Conformational control allows for [3,3]-sigmatropic rearrangements to proceed with torquoselectivity

摘要

The Woodward-Hoffmann rules determine a first level of selectivity in pericyclic reactions. In this framework torqueselectivity can be defined as an additional degree of selectivity in electrocyclizations favouring one of the two allowed pathways. In this communication we extend this second level of selectivity beyond electrocyclizations. We have designed substrates that undergo a [3,3]-sigmatropic rearrangement in a torqueselective fashion. This behaviour is conformation dependent and is only observed when the reaction proceeds via a boat transition state. Structural design aimed at conformational control at the transition state, ensuring a boat-like structure, provides the first example of a [3,3]-sigmatropic shift that occurs with torqueselectivity.