[7440-66-6]  · Zn  · Zinc-Dimethylformamide  · (MW 65.39) (DMF)

[68-12-2]  · C3H7NO  · Zinc-Dimethylformamide  · (MW 73.11)

(reducing agent for halides,3 azides,10 and aldehydes11)

Physical Data: zinc: mp 419.5 °C; d 7.140 g cm-3; DMF: bp 153 °C; d 0.944 g cm-3.

Solubility: sol DMF, THF, Et2O, toluene, alcohol.

Preparative Methods: see text.

Handling, Storage, and Precautions: see Zinc and N,N-Dimethylformamide.

Reduction of Halides.

The first use of a mixture of zinc and DMF as a dehalogenating reagent was employed by Alder and Fremery in 1961.1 In a study of formation of ortho biradicals, they employed Zn/DMF to reduce a,a-dibromoxylene (eq 1) which generated unstable 5,6-dimethylene-1,3-cyclohexadiene. This diene undergoes a Diels-Alder reaction with dienophiles like Acrylonitrile, Acrolein, and Ethyl Acrylate in high yield. A similar reaction has also been employed in the dimethylenecyclooctatriene system.2

A systematic study of Zn/DMF as a dehalogenating reagent was investigated by Mehta and Kapoor.3 It was found that ordinary zinc powder reacts with a variety of alkyl halides in DMF to furnish the corresponding organozinc compounds. Aqueous decomposition of these solutions gave the expected hydrocarbons in good yield. The procedure is a satisfactory alternative for dehalogenation when the commonly employed hydride complexes4 or metal amines5 cannot be used. For example, 8,15-dibromolongibornan-9-one was reduced to longibornan-9-one in 82% yield using Zn/DMF (eq 2).

In a subsequent study, reaction of dibromocyclopropane with Zn/DMF gave monobromocyclopropane (eq 3), allene (eq 4), or a mixture of products (eq 5), depending on the ring system of the substrate.6 Thus no generalization could be made. The yields of some of the products formed from gem-dibromocyclopropanes were comparable to those obtained by other methods.

Reduction of Azides.

Carbohydrate azides are valuable intermediates for the synthesis of amino sugars. This transformation is commonly brought about by catalytic reduction7 or by treatment with Lithium Aluminum Hydride8 or Sodium Borohydride.9 Ohrui and Emoto discovered that Zn/aq DMF is an excellent reagent to reduce an azide group to the corresponding amine group (eq 6).10 This reaction was complete in 45 min whereas the corresponding sodium borohydride reduction required 20-30 h.

Reduction of Aldehydes to Alcohols.

A mixture of Zn and Antimony(III) Chloride in aqueous DMF reduces aldehydes to the corresponding alcohols in excellent yield.11 A variety of aliphatic (eq 7), aromatic (eq 8), and a,b-unsaturated (eq 9) aldehydes were reduced to alcohols under relatively mild conditions.

1. Alder, K.; Fremery, M. T 1961, 14, 190.
2. Elix, J. A.; Sargent, M. V.; Sondheimer, F. JACS 1970, 92, 962.
3. Mehta, G.; Kapoor, S. K. JOM 1974, C33.
4. Gaylord, N. G. Reduction with Complex Metal Hydrides; Wiley: New York, 1956.
5. House, H. O. Modern Synthetic Reactions; Benjamin: New York, 1965.
6. Mehta, G.; Kapoor, S. JOM 1974, 213.
7. Dick, A. J.; Jones, J. K. N. CJC 1965, 43, 977.
8. Cléophax, J.; Géro, S. D.; Hildesheim, J. CC 1968, 94.
9. (a) Boyer, J. H.; Ellzey, S. E. JOC 1958, 23, 127. (b) Ali, Y.; Richardson, A. C. Carbohydr. Res. 1967, 5, 441.
10. Ohrui, H.; Emoto, S. Carbohydr. Res. 1969, 10, 221.
11. Wang, W. B.; Shi, L. L.; Huang, Y. Z. TL 1990, 31, 1185.

Hemantkumar H. Patel

Abbott Laboratories, North Chicago, IL, USA

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