Iridium Complex-Catalyzed Pauson-Khand-Type Reaction of Allenynes

Abstract

Vaska’s complex [IrCl(CO)(PPh₃)₂] efficiently catalyzes the intramolecular carbonylative [2+2+1] cycloaddition of allenynes. A dimethyl substituent on the allene terminus and a low partial pressure of carbon monoxide realize the selective engagement of the internal π-bond of allene.

Key words

alkynes - allenes - carbonylations - iridium - Pauson-Khand reaction

References

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13

A typical experimental procedure is as follows (Table [2] , entry 1): Under an atmosphere of CO (0.2 atm) and Ar (0.8 atm), IrCl(CO)(PPh₃)₂ (8.2 mg, 1.05 × 10^-2 mmol, 5 mol%) was placed in a flask. A degassed xylene solution (5 mL) of allenyne 1a (44.6 mg, 0.210 mmol) was added, and the mixture was the stirred at 120 °C (bath temperature) for 3 h. The solvent was removed under a reduced pressure, and the resulting crude products were purified by thin layer chrom-atography to give pure 2a (40.3 mg, 0.161 mmol, 77%). 4-Methylpenta-2,3-dienyl 3-phenyl-2-propynyl ether (1a). Yellow oil; IR (neat) 2826, 2364, 1448, 1122 cm^-1; ¹H NMR δ = 1.72 (d, J = 3.0 Hz, 6 H), 4.10 (d, J = 6.6 Hz, 2 H), 4.38 (s, 2 H), 5.04-5.13 (tq, J = 3.0 Hz, 6.6 Hz, 1 H), 7.28-7.32 (m, 3 H), 7.42-7.45 (m, 2 H); ¹³C NMR δ = 20.3, 57.2, 68.5, 85.1, 85.6, 86.0, 96.1, 122.7, 128.2, 128.3, 131.7, 203.4; HRMS found m/z 212.1209, calcd for C₁₅H₁₆O: 212.1201. 4-Isopropylidene-2-phenyl-7-oxabicyclo[3.3.0]-oct-1-en-3-one (2a). White solid; mp 109-110 °C (hexane); IR (neat) 1686, 1632, 1023 cm^-1; ¹H NMR δ = 1.94 (s, 3 H), 2.37 (s, 3 H), 3.20 (dd, J = 7.9 Hz, 11.1 Hz, 1H), 3.79-3.85 (m, 1 H), 4.44 (dd, J = 7.9 Hz, 7.9 Hz, 1 H), 4.50 (d, J = 15.4 Hz, 1 H), 4.91 (dd, J = 1.2 Hz, 15.4 Hz, 1 H), 7.25-7.43 (m, 3 H), 7.56-7.58 (m, 2 H); ¹³C NMR δ = 19.8, 25.2, 47.9, 65.7, 69.7, 128.1, 128.3, 128.4, 130.9, 131.4, 137.5, 148.2, 168.2, 194.6; HRMS found m/z 240.1150, calcd for C₁₆H₁₆O₂: 240.1150.