Reduction of oximes with sodium borohydride - copper ( II ) su lfate in methanol

Reduction of oxi me fu nctionality to amine is an important synthetic transformation . As ox imes are stable derivatives of carbonyl compounds, subsequent reduction to amines is an attractive two-step procedure for reductive ami nation . Red uction of oximes to amines can be performed by hydride reducing agents or by catalytic hydrogenation.' Among hydride reducing agents, lithium aluminium hydride is commonly employed for thi s purpose. However, this reagent is non-se lective and difficult to handle. On the other hand, sodium borohydride is a mild reducing agent effective on ly for the reduction of aldehydes, ketones and acy l halides . Its reducing power can be enhanced as well as altered in the presence of transition metal sa lts such as nickel (II) chloride, cobalt (II) chloride, titanium (IV) chloride etc. Complex metal borides in conjugation with sodium borohydride were proposed as the actual reducing reagents, mimicking catalytic hydrogenation . Prev iously, we have fou nd that sodium borohydride-copper sul fate is an efficient and convenient reagent for the reducti on of azides to primary amines. 3 In conti nuation, we now report our studies on the reduction of oximes with this reagent. Prev iously, Ipakstschi 4 reported the reducti on of some ketoximes to primary ami nes w ith sodium borohydride and nickel (II ) chloride. We now found that reduction of oximes with sodium borohydride and copper (11 ) su lfate yields primary as well as secondary amines in varying ratios depending on the nature of the oxime (Scheme I). Results obtained in thi s study are gathered in the Table I. Reduction of benzaldehyde ox ime la , an aromat ic aldoxime, was studied initi ally as a representative example. Addition of one equi valent of sod ium boroMeOH,. reflux 2a-g 3a-g