Thermal and Au(I)-Catalyzed Intramolecular [4+2] Cycloaddition of Aryl-Substituted 1,6-Diynes for the Synthesis of Biaryl Compounds

Abstract

1,6-Diynes, possessing aryl groups on their termini, undergo an intramolecular [4+2] cycloaddition via strained cyclic allene intermediates to give various biaryl compounds. Under thermal conditions, isomerization of the intermediates occurs, while, in the presence of a cationic gold catalyst, skeletal rearrangement is a ­major pathway.

Key words

cycloaddition - diynes - arylalkynes - gold - biaryl compounds

References

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10

Typical experimental procedure for the Au(I)-catalyzed cycloaddition (Table [2] , entry 7): AuCl(PPh₃) (1.0 mg, 0.0020 mmol) was placed in a flask, and a CH₂Cl₂ solution (8 mL) of diyne 1a (34.8 mg, 0.10 mmol) was added. To the resulting mixture was added AgSbF₆ (0.8 mg, 0.0024 mmol), and the mixture was stirred at 0 °C for 5 h. The reaction was quenched by the addition of H₂O (20 mL) and organic materials were extracted with CH₂Cl₂. The combined organic layer was dried over Na₂SO₄. The solvent was removed under reduced pressure, and the residue was purified by TLC to give products 2a (3.1 mg, 9%) and 3a (24.0 mg, 69%). 2a: Yellow oil; IR (neat): 825, 795, 775, 750, 739 cm^-1; ¹H NMR (400 MHz, CDCl₃): δ = 2.01-2.15 (m, 2 H), 2.49-2.59 (m, 1 H), 2.67-2.77 (m, 1 H), 3.23-3.27 (m, 2 H), 7.19-7.30 (m, 3 H), 7.41-7.47 (m, 3 H), 7.50-7.54 (m, 1 H), 7.57-7.64 (m, 1 H), 7.77 (d, 1 H, J = 8.0 Hz), 7.93 (d, 2 H, J = 8.0 Hz), 8.68 (s, 1 H), 8.75 (d, 1 H, J = 8.4 Hz); ¹³C NMR (75 MHz, CDCl₃): δ = 25.6, 32.3, 33.6, 100.5, 117.2, 122.6, 125.0, 125.5, 125.6, 125.8, 126.0, 126.1, 126.2, 127.4, 127.6, 128.2, 128.3, 129.5, 130.1, 130.4, 131.4, 132.3, 133.6, 133.7, 137.4, 143.2, 143.2; HRMS (FAB): m/z calcd for C₂₇H₂₀ (M⁺): 344.1565, found: 344.1562. 3a: Yellow oil; IR (neat) 823, 796, 779, 739
cm^-1; ¹H NMR (400 MHz, CDCl₃): δ = 1.89-1.95 (m, 2 H), 2.50-2.63 (m, 2 H), 2.66-2.70 (m, 2 H), 7.04 (d, 1 H, J = 8.4 Hz), 7.31-7.40 (m, 2 H), 7.48-7.51 (m, 3 H), 7.56-7.60 (m, 2 H), 7.69 (dd, 1 H, J = 4.4 Hz, 4.4 Hz), 7.80 (d, 2 H, J = 8.4 Hz), 7.89-7.94 (m, 2 H), 8.42 (d, 1 H, J = 8.4 Hz); ¹³C NMR (75 MHz, CDCl₃): δ = 24.2, 24.4, 27.5, 119.5, 123.0, 123.5, 125.5, 125.7, 125.8, 126.5, 126.7, 126.9, 127.0, 127.7, 128.0, 128.3, 129.4, 129.6, 131.9, 132.1, 132.9, 133.8, 134.3, 135.8, 136.5, 141.6, 143.7; HRMS (FAB): m/z calcd for C₂₇H₂₀ (M⁺): 344.1565, found: 344.1566.