Q9(d)(i). Birch reduction with ring closure: a spiro acid
Formulate the products and mechanisms of the following reactions: (i) 4-(4-bromobutyl)benzoic acid, Li/liq. NH₃ → ? [structure given in the paper]
Answer in brief
Spiro[4.5]deca-6,9-diene-8-carboxylic acid: Birch reduction of the ring, in which the para carbanion closes a five-membered ring on its own CH₂Br group.
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CoversBirch reductiondissolving metal reductionradical anionintramolecular alkylationspiro compound
All parts of Question 9
- 9(a) Structure from UV, IR, NMR and mass data: C₇H₈BrN10 marks
- 9(b) Dieckmann condensation, then hydrolysis and decarboxylation5 marks
- 9(c) Beer’s law for camphor; λmax of the methyl halides5 marks
- 9(d)(i) Birch reduction with ring closure: a spiro acid5 marks
- 9(d)(ii) Robinson annulation to a spiro enone5 marks