In the following reaction sequence, the correct structure(s) of X is (are)
(A)(see structure)
(B)(see structure)✓ Correct
(C)(see structure)
(D)(see structure)
Answer: (B)
Solution
The reaction sequence shows:
Hydroboration-oxidation of an alkene produces an anti-Markovnikov alcohol.
Oxidation with PCC converts the alcohol to a ketone.
Reduction with NaBH4 converts the ketone back to an alcohol.
For the product to be a trans-1,2-disubstituted cyclopentane, X must be the cis-isomer of 2-methylcyclopentanol. The hydroboration-oxidation is syn-addition, and the stereochemistry must be consistent with the final product.
Analyzing the stereochemistry through the reaction sequence, only option (B) gives the correct final product.
Correct answer: (B).
JEE Advanced · 2018 · 20 May 2018 · Paper 1 · One or more correct options
