]. Anal. Calcd for C₁₆H₂₉NO₅ (315.40): C, 60.93; H, 9.27; N, 4.44. Found: C, 61.01; H, 9.42; N, 4.40.
6d: R_f = 0.07 (PE-Et₂O 20:1). Mp 54-55 °C. ¹H NMR:
δ = 0.98 (s, 6 H, 3 × CH₂), 2.21 (2 s, 6 H, 1-H, 5-H), 4.92 (s, 1 H, 3-H), 1.20 (s, 6 H, 3 × CH₂), 1.45 (s, 6 H, 3 × CH₂) ppm. ¹³C NMR: δ = 16.8 (t, CH₂), 20.0 (2 q, CH₃), 26.9 (2 q, C-1, C-5), 32.8 (2 q, CH₃), 40.3 (2 t, CH₂), 59.9 [2 s, C(CH₃)₂], 101.4 (d, C-3), 203.6 (2 s, C-2, C-4) ppm. MS (ESI, ES+): m/z (%) = 256 (24) [M + H⁺], 156 (2) [C₉H₁₈N=O⁺], 142 (30) [C₉H₁₈NH₂ ⁺], 141 (97) [C₉H₁₉N⁺], 126 (100) [C₉H₁₈ ⁺], 70 (4), 60 (25), 43 (8) [CH₃CO⁺]. Anal. Calcd for C₁₄H₂₅NO₃ (255.35): C, 65.85; H, 9.87; N, 5.49. Found: C, 65.71; H, 9.98; N, 5.29.
6e: R _f = 0.22 (PE-Et₂O 10:1). Mp 63 °C. ¹H NMR: δ = 0.83, 0.99 (2 s, 6 H, 2 × CH₃), 1.13 (t, J = 7.1 Hz, 3 H, CH₂ CH ₃), 1.18, 1.29 (2 s, 6 H, 2 × CH₃), 1.40-1.48 (m, 6 H, 3 × CH₂), 4.16 (q, 2 H, OCH₂), 5.41 (s, 1 H, 2-H), 7.43-7.60 (m, 3 H, CH_arom.), 8.13-8.16 (m, 2 H, CH_arom.) ppm. ¹³C NMR: δ = 13.9 (q, CH₂ CH ₃), 17.0 (t, CH₂), 20.2 (2 q, CH₃), 32.5, 33.1 (2 q CH₃), 40.1 (2 t, CH₂), 60.0, 60.4 [2 s, C(CH₃)₂], 61.6 (t, OCH₂), 92.9 (d, C-2), 128.4, 129.8, 133.5, (5 d, CH_arom.), 134.6 (s, C_arom.), 168.2 (s, C-1), 193.6 (s, C-3) ppm. MS (ESI, ES+): m/z (%) = 348 (38) [M + H⁺], 246 (5), 243 (12), 156 (8) [C₉H₁₈N=O⁺], 141 (75) [C₉H₁₉N⁺], 126(55) [C₉H₁₈ ⁺], 122 (50), 105 (100) [C₆H₅CO⁺]. Anal. Calcd for C₂₀H₂₉NO₄ (347.45): C, 69.14; H, 8.41; N, 4.03. Found: C, 69.16; H, 8.31; N, 3.91.
6f: R _f = 0.18 (PE-Et₂O 15:1). Mp 67 °C. ¹H NMR: δ = 0.83 (s, 3 H, CH₃), 1.06 (s, 6 H, 2 × CH₃), 1.26 (s, 3 H, CH₃), 1.40-1.47 (m, 6 H, 3 × CH₂), 2.24 (s, 3 H, 4-H), 5.59 (s, 1 H, 2-H), 7.43-7.59 (m, 3 H, CH_arom.), 8.03-8.10 (m, 2 H, CH_arom.) ppm. ¹³C NMR: δ = 16.9 (t, CH₂), 20.2, 20.3 (2 q, CH₃), 26.7 (q, C-4), 32.8, 33.0 (2 q, CH₃), 40.2 (2 t, CH₂), 60.0, 60.2 [2 s, C(CH₃)₂], 100.1 (d, C-2), 128.6, 129.9, 133.8, (5 d, CH_arom.), 134.6 (s, C_arom.), 195.3 (s, C-1), 203.5 (s, C-3) ppm. MS (ESI, ES+): m/z (%) = 318 (60) [M + H⁺], 276 (3) [M + H⁺ - OCCH₂], 246 (2), 184 (4), 156 (3) [C₉H₁₈N=O⁺], 141 (100) [C₉H₁₉N⁺], 126 (80) [C₉H₁₈ ⁺], 122 (30), 105 (100) [C₆H₅CO⁺], 60 (10). Anal. Calcd for C₁₉H₂₇NO₃ (317.42): C, 71.89; H, 8.57; N, 4.41. Found: C, 72.00; H, 8.56; N, 4.04.
6g: R_f = 0.30 (CH-EtOAc, 10:1). Mp 27 °C. ¹H NMR (400 MHz, CDCl₃): δ = 1.00-1.01 (m, 6 H, 2 × CH₃), 1.11-1.17 (m, 6 H, 2 × CH₃), 1.32-1.53 (m, 6 H, 3 × CH₂), 1.56-1.64 (m, 1 H, 4-H), 1.71-1.81 (m, 1 H, 5-H), 1.84-2.04 (m, 3 H, 3-H, 4-H, 5-H), 2.08-2.16 (m, 1 H, 3-H), 2.23-2.29 (m, 1 H, 6-H), 2.73-2.80 (m, 1 H, 6-H), 4.14-4.17 (m, 1 H, 2-H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 17.1 (t, CH₂), 20.1 (2 q, CH₃), 22.0 (t, C-4), 28.4 (t, C-5), 34.8 (t, C-3), 33.5, 33.9 (2 q, CH₃), 40.2 (2 t, CH₂), 40.9 (t, C-6), 59.7 [2 s, C(CH₃)₂], 89.2 (d, C-2), 211.5 (s, C-1) ppm. MS (ESI, ES+): m/z (%) = 254 (100) [M + H⁺], 142 (55) [C₉H₁₈NH₂ ⁺], 126 (92) [C₉H₁₈ ⁺], 113 (30) [M + H⁺ - C₉H₁₉N], 85 (28) [113 - CO], 67 (80). Anal. Calcd for C₁₅H₂₇NO₂ (253.38): C, 71.10; H, 10.74; N, 5.53. Found: C, 70.96; H, 11.02; N, 5.39.
Monodeacetylated dehydrodimer of 5d: MS (ESI, ES⁺): m/z (%) = 155 (7) [M + H⁺]; Monodeacetylated dehydrodimer of 5f: MS (ESI, ES⁺): m/z (%) = 279 (5) [M + H⁺].

23

We thank the Zentrale Forschung der Bayer AG, Krefeld for the molecular weight determination.