Imine 13 was synthesized to further probe the conformational preferences of the presumed six-membered ring chelate. If steric crowding of one face of the chelate governed selectivity alone without any conformational considerations of the ). Reactions using TfOH, Cu(OTf)2 and BF3•OEt2 were all unselective (Table , entries 6, 8 and 9). The half-chair-like conformation invoked previously for imine 12 rationalizes the observed lower diastereomeric ratios for imine 13. Fürst-Plattner approach (avoidance of twist-boat products) of the nucleophile on lower energy conformer 18a is sterically unfavored as its trajectory is hindered by approach gauche to the methyl substituent (Figure ). On the other hand, Fürst-Plattner approach is sterically unincumbered in conformer 18b, though 18b is presumed to be higher in energy relative to that of conformer 17a due to bearing a pseudoaxial methyl group. As Fürst-Plattner rules are not reenforcing with the favored half-chair conformer of the chelate resulting from imine 13, the observed diastereomeric ratios are predictably lower.