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This shows the mechanism for pyrrole synthesis based on recent DFT study. Instead of the formation and cyclisation of a enamine intermediate, a hemiaminal intermediate in formed, followed by the consecutive dehydrations of the two hydroxyl groups. The dehydration steps may look familiar: it is just the formation of an enamineA more traditional approach to the mechanism, which appears in some text books and taught courses, can be found here.
This mechanism was based on the paper: B. Mothana, R. J. Boyd, J. Mol. Struct.: THEOCHEM, 2007, 811, 97-107