Discussion
The major products X and Y formed in following reaction sequence are
- A.
- B.
- C.
- D.
Answer: C
X is 3-chloropyridine and Y is 4-aminopyridine, which is option (C).
Pyrrole with CHCl3 and KOH reacts with dichlorocarbene (the Ciamician-Dennstedt ring expansion). The carbene adds across the 2,3 C=C bond to give a dichlorocyclopropane that opens by loss of chloride and expands the ring, so the product is 3-chloropyridine, not 2-chloropyridine. With NaNH2 the aryl chloride loses HCl by elimination to give 3,4-pyridyne, and amide adds to the aryne mainly at C-4, giving 4-aminopyridine (the 3-amino isomer is the minor product).
Options (A) and (D) have 2-chloropyridine, which carbene ring expansion does not give. Option (B) has the right X but a 3-amino product, which is the minor isomer from the pyridyne.
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