Q30 · CSIR-NET Chemistry, December 2013
Paper: CSIR-NET December 2013 · Subject: Organic Chemistry · Chapter: Reagents, Reaction Mechanisms & Named Reactions · Topic: Reduction Reagents · Marks: 2 · Difficulty: Medium
The major product formed in the following reaction sequence is: 
(a)
(b)
(c)
(d)
Answer
Answer: A ✓ checked by 4AB · confidence high
Key A confirmed. The old explanation described two hydroxymethyl arms; option (a) carries one ring OH and one CH₂OH, and both C-1 and C-2 are lost.
Explanation
PhCHO/p-TsOH forms the 4,6-O-benzylidene acetal, leaving C-1, C-2 and C-3 free. NaIO₄ cleaves the C1–C2 and C2–C3 bonds: C-2 leaves as formic acid, C-1 as a formate ester on O-5 (lost on work-up), and C-3 becomes an aldehyde on C-4. NaBH₄ reduces that aldehyde to CH₂OH. The product is the 2-phenyl-1,3-dioxane (O-4, O-6) carrying a free OH at C-5 and a CH₂OH at C-4 — option (a).
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