= Solution
The oxime is reduced at its C=N bond rather than cleaving N–O: <hydride> addition to the <imine> <carbon> followed by <protonation> gives an \b[N-substituted hydroxylamine]. In a chair-like model of the cis-fused ring system, the fused framework and methyl group make the two faces inequivalent. The favoured <hydride> trajectory accesses the face that places the newly installed C–H bond behind the original drawing and the retained \b[C–NHOH bond in front], giving D. It avoids the more congested trajectory into the folded bicyclic framework; a flat hexagon comparison alone misses this facial distinction.
The existing methyl and junction centres are retained. The selectivity is therefore \b[diastereoselective substrate control], not enantioselectivity from <sodium cyanoborohydride>, which is achiral. For a racemic starting bicycle the same relative stereochemical preference gives a racemic pair of D <enantiomers>.
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