The major product formed in the following reaction is · ABC26OR0605
Subject: Organic Chemistry · Chapter: Reagents, Reaction Mechanisms & Named Reactions · Topic: Reagents, Reaction Mechanisms & Named Reactions – General · Exam: GATE 2000-2022 · Marks: 2 · Difficulty: Medium
The major product formed in the following reaction is 
(a)
(b)
(c)
(d)
Answer
Answer: B ✓ checked by 4AB · confidence high
The source book printed no answer; this one was worked out and checked — see the explanation.
Explanation
B₂H₆ reduces the free –COOH quickly (through an acyloxyborane) and leaves the –COOCH₃ untouched, giving HOCH₂CH₂–CH(iPr)–CH₂COOCH₃. Acid then drives intramolecular transesterification: the primary OH attacks the ester, MeOH is lost, and the six-membered δ-lactone 4-isopropyltetrahydropyran-2-one closes. The stereocentre is not touched. In the substrate it is R (iPr > CH₂CO₂Me > CH₂CO₂H, H back). In the lactone the same spatial arrangement is again R (iPr > CH₂C(=O)O > CH₂CH₂O), which is the drawing in (b). (a) is its enantiomer; the ether (c) and the enol ether (d) do not form. Answer: (b).
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