Q11 · CSIR NET Chemistry, June 2017
Paper: CSIR NET June 2017 · Subject: Organic Chemistry · Chapter: Reagents, Reaction Mechanisms & Named Reactions · Topic: Reagents, Reaction Mechanisms & Named Reactions – General · Marks: 2 · Difficulty: Medium
The correct combination of reagents A and B to effect the following transformations are 
$\xleftarrow{\ \mathrm{B}\ }$ 
$\xrightarrow{\ \mathrm{A}\ }$ 
$\xleftarrow{\ \mathrm{B}\ }$ $\xrightarrow{\ \mathrm{A}\ }$ (a)A = cat. $\mathrm{OsO_4}$, NMO; B = i) $\mathrm{I_2}$, $\mathrm{PhCO_2Ag}$ ii) aq. NaOH
(b)A = alkaline $\mathrm{KMnO_4}$; B = i) $\mathrm{I_2}$, $\mathrm{PhCO_2Ag}$, $\mathrm{H_2O}$ ii) aq. NaOH
(c)A = i) $\mathrm{I_2}$, $\mathrm{PhCO_2Ag}$ ii) aq. NaOH; B = cat $\mathrm{OsO_4}$, TMEDA, NMO
(d)A = m-CPBA, ii) aq. NaOH; B = alkaline $\mathrm{KMnO_4}$
Answer
Answer (as printed): B
Explanation
Transformation A gives the cis-exo-2,3-diol (both OH on the exo face). Cold alkaline KMnO₄ is a syn dihydroxylation and attacks norbornene from the less hindered exo face.
Transformation B gives the cis-endo diol. Under Woodward conditions (I₂, PhCO₂Ag with H₂O, then aq. NaOH), iodine adds to the exo face. Neighbouring-group participation by the benzoate through a dioxolanium ion places oxygen on the endo face, water traps it as the cis-hydroxy benzoate, and NaOH hydrolyses the ester to the cis-endo diol.
Why the others fail: (a) Prévost conditions without water give a trans diol; (c) puts a trans diol for A and OsO₄ gives the exo, not endo, diol for B; (d) m-CPBA then NaOH gives a trans diol for A. Answer: (b).
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