Q2(d). Thermal oxygen–sulfur interchange
Identify A, B and C from the R-substituted pyran-2-thione on successive heating, showing electron flow. [structure of the pyran-2-thione given in the paper]
Model answer
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Coverspyran-2-thioneelectrocyclic ring openingsigmatropic hydrogen shiftpericyclic reactionsoxygen–sulfur interchange
All parts of Question 2
- 2(a) Neighbouring acetate participation10 marks
- 2(b) Dehydration with carbocation rearrangement10 marks
- 2(c) Favorskii reactions of two alpha-haloketones10 marks
- 2(d) Thermal oxygen–sulfur interchange10 marks