Dithianes reduction with Raney nickel

Oxidative hydrolysis of an ethylene dithioketal. Cain and Welling report that the method of Corey and Erickson (4,216) for oxidative hydrolysis of 2-acyl-1,3-dithianes is also useful for unmasking of ethylene dithioketals. Thus treatment of the bisethylene dithioketal (1) with 4 eq. of NBS in 10% aqueous acetone at 0° for 20 min. selectively removes the less hindered ethylene dithioketal group at C to give (2) in 80% yield. Removal of the ethylene dithioketal group at C2 with Raney nickel requires reflux in ethanol and is accompanied by reduction of the carbonyl group. 

It is worth pointing out that a reductive treatment using LiAlH followed by a hydrogenolysis with Raney nickel affords the corresponding amines [13], while the treatment of the hydrazones with propan-l,3-dithiol in the presence of BFj.EtjO leads to the corresponding dithianes [14]. 

Raney nickel is a highly active, finely divided form of the metal prepared by reaction of a nickel/aluminum alloy with concentrated sodium hydroxide, which removes most of the aluminum as Na[Al(OH)4], Although active for a very wide range of reductions, it has been particularly widely used for the reduction of nitriles, and the desulfurization of thioacetals, thioethers, and dithianes (see Section 19.3.3) (Figure 23.22). The careful disposal of the catalyst after use is very important once it has dried out, the metal is highly pyrophoric. 

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