Addition of Dichloroketene to Styrene; Cyclobutanones

Colin Morton ([email protected]),
A contribution from the Scott Group, Warwick

Chemicals Used
Styrene (Aldrich, distilled), Zinc dust (Aldrich), Copper Sulfate hydrated (Aldrich), Diethyl Ether (Aldrich, dried over Na/K alloy), Trichloroacetyl Chloride (Aldrich), Phosphorous oxychloride (Aldrich, under Argon)

Procedure
Activation of Zinc: Zinc (20 g) was stirred in 20% HCl for 15 mins. After filtration it was washed with water (50 ml) and acetone (50 ml) and dried in vacuo. Zinc/Copper Couple: A stirred suspension of activated zinc (10 g) in water (40 ml) was degassed by bubbling N₂ through it for 1 hr. To this was then added CuSO₄.5H₂O (1.18 g). The resulting black suspension was stirred for an extra 3 hrs with bubbling N₂. The Zn-Cu couple was collected on a sintered funnel and washed with water (100 ml) and acetone (100 ml) and dried in vacuo. The couple was stored in a dessicator over silica gel. 2,2-dichloro-3-phenylcyclobutanone: To a dry 2 necked 50 ml RBF under Argon was added styrene (1.1 ml, 9.6 mmol), Zn-Cu Couple (0.69 g, 10.5 mmol) and anhydrous Et₂O (20 ml). To this was added a solution of Cl₃CCOCl (1.1 ml, 10.0 mmol) and POCl₃ (0.92 ml, 10.0 mmol) in Et₂O (20 ml) over 1 hr. The resulting mixture was then refluxed for 4 hrs. The suspension was then filtered through a pad of celite which was subsequently washed with bench Et₂O (50 ml). The organic solution was then subsequently washed with water (100 ml), saturated NaHCO₃ (50 ml), brine (50 ml) and water (50 ml). Separation from the aqueous phase and removal of all volatile organics gave a yellow oil that was purified by trap-to-trap distillation (90^oC, 10^-3)to give a white crystalline solid. Yield 1.6 g, 77%. 3-phenylcyclobutanone: The halogenated product above was heated in glacial acetic acid (30 ml) for 2 hrs. Standard aqueous work-up and purification by trap-to-trap distillation (85^oC, 10^-3) gave a clear colourless oil.

Author's Comments
It is worth activating the zinc before making the Zn-Cu couple-it really makes a difference.

Data
3-phenylcyclobutanone (CDCl₃) 7.2-7.5 (m, 5H), 3.2-3.7 (m, 5H).

Lead Reference
J.Org.Chem., 43,1978,2879 J.Org.Chem., 48,1983,3382

Other References

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