What will be the major product of following sequence of reactions? $$\mathrm{n}-\mathrm{Bu}-\equiv \frac{\begin{array}{c}\text { (i) } \mathrm{n}-\mathrm{BuLi}, \\ \mathrm{n}-\mathrm{C}_{5} \mathrm{H}_{11} \mathrm{Cl}\end{array}}{\text { (ii) Lindlar cat, } \mathrm{H}_{2}}$$

JEE Main · 2022 · 27 Jun 2022 · Shift 2 · Hydrocarbons

What will be the major product of following sequence of reactions?

n - Bu - \equiv \frac{(i) n - BuLi , n - C _{5} H _{11} Cl}{(ii) Lindlar cat, H _{2}}

(A)(see structure)
(B)(see structure)
(C)(see structure)
✓ Correct
(D)(see structure)

Answer: (C)

Solution

The reaction sequence involves:
(i) n-BuLi deprotonates the terminal alkyne to form a nucleophilic acetylide anion (n-Bu-C≡C⁻Li⁺), which then undergoes nucleophilic substitution with n-C₅H₁₁Cl to form n-Bu-C≡C-C₅H₁₁.
(ii) Lindlar catalyst with H₂ performs syn-addition (cis-addition) to reduce the alkyne to a cis-alkene.

The major product is the cis-alkene with the butyl and pentyl groups on the same side of the double bond, which corresponds to option (C).

JEE Main · 2022 · 27 Jun 2022 · Shift 2 · Single correct option

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