Claisen rearrangement suprafacial geometry

The Cope rearrangement and the Claisen rearrangement involve reorganization of an odd number of electron pairs and proceed by suprafacial geometry. 

The suprafacial nature of the Claisen rearrangement means that for 4,6 rearrangements of cyclic allylic alcohols the new C —C bond is formed eis to the original C —O bond. The double-bond geometry is, by necessity, Z for a short tethered chain. 

The Claisen rearrangement is a suprafacial, concerted, nonsynchronous pericyclic process that is considered occasionally as an intramolecular 8, 2 alkylation (Eq. 3.1.18) [2]. When the Claisen rearrangement can produce enantiotopic faces at both terminals of allyl vinyl ether, the rearrangement can proceed through two pairs of chiral transition states to prepare two racemic diastereomers bearing newly created stereocenters of the products 15 and 16 (Eq. 3.1.19). Achiral allyl vinyl ether 14 can provide two enantiomeric chair-like transition states chair 1 and 2, both of which lead to the racemic, diastereomeric aldehyde 15. Similarly, the enantiomeric boat-like transition states boat 1 and 2 provide racemic diastereomer 16. The two transition states are essentially different in energy and the ratio 15/16 reflects the transition state geometry. 

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