Q6(g). [1,5]-Carbon shift and Cope rearrangement
Complete the following reactions and indicate how they are formed: (i) a cis-dimethyl spiro cyclopentadiene, Δ → ? (ii) cis-1,2-divinylcyclopropane, Δ → ? [structures given in the paper]
Answer in brief
(i) cis-4,7-Dimethyl-4,5,6,7-tetrahydro-3aH-indene by a thermal [1,5]-carbon shift with retention, followed by fast [1,5]-H shifts. (ii) Cyclohepta-1,4-diene by a Cope ([3,3]) rearrangement.
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Coverssigmatropic rearrangement[1,5]-shiftCope rearrangementdivinylcyclopropanepericyclic reaction
All parts of Question 6
- 6(a) Curtius rearrangement; the isocyanate closes to a cyclic urea4 marks
- 6(b) HBr and a conjugated diene: 1,2- and 1,4-addition4 marks
- 6(c) Phenylglycine and mandelic acid from benzaldehyde4 marks
- 6(d) Coumarin and 3-acetylcoumarin from salicylaldehyde4 marks
- 6(e) Intramolecular oxymercuration–demercuration: a cyclic ether4 marks
- 6(f) trans- and cis-Cyclohexane-1,2-diol from cyclohexanone4 marks
- 6(g) [1,5]-Carbon shift and Cope rearrangement4 marks
- 6(h) Four C₁₀H₁₄ isomers: the one marked by a McLafferty peak4 marks
- 6(i) C₃H₇NO with two N–methyl singlets: N,N-dimethylformamide4 marks
- 6(j) ν(C=C) of methylidenecycloalkanes and ring size4 marks