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SolutionsFunctional group interconversion

Exercise 1

Give an FGI that allows a simple disconnection in: a) 2-phenylethanol; b) 4-methylaniline; c) (E)-but-2-en-1-ol obtained from an aldehyde.

a) None is needed: the primary alcohol disconnects into PhMgBr + ethylene oxide; alternatively by FGI, PhCH2CO2H and reduction with LiAlH4. b) NH2 ⇒ NO2: 4-nitrotoluene, by nitration of toluene (and separation of the ortho isomer), then reduction. c) CH2OH ⇒ CHO: (E)-but-2-enal (crotonaldehyde), selectively 1,2-reduced with NaBH4 and CeCl3 (Luche reduction); the aldehyde comes from the aldol condensation of acetaldehyde.

Exercise 2

How would you prepare N-ethylaniline without forming N,N-diethylaniline? Propose two routes based on FGIs.

1) Reductive amination: aniline + acetaldehyde and NaBH3CN (or NaBH(OAc)3); the imine is reduced to the secondary amine. 2) FGI amine ⇒ amide: acetylation of aniline with acetic anhydride to acetanilide and reduction with LiAlH4, which turns C=O into CH2. In both cases only one N–C bond is formed.