Compound (±)-3b

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InChIKey GEXVYJRHSCVHHT-UHFFFAOYSA-N

Synthetic procedure: See article for the definitive version of this procedure and for full experimental details.

By analogy to a literature procedure, a flame-dried Schlenk flask equipped with a magnetic stir bar and an argon inlet was evacuated and backfilled with argon (2 ×). The flask was charged with (±)-dimethyl BINAM ((±)-S2) (960 mg, 3.07 mmol) and THF (20.5 mL), and the solution was cooled to –72 °C (internal temperature) using a dry-ice/acetone bath. n-BuLi (1.55 M solution in hexane, 4.00 mL, 6.20 mmol, 2.02 equiv) was added dropwise over 10 min yielding a yellow-black suspension. The mixture was warmed to 22 °C (internal temperature), stirred at this temperature for 30 min and cooled again to –72 °C. To the cooled mixture was added a freshly prepared solution of i-Pr₂N–PCl₂⁵ (655 mg, 3.24 mmol, 1.06 equiv) and THF (5.2 mL) dropwise over 10 min and the mixture was warmed to 22 °C. After 45 min, sulfur powder (296 mg, 9.23 mmol, 3.00 equiv) was added at room temperature and stirring under argon was continued for 52 h. The resulting brown solution was filtered through a pad of Celite^®, which was rinsed with EtOAc (100 mL). The filtrate was concentrated in vacuo (20–23 °C, 20 mmHg) yielding a brown solid. Purification by flash column chromatography (SiO₂, 140 g, 45 mm Ø hexane/Et₂O = 60:1→30:1) afforded an off-white solid (671 mg), which was recrystallized from EtOAc/hexane to give (±)-3b (616 mg, 42%) as a white, crystalline compound. Traces EtOAc could not be removed from the product even when using Abderhalden's drying pistol. The product was dissolved in a minimal amount of benzene and EtOAc was removed azeotropically. Traces benzene (4%) could not be removed from the product. mp: 272–274 °C (benzene); ¹H NMR: (500 MHz, CDCl₃) δ 7.99 (d, J = 8.9 Hz, 1H, HC(4,4')), 7.92 (d, J = 8.9 Hz, 1H, HC(4',4)), 7.90 (d, J = 8.5 Hz, 1H, HC(6)), 7.87 (d, J = 8.1 Hz, 1H, HC(6)), 7.70 (d, J = 8.8 Hz, 1H, HC(3)), 7.66 (d, J = 9.0 Hz, 1H, HC(3')), 7.42 (t, J = 7.2 Hz, 1H, HC(7)), 7.35 (t, J = 7.2 Hz, 1H, HC(7')), 7.29 (d, J = 8.5 Hz, 1H, HC(9)), 7.23 (ddd, J = 8.4, 6.7, 1.3 Hz, 1H, HC(8)), 7.11 (ddd, J = 8.4, 6.9, 1.4 Hz, 1H, HC(8')), 6.98 (d, J = 8.6 Hz, 1H, HC(9')), 3.57–3.34 (m, 2H, HC(12), HC(12')), 3.28 d, J = 11.7 Hz, 3H, HC(11)), 3.12 d, J = 13.3 Hz, 3H, HC(11')), 1.67–1.00 (br, 12H, HC(13), HC(13'), HC(14), HC(14')); ¹³C NMR: (125 MHz, CDCl₃) d 143.7 (δ, J = 4.4 Hz, C(2,2')), 142.3 (d, J = 2.0 Hz, C(2',2)), 132.7 (C(aryl)), 132.3 (C(aryl)), 131.3 (C(aryl)), 130.6 (C(aryl)), 129.1 (C(4,4')), 128.3 (C(4',4)), 128.2 (C(6,6')), 128.1 (C(6',6)), 127.73 (C(9)), 127.67 (d, J = 2.5 Hz, C(1,1')), 127.62 (d, J = 3.9 Hz, C(1',1)), 127.4 (C(9')), 125.9 (C(8)), 125.6 (C(8')), 124.9 (C(7)), 124.7 (C(7')), 122.8 (d, J = 2.1 Hz, C(3,3')), 122.5 (C(3',3)), 47.6 (br, C(12), C(12')), 36.8 (d, J = 11.1 Hz, C(11,11')), 36.3 (d, J = 5.3 Hz, C(11',11)), 24.7 (C(13,13')), 22.3 (br, C(14,14')); ³¹P NMR: (202 MHz, CDCl₃) 82.5; IR: 2975 (w), 2924 (w), 1616 (w), 1593 (w), 1505 (w), 1465 (w), 1407 (w), 1363 (w), 1326 (w), 1277 (w), 1259 (w), 1244 (w), 1177 (m), 1143 (m), 1117 (m), 1086 (m), 1025 (w), 1002 (w), 988 (s), 932 (s), 921 (s), 851 (m), 815 (s), 747 (s), 703 (s), 678 (s); MS: (ESI) 474 (M+H); HRMS: calcd for C₂₈H₃₃N₃PS⁺: 474.2133, found: 474.2130; TLC: Rf 0.42 (hexanes/EtOAc, 10:1); Analysis: C28H32N3PS (473.62); Calcd: C, 71.01; H, 6.81; N, 8.87 Found: C, 71.21; H, 6.84; N, 8.62