UPSC Combined Geo-Scientist, Mains · 2018 · Mains Paper III
Q6(f). Sequential electrocyclic reactions
Question
The depicted cis methyl/propenyl-substituted cyclobutene is heated to K, then irradiated to L. Identify the electrocyclic products.
Answer in brief
Thermal 4π opening gives an octa-2,4,6-triene; its cyclisable (2E,4Z,6E) branch K gives trans-5,6-dimethylcyclohexa-1,3-diene L photochemically.
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CoversSequential electrocyclic reactionsPericyclic stereochemistry
All parts of Question 6
- 6(a) Epoxidation and anti opening4 marks
- 6(b) Conjugate addition and dehydrogenation4 marks
- 6(c) Houben–Hoesch acylation4 marks
- 6(d) Pyrrole: formylation and expansion4 marks
- 6(e) Double Michael addition and Dieckmann closure4 marks
- 6(f) Sequential electrocyclic reactions4 marks
- 6(g) Benzyne trapped by isoindole4 marks
- 6(h) Pinacol rearrangement pathways4 marks
- 6(i) Rearranged alkylation and Birch reduction4 marks
- 6(j) Hydroboration–oxidation4 marks