Zinc-copper couple reductive amination

Under conventional dechlorination conditions (20 equiv of zinc dust, acetic acid, 25°C or 50°C) the reduction of 4,4-dichlorocyclobutenones affords complex mixtures of products which include the desired cyclobutenones as well as significant amounts of partially reduced byproducts. He have found that the desired transformation can be accomplished cleanly provided that the reduction is carried out at room temperature in alcoholic solvents (preferably ethanol) in the presence of 5 equiv each of acetic acid and a tertiary amine (preferably tetramethylethylenediamine). Zinc dust has proven to be somewhat superior to zinc-copper couple for this reduction. The desired cyclobutenones are obtained in somewhat higher yield using this procedure as compared to the related conditions reported by Dreiding [Zn(Cu), 4 1 AcOH-pyridine, 50-60 C] for the same transformation. ... 

The chloro nitroso adducts of the ( -protected glycals were converted, via the intermediate oximes, to 2-amino-2-deoxy sugars48,50,53,59 the overall oxyamination of glycals is hence accomplished. Amines of the opposite configuration are prepared depending on the method of reduction. The chloro nitroso adducts can be directly treated with zinc-copper couple in acetic acid, or can be first converted to fully acetylated oximes which are then catalytically hydrogenated. 

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