1. Give a step-by-step mechanism (showing appropriate curly arrows) for the formation of an imminium ion from the components shown below. How does the imminium ion compare to the precursor a,13-unsaturated aldehyde in terms of reactivity (specify what the other reaction partner might be when describing the reactivity differences)?
2. Draw the enantiomer of proline which would give rise to the absolute stereochemistry shown in the reaction below. Justify your answer by showing the key intermediate in the catalytic cycle and show a stereochemical model for the C-N bond formation.
3. Predict the product of the reaction shown below. Is the mode of catalysis is `enamine' or 'imminiumi. Draw a proposed catalytic cycle for the transformation. How does the catalyst activate the substrate?
4. Predict the precursor in the reaction shown below. Is the mode of catalysis 'enamine' or 'imminium'? Draw a proposed catalytic cycle for the transformation. How does the catalyst activate the substrate?
