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Ketone reduction to methylene; Dibenzosubarane from dibenzosubarone

SyntheticPage 928
Submitted Jul 01, 2020, published Jul 02, 2020
Ramesha Ramakrishna (
A contribution from ramesha

			Reaction Scheme: Ketone reduction to methylene

Chemicals Used

  1. Dibenzosuberone, commercial, Min 95%
  2. Ni-Al alloy (50:50), commercial.
  3. Toluene, commercial, 99%
  4. Sodium Hydroxide - commercial, min 99%


To a stirred solution of dibenzosuberone (50 g, 0.24 mol) in 0.025 M aqueous sodium hydroxide (500 mL, 0.5 g NaOH in 500 mL water) under nitrogen atmosphere, was added nickel-aluminium alloy (50 g) in small portions at 50-60°C over a period of 4 hours. After complete addition of Ni-Al alloy, the reaction mixture was heated and stirred at 90-98 °C until the completion of reaction (10h, monitored by TLC, 1:9, Ethyl acetate: Hexane). The reaction was cooled to room temperature under nitrogen atmosphere and toluene (100 mL) added and stirred for 5 min. On stopping the stirring, Ra-Ni settles in the bottom. Toluene layer can be decanted. This procedure can be repeated again with toluene (100 mL) (100 mL x2, Note: This process gives highly active pyrophoric Raney Nickel which can be disposed of in water.). The organic layer was dried over anhydrous sodium sulphate and filtered, solvent was removed completely under vacuum to get pale yellow dibenzosubarane. The product thus obtained is practically pure by NMR. (Yield: 42.5-43.5 g, Yield: 95%).

Author's Comments

1. Ni-Aluminium (50:50) alloy should not be added all at once. This might lead to runaway reaction.

2. Reaction should be carried under nitrogen atmosphere. Ra-Ni produced as by product is pyrophoric. Ra-Ni should be kept under water.




1H NMR (400 MHz, CDCl3): δ 7.18-7.00 (m, 8H), 4.04 (s, 2H), 3.4(s, 4H);

13C NMR (100 MHz, CDCl3): δ 33.1, 41.5, 126.6, 127.2, 129.6, 130.1, 139.5, 139.8.


Lead Reference

Lead reference:

1. Mitchell, R. H.; Lai, Y.H. Tetrahedron Lett. 1980, 21, 2637.

2. Keefer, L. K.; Lunn, G. Chem. Rev. 1989, 89, 459.



Other References


Supplementary Information

1H and 13C NMR (SYnthesis of Dibenzosubarane NMR.docx)

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Get structure file (.cdx, .sk2, .mol)

Keywords: Dibenzosubarane, Dibenzosuberone, ketones, Ni-Al alloy, reduction

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