= Solution
Reduction makes <stereogenic centres> at C2 and C3 of the indan-1-one framework. The four products are the \b[cis pair $(2R,3S)$ and $(2S,3R)$], and the \b[trans pair $(2R,3R)$ and $(2S,3S)$]. Each pair consists of <enantiomers>; any cis member is diastereomeric to either trans member. There is no meso product because the carbonyl-containing and aromatic sides of the ring do not make C2 and C3 symmetry-equivalent.
For checking the <Cahn-Ingold-Prelog priority rules>, at C2 the order is carbonyl-side <carbon> $>$ phenyl $>$ C3 $>$ H. At C3 it is fused aromatic <carbon> $>$ phenyl $>$ C2 $>$ H. The fused aromatic path outranks the separate phenyl path because it reaches the carbonyl-containing part of the framework.
\Image[/past-exam-of-the-chemistry-b-course-of-the-university-of-cambridge/2025/paper-1-indanone-stereoisomers.png]
{title=Four hydrogenation stereoisomers of 2,3-diphenylindan-1-one and the two enantiomeric epoxides}
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