Major products P and Q, in the given reaction sequence, are: P Q · ABC26OR0615
Subject: Organic Chemistry · Chapter: Reagents, Reaction Mechanisms & Named Reactions · Topic: Reagents, Reaction Mechanisms & Named Reactions – General · Exam: GATE 2000-2022 · Marks: 2 · Difficulty: Medium
Major products P and Q, in the given reaction sequence, are: 
P 
Q
P Q(a)and
(b)and
(c)and
(d)and
Answer
Answer: A ✓ checked by 4AB · confidence low
The source book printed no answer; this one was worked out and checked — see the explanation.
Explanation
9-BBN (1 eq) hydroborates one C=C of the 5-substituted cyclopentadiene from the face anti to CH₂CO₂Et, with boron going to the carbon next to the substituted sp³ carbon. H₂O₂/NaOH then replaces B by OH with retention, so P = trans-2-(ethoxycarbonylmethyl)cyclopent-3-en-1-ol. MsCl/Et₃N turns the OH into OMs. NaOH saponifies the ester, and the carboxylate displaces the mesylate intramolecularly by SN2 with inversion, so the γ-lactone is cis-fused. H₂/(Ph₃P)₃RhCl finally reduces the ring C=C. Q = cis-fused bicyclic γ-lactone. Answer: (a).
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