Q7(b). Oxepin: 6π electrocyclic ring closure, then Diels–Alder addition
Explain the type of ring closure and the major product A formed in the following reaction: oxepin + MeOOC–C≡C–COOMe, Δ → A. [structures given in the paper]
Answer in brief
Thermal 6π electrocyclic, disrotatory ring closure: oxepin closes to benzene oxide. A is the Diels–Alder adduct of benzene oxide with the diester: dimethyl 3-oxatricyclo[3.2.2.0²,⁴]nona-6,8-diene-6,7-dicarboxylate.
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Coverselectrocyclic reactionoxepinbenzene oxideDiels–Alder reactionDMADvalence tautomerism
All parts of Question 7
- 7(a)(i) Schmidt reaction of a cyclohexanone with an alkyl azide5 marks
- 7(a)(ii) Robinson annulation of 2-methylcyclohexane-1,3-dione5 marks
- 7(b) Oxepin: 6π electrocyclic ring closure, then Diels–Alder addition5 marks
- 7(c) Chloromethylation, then Sommelet–Hauser rearrangement5 marks
- 7(d)(i) Iodolactonisation of a cyclopentenylacetic acid5 marks
- 7(d)(ii) Epoxidation, then acid-catalysed ring expansion to a ketone5 marks