DMAP-Catalyzed Benzannulation of Ethyl Propiolate with β-Dicarbonyl Moieties

Abstract

4-Dimethylaminopyridine (DMAP)-catalyzed benzannulation reaction of ethyl propiolate with β-dicarbonyl compounds at room temperature providing highly substituted benzenes is ­described.

Key words

ethyl propiolate - DMAP - benzannulation - β-dicarbonyl compounds

References and Notes

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12

Typical Procedure: A round-bottomed flask, equipped with a stirring bar, was charged with β-dicarbonyl moieties (0.3 mmol) and DMAP (0.06 mmol) in CH₂Cl₂ (3 mL) followed by ethyl propiolate (0.66 mmol) via a syringe. After stirring for the specific time at r.t., the reaction was concentrated under reduced pressure on a rotary evaporator and purified by silica gel chromatography using PE-EtOAc (10:1-5:1) to afford the corresponding product. Compound 3a: ¹H NMR (300 MHz, CDCl₃): δ = 8.39 (d, J = 1.7 Hz, 1 H), 8.18 (d, J = 1.7 Hz, 1 H), 4.30-4.39 (m, 4 H), 2.57 (s, 3 H), 2.55 (s, 3 H), 1.37 (t, J = 7.8 Hz, 6 H). ¹³C NMR (75 Hz, CDCl₃): δ = 202.3, 167.2, 165.2, 142.1, 141.8, 133.7, 132.7, 130.9, 128.2, 61.71, 61.68, 30.7, 18.2, 14.4, 14.3. IR (neat): 1725, 1259 cm^-1. HRMS (ESI): m/z [M⁺] calcd for C₁₅H₁₈O₅: 278.1154; found: 278.1147.
Compound 7a: ¹H NMR (300 MHz, CDCl₃): d = 8.01 (d, J = 15.8 Hz, 1 H), 7.69 (s, 1 H), 7.55 (d, J = 7.9 Hz, 2 H), 7.34-7.43 (m, 4 H), 5.84 (dd, J = 3.2, 10.2 Hz, 1 H), 4.23-4.35 (m, 4 H), 4.15-4.19 (m, 2 H), 2.86 (dd, J = 10.2, 15.2 Hz, 1 H), 2.54 (dd, J = 3.2, 15.2 Hz, 1 H), 1.31-1.41 (m, 6 H), 1.24 (t, J = 7.2 Hz, 3 H). ¹³C NMR (75 MHz, CDCl₃): d = 169.6, 165.0, 164.3, 162.1, 140.0, 136.0, 132.6, 129.9, 129.0, 128.2, 120.0, 117.9, 105.6, 71.9, 60.96, 60.92, 60.88, 37.8, 14.53, 14.45, 14.39. HRMS (EI): m/z [M⁺] calcd for C₂₃H₂₆O₇: 414.1679; found: 414.1674.
Compound 10a: ¹H NMR (300 MHz, CDCl₃): δ = 9.20 (d, J = 1.8 Hz, 1 H), 8.55 (d, J = 1.8 Hz, 1 H), 7.30 (m, 1 H), 7.12-7.17 (m, 2 H), 6.97-7.06 (m, 4 H), 6.87 (d, J = 7.5 Hz, 2 H), 4.49 (q, J = 7.2 Hz, 2 H), 3.99 (q, J = 7.2 Hz, 2 H), 2.33 (s, 3 H), 1.48 (t, J = 7.2 Hz, 3 H), 0.87 (t, J = 7.2 Hz, 3 H). ¹³C NMR (75 Hz, CDCl₃): δ = 166.7, 164.4, 144.8, 143.9, 142.1, 137.3, 136.6, 134.6, 134.2, 131.8, 130.5, 130.1, 129.2, 128.2, 127.9, 127.1, 62.1, 61.7, 21.6, 14.4, 13.6. IR (neat): 1727, 1248 cm^-1. HRMS (EI): m/z [M⁺] calcd for C₂₅H₂₄O₆S: 452.1294; found: 452.1302.