 Solution

ID: past-exam-of-the-chemistry-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2021/paper-1/3/c/solution

Let

Ar = p - MeO C_{6} H_{4}

. One standard route is:

ArBr M g dry ether or THF ArMgBr C H_{3} C H O then aqueous workup ArCH (OH) C H_{3} catalytic p -TsOH Δ ArCH = C H_{2} m CPB A ArCH - C H_{2}

where the last two carbons are joined through oxygen to form the epoxide shown in the product drawing.

Use rigorously dry conditions for Grignard formation/addition; quench only after the aldehyde addition. Dehydration gives the styrene, and peracid oxidation transfers oxygen across its double bond. The methoxy substituent is compatible with this sequence. No asymmetric reagent is specified, so the target epoxide is racemic.

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