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(b) Three sequential pericyclic reactions lead to formation of compound A. Section A Ph Ph (Answer any Two questions from this section) Meo Question 1 CO2Et Meo CO2Et (a) Consider the cycloaddition reaction shown below; H 6 n electrocylization Step 1 Phi Ph Ph Ph NH + Step 2 [1,5]-hydrogen shift CgH,NO2 + exo adduct CgH9NO2 endo adduct Ph maleimide cyclopentadiene CO2Et [3,3]-sigmatropic Meo. rearrangement (Claisen) Step 3 NH compound A [2 marks] [2 marks] [2 marks] [3 marks] Phí Ph i. How many a molecular orbitals does cyclopentadiene have? ii. Sketch the HOMO of cyclopentadiene in the ground state. iii. Provide the mechanism for this cycloaddition reaction. iv. Provide the structures for exo and endo adducts. v. Give the name of the orbital interactions that lower the energy of the transition state of endo adduct. vi. Which one of the two adducts (exo and endo) is kinetic? vii. What would happen to the rate of Diels-Alder reaction when cyclopentadiene is treated with ethene (CH2=CH2) instead of maleimide shown in the above example? i. Suggest detailed mechanisms for steps 1-3. ii. Draw the structure of compound A. [6 marks] [2 marks] [1 mark] [1 mark] (20 marks) [1 mark]

(b) Three sequential pericyclic reactions lead to formation of compound A. Section A Ph Ph (Answer any Two questions from this section) Meo Question 1 CO2Et Meo CO2Et (a) Consider the cycloaddition reaction shown below; H 6 n electrocylization Step 1 Phi Ph Ph Ph NH + Step 2 [1,5]-hydrogen shift CgH,NO2 + exo adduct CgH9NO2 endo adduct Ph maleimide cyclopentadiene CO2Et [3,3]-sigmatropic Meo. rearrangement (Claisen) Step 3 NH compound A [2 marks] [2 marks] [2 marks] [3 marks] Phí Ph i. How many a molecular orbitals does cyclopentadiene have? ii. Sketch the HOMO of cyclopentadiene in the ground state. iii. Provide the mechanism for this cycloaddition reaction. iv. Provide the structures for exo and endo adducts. v. Give the name of the orbital interactions that lower the energy of the transition state of endo adduct. vi. Which one of the two adducts (exo and endo) is kinetic? vii. What would happen to the rate of Diels-Alder reaction when cyclopentadiene is treated with ethene (CH2=CH2) instead of maleimide shown in the above example? i. Suggest detailed mechanisms for steps 1-3. ii. Draw the structure of compound A. [6 marks] [2 marks] [1 mark] [1 mark] (20 marks) [1 mark]