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In the following sequence of reactions, identify the structures of intermediates Y, Z, W, and M: Y --(NaBH4)--> Z --(conc. HBr)--> W Y --(N2H4 / KOH, heat)--> M M --(NBS, heat/light)--> W W --(1) Mg/ether, (2) CO2, (3) H3O+)--> Ph-CH(COOH)-CH2-CH3 Which of the following statements about the intermediates is correct?

1. Z is (plus/minus) Ph-CH(OH)-CH2-CH3
2. Y is Ph-CH(OH)-CH3
3. W is a compound in which bromine is attached directly to the aromatic ring
4. M is Ph-CO-CH2-CH3

Correct answer: Z is (plus/minus) Ph-CH(OH)-CH2-CH3

Solution

Working backwards: W = Ph-CH(Br)-CH2-CH3 (secondary benzylic bromide). Z is obtained by NaBH4 reduction of ketone Y, giving the racemic secondary alcohol Ph-CH(OH)-CH2-CH3. Therefore Z = (+-) Ph-CH(OH)-CH2-CH3, making statement 1 correct. Y is Ph-CO-CH2-CH3 (propiophenone), not Ph-CH(OH)-CH3, so statement 2 is false.

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