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DOI: 10.1055/s-2004-835631
Iridium Complex-Catalyzed Intramolecular Ene-Type Reaction of 1,6-Enynes Accelerated in Ionic Liquid
Publikationsverlauf
Publikationsdatum:
08. November 2004 (online)
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Abstract
Iridium complex catalyzes an intramolecular ene-type reaction of 1,6-enynes to give cyclic 1,4-dienes. The reaction proceeds more efficiently in an imidazolium salt than in toluene and the ionic liquid can be reused.
Key words
iridium - cycloisomerization - enynes - dienes - ionic liquid
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References
Using 1a- E as an enyne in toluene at 90 °C, no reaction proceeded by [RhCl(cod)]2 and many unidentified products were obtained by PtCl2.
12The higher reactivity of the E-isomer than the Z one is probably because the β-hydrogen is closer to the metal center in the metallacycle derived from the E-isomer. [4] However, the different selectivity of Ir- an Rh-catalyst could not yet be explained.
14Typical Experimental Procedure (Table 2, entry 3): Under an atmosphere of argon, [IrCl(cod)]2 (10.1 mg, 1.5 × 10-2 mmol, 5 mol%) and allyl propargyl ether 1a- E (54.7 mg, 0.300 mmol) were placed in a flask. After the addition of [BMIM]BF4 (0.5 mL), the mixture was stirred at 60 °C (bath temperature) for 1 h. The resulting mixture was extracted with Et2O, then the combined ether phase was evaporated to dryness, and the obtained crude products were purified by thin layer chromatography to give pure 2a (52.0 mg, 0.285 mmol, 95%).
15In [BMIM]BF4 at 60 °C, it took 3 h to consume 1a- Z and 2a was obtained in 43% yield.
18Under the same reaction conditions, crotylpropargylmalonate did not give an ene-type product.