Solution

ID: past-exam-of-the-chemistry-b-course-of-the-university-of-cambridge/2025/paper-1/b3/b/solution

Reduction makes stereogenic centres at C2 and C3 of the indan-1-one framework. The four products are the cis pair and , and the trans pair and . 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.
Figure 1.
Four hydrogenation stereoisomers of 2,3-diphenylindan-1-one and the two enantiomeric epoxides
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