The aza-Cope Mannich reaction sequence has been shown to be an effective method for generating substituted pyrrolidines as part of the overall synthesis of natural and unnatural polyhydroxylated pyrrolizidine alkaloids. In this work we use density functional methods to determine the activation barriers for a series of C-C bond rotations that interconvert four iminium cation stereoisomers that are precursors to the aza-Cope - Mannich reaction. These activation barriers are compared to those for the rate determining step of the reaction and are found to be much smaller. This would indicate that loss of stereospecificity does not occur prior to the tandem reaction. The effect of the substituent size and electron withdrawing ability on activation barriers is also investigated.

Computational analysis of activation barriers to C-C bond rotations for an iminium cation

244th National Meeting (2012)

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