Discussion
The major product formed in the following reaction is
- A.
- B.
- C.
- D.
Answer: C
The major product is (C), α-methylene-γ-butyrolactone.
Silver carbonate on Celite (Fetizon's reagent) is a mild oxidant that converts 1,4-diols to γ-lactones. One alcohol is oxidised to the aldehyde, which cyclises with the other OH to a five-membered lactol, and the lactol is oxidised further to the lactone. The reagent oxidises the more reactive allylic CH2OH first, so the carbonyl carbon of the lactone is the one next to the C=CH2 group. That puts the exocyclic methylene α to the carbonyl, as in (C).
(A), the β-methylene lactone, would come from oxidising the other, non-allylic alcohol first. (B) and (D) stop at aldehyde stages; under these conditions the 1,4-hydroxy aldehyde closes to the lactol and goes on to the lactone.
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