Pyrroline Mannich reaction

The imine and iminium functional groupings are, of course, the nitrogen equivalents of carbonyl and O-protonated carbonyl groups, and their reactivity is analogous. The Mannich reaction of pyrrole produces dialkylaminomethyl derivatives, the iminium electrophile being generated in situ from formaldehyde, dialkylamine and acetic acid. There are only a few examples of the reactions of imines themselves with pyrroles the condensation of 1-pyrroline with pyrrole as reactant and solvent is one such example. N-Tosyl-imines react with pyrrole with Cu(OTf>2 as catalyst. ... 

The trimer of 1-piperidine, best prepared by dehydrochlorination of N-chloropiperidine, has been known for some time. 1-Pyrroline also appears to exist largely as the trimer. Both undergo Mannich reactions with electron-rich heterocycles. Indole reacts with 1-piperidine in a citrate buffer to afford 3-(2-piperidyl)indole in 40-55% yield (equation 45). ° The iV-methylpiperidyl analog has also been... 

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