Montmorillonite K10-Catalyzed Aza Diels-Alder Reaction of Danishefsky’s Diene with Aldimines, Generated in situ from Aliphatic Aldehydes and Amine, in Aqueous Media

Abstract

The montmorillonite K10-catalyzed aza Diels-Alder reaction of Danishefsky’s diene with aldimines, generated in situ from aliphatic aldehydes and p-anisidine, proceeded smoothly in H₂O or in aqueous CH₃CN to afford 2-substituted 2,3-dihydro-4-pyridones in excellent yields.

Key words

Diels-Alder reactions - Danishefsky’s dienes - montmorillonite - water - Schiff bases

References

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12

Although we have reported the three-component aza Diels-Alder reaction of aldimine, derived from aliphatic aldehydes, with Danishefsky’s diene, [11] yields of the adducts are not excellent.

17

General experimental procedure for conditions B (entry 5 of Table [3] ): To a solution of CH₃CN (0.9 mL) and H₂O (0.1 mL) were added p-anisidine (17.7 mg, 0.144 mmol), butanal (14.0 µL, 0.155 mmol) at -10 °C. After being stirred at the temperature for 10 min, Danishefsky’s diene (82.0 µL, 0.429 mmol) and montmorillonite K10 (75.4 mg) were added successively. After being stirred at the temperature another 1.5 h, catalysts were removed by filtration. The montmorillonite K10 was washed with a mixture of CH₂Cl₂-MeOH (4:1). The filtrate was dried over anhydrous Na₂SO₄, and concentrated to dryness. Purification of the crude mixture by preparative TLC (SiO₂, hexane-ethyl acetate = 10: 1, v/v, containing 2% Et₃N) gave propyl-substituted 2,3-dihydro-4-pyridone (34.6 mg, 0.141 mmol) in 89% yield.

18

The reaction in water was run at 0 °C (bath temperature), while those in CH₃CN-H₂O and CH₃CN were carried out at -10 °C.