Influence of Remote Stereocenters

The C4 stereocenter dominates the stereochemical outcome of the Ireland-Claisen rearrangements in appropriately substituted allyl silyl ketene acetals. For substrates lacking a C4 stereocenter, other more remote stereocenters may play a significant role in the stereochemical outcome. There are comparatively few cases of remote stereocontrol, so most examples will be described in this section. The stereocenters will be discussed based on their location relative to the allyl silyl ketene acetal. Carbons a to the Cl carbon will be designated Cl, alpha to C4, C4 and so on (Fig. 4.1). 

The diastereofacial selectivity is inconsistent with a Cieplak model, since the crotyl group would have to approach from the side syn to the CT methyl. The low C2, C3 synjanti selectivity could be due to competitive rearrangement via a boat transition state, although it is not obvious why the boat transition state should be of similar energy in this case. 

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