Palladium-Catalyzed Cross-Coupling Reactions of 2-Pyridylborates with Air-Stable HASPO Preligands

Abstract

A novel, air-stable TADDOLP(O)H derivative bearing electron-withdrawing substituents allows for efficient Suzuki-Miyaura cross-couplings with challenging electron-deficient 2-pyr-idylborates as nucleophiles.

borates - cross-coupling - heteroarenes - palladium - pyr-idines

References and Notes

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<A NAME="RG23009ST-24">24</A>

Analytical Data for HASPO 6d: Mp 202.9-203.4 ˚C. ^¹H NMR (300 MHz, CDCl₃): δ = 7.67-7.45 (m, 6 H), 7.19-7.15 (m, 2 H), 6.94-6.78 (m, 8 H), 6.89 (d, J _H-P = 744 Hz, 1 H), 5.67 (d, J = 8.3 Hz, 1 H), 5.18 (d, J = 8.3 Hz, 1 H), 0.71 (s, 3 H), 0.68 (s, 3 H). ^¹³C NMR (75 MHz, CDCl₃): δ = 162.5 (C_q, ^¹ J _F-C = 248 Hz), 162.5 (C_q, ^¹ J _F-C = 248 Hz), 162.3 (C_q,  ^¹ J _F-C = 248 Hz), 162.3 (C_q, ^¹ J _F-C = 248 Hz), 139.3 (C_q, ⁴ J _F-C = 3 Hz), 139.3 (C_q, ⁴ J _F-C = 3 Hz), 138.7 (C_q, ⁴ J _F-C =
3 Hz), 134.5 (C_q, ⁴ J _F-C = 3 Hz), 130.7 (CH, ^³ J _F-C = 8 Hz), 130.0 (CH, ^³ J _F-C = 8 Hz), 128.6 (CH, ^³ J _F-C = 8 Hz), 128.6 (CH, ^³ J _F-C = 8 Hz), 115.6 (CH, ^² J _F-C = 21 Hz), 115.4 (CH, ^² J _F-C = 22 Hz), 114.6 (C_q), 114.5 (CH, ^² J _F-C = 22 Hz), 114.3 (CH, ^² J _F-C = 22 Hz), 88.7 (C_q), 87.6 (C_q), 80.0 (CH), 79.5 (CH), 26.8 (CH₃), 26.6 (CH₃). ^³¹P NMR (121 MHz, CDCl₃): δ = -2.5. ^¹9F NMR (282 MHz, CDCl₃): δ = -112.4 (m),
-112.9 (m), -113.9 (m), -114.1 (m). IR (KBr): 3424, 2993, 2903, 2354, 2344, 1601, 1506, 1268, 1161, 1082, 937, 847, 762 cm^-¹. HR-MS (ESI): m/z calcd for C₃₁H₂₄F₄O₅P: 583.1303; found: 583.1306.

<A NAME="RG23009ST-25">25</A>

Synthesis of 3b (Table  [²] , entry 1); Typical procedure: A suspension of Pd₂dba₃ (4.6 mg, 0.005 mmol, 1.0 mol%), 6d (11.7 mg, 0.020 mmol, 4.0 mol%), K₃PO₄ (318 mg, 1.50 mmol), 1a (205 mg, 0.75 mmol), 2b (147 mg, 0.50 mmol) in 1,4-dioxane (2.0 mL) was stirred under N₂ for 20 h at 110 ˚C. After the reaction mixture was cooled to ambient temperature, MTBE (50 mL) and H₂O (50 mL) were added. The separated aqueous phase was extracted with MTBE (3 × 50 mL). The combined organic layers were washed with brine (50 mL), dried over Na₂SO₄ and concentrated in vacuo. The remaining residue was purified by column chromatog-raphy on silica gel (n-hexane-EtOAc, 9:1) to yield 3b (114 mg, 78%) as a white solid (mp 45.0 ˚C). ^¹H NMR (300 MHz, CDCl₃): δ = 8.75 (dt, J = 4.8, 1.4 Hz, 1 H), 8.48 (s, 2 H), 7.91 (s, 1 H), 7.88-7.77 (m, 2 H), 7.40-7.29 (m, 1 H). ^¹³C NMR (75 MHz, CDCl₃): δ = 154.1 (C_q), 150.1 (CH), 141.3 (C_q), 137.2 (CH), 132.1 (C_q, ^² J _F-C = 33 Hz), 126.9 (CH, ^³ J _F-C =
4 Hz), 123.6 (CH), 123.4 (C_q, ^¹ J _F-C = 273 Hz), 122.3 (CH, ^³ J _F-C = 4 Hz), 120.6 (CH). ^¹9F NMR (282 MHz, CDCl₃): δ = -62.9. IR (KBr): 3897, 2927, 1591, 1455, 1382, 1279, 1136, 897, 785, 683 cm^-¹. MS (EI): m/z (%) = 291 (100) [M⁺], 272 (22), 252 (10), 222 (38), 202 (12), 83 (28), 71 (34), 57 (66), 43 (64). HR-MS (EI): m/z calcd for C₁₃H₇F₆N: 292.0555; found: 292.0557. The spectral data were in accordance with those reported in the literature.^¹6