The aza-Prins reaction is a facile method for preparing functionalized piperidines.  Typically the reaction proceeds by condensation of an electron deficient homo-allylic amine with an aldehyde.  The resulting iminium cation readily undergoes cyclization.  However, few examples of aza-Prins reactions of unactivated imines have been described.  To this end, we have developed a microwave-assisted aza-Prins reaction of unactivated imines using mild Lewis acid mediation.  This reaction produces 2,4-disubstituted piperidines in good to excellent diastereoselectivities.  However, in the course of optimizing the aza-Prins reaction, we found evidence of a competing aza-Cope rearrangement.   Attempts to selectively trap the aza-Cope products as well as efforts to suppress this reaction in favor of piperidine formation will be described.

Piperidines via a microwave-assisted aza-Prins reaction

253rd National Meeting (2017)

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