Discussion
The major products Y and Z in the following reaction sequence are
- A.
- B.
- C.
- D.
Answer: A
The products are (A): Y is vinyl isocyanate and Z is benzyl N-vinylcarbamate.
Sodium azide replaces the chloride of acryloyl chloride to give acryloyl azide. On heating, the acyl azide undergoes the Curtius rearrangement: nitrogen gas is lost and the vinyl group migrates from carbon to nitrogen, giving vinyl isocyanate, CH2=CH-N=C=O (Y). Benzyl alcohol then adds across the C=N bond of the isocyanate to give the carbamate CH2=CH-NH-C(O)-OCH2Ph (Z).
(B) assumes azide adds to the C=C bond (conjugate addition) instead of replacing the chloride, and ignores the heating step. (C) is a 1,3-dipolar cycloaddition product, a triazoline. (D) keeps the acyl azide after heating, which is the condition that makes it rearrange, and then has benzyl alcohol add to the alkene instead of reacting with the isocyanate.
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