Problem Set 7 – Reactions of aldehydes and ketones

1. Outline a synthesis of the following compounds starting from either benzene or toluene:

1. n-butylbenzene

2. 1-phenyl-2-propanone

2. Outline a synthesis of 3-hexene from propene.

3. Bombykol, the sex pheromone of the silkworm moth, has been prepared in the following way:

1-pentyne + n-C₄H₉MgBr ® A (C₅H₇MgBr)

A + HCHO; then H⁺ ® B (C₆H₁₀O)

B + PBr₃ ® C (C₆H₉Br)

C + Ph₃P, base ® D (C₂₄H₂₃P)

D + OHCCH₂(CH₂)₇CO₂C₂H₅ ® E (C₁₈H₃₀O₂)

E + H₂/Pd ® F (C₁₈H₃₂O₂)

F + LiAlH₄ ® bombykol (C₁₆H₃₀O)

Give the structures of compounds A to F and that of bombykol.

4. Propose a mechanism for the following reaction:

5. Compound “A”, C₆H₁₂O₂, was found to be optically active. Reaction with Tollens reagent gave “B”, C₆H₁₂O₃, an optically active carboxylic acid. Oxidation of “A” by pyridinium chlorochromate in dichloromethane gave an optically inactive compound which reacted with Zn(Hg)/HCl to give 3-methylpentane. Vigorous oxidation of “A” yielded “C”, C₆H₁₀O₄, an optically inactive dicarboxylic acid. Give the structures of compounds “A”, “B”, and “C”.