Compound 4a

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Compound data: 1H NMR

Compound data: 13C NMR

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

In a 15-mL scintillation vial, a mixture of 2a (33.6 mg, 50 µmol) and KHMDS (12.0 mg, 60 µmol) was chilled for 1 hour in a glovebox coldwell cooled with dry ice/acetone bath. Then, pre-cooled tert-butyl methyl ether (2.0 mL) was added, and the mixture was stirred with cooling for 10 minutes. ¹H NMR monitoring of the pale red solution using C₆D₆ as an internal locking solvent revealed immediate formation of 4a. After further stirring at room temperature for 3 hours, the pale red solution was passed through a glass filter, and evaporated to dryness. The obtained solid was dissolved into benzene, passed through a plug of Florisil, dried in vacuo at 120 °C overnight, to afford 4a as a colourless powder (22.0 mg, 25 µmol, quantitative yield). NOTE: Compound 4a is sensitive to oxygen. ¹H NMR (300 MHz, C₆D₆) δ 7.11–6.98 (m, 12H), 6.97–6.85 (m, 36H), 5.61 (s, 2H, NCH=CHN); ¹³C NMR (126 MHz, C₆D₆) δ 145.9 (4C, 4°), 145.0 (8C, 4°), 130.3 (16C, 3°), 127.7 (4C, 3°), 127.6 (16C, 3°), 126.7 (4C, 3°), 126.6 (4C, 3°), 124.7 (2C, 3°), 124.6 (2C, 3°), 114.6 (2C, NCH=CHN), 80.3 (4C, 4°); HRMS (m/z): [M+H]⁺ calcd. for C₆₆H₅₁N₂, 871.4047; found, 871.4028.