Synthesis of 1,3-Disubstituted Pyrroles

Russian workers have recently described an interesting synthesis of 1,3-disubstituted pyrroles which consists of the following 3-step procedure, illustrated for the preparation of 1-benzyl-3 -ethylpyrrole (from which 3-ethylpyrrole is easily available by Na/NH3 reductive removal of the benzyl group)  

Elucidate the reaction scheme, identify A and suggest a mechanism for the conversion of A into l-benzyl-3-ethylpyrrole. 

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