An Asymmetric Ortholithiation Approach to Inherently Chiral Calix[4]arenes

A general asymmetric synthesis of inherently chiral calix[4]arenes is described: using a chiral oxazoline derived from l-valine, an ortholithiation strategy is employed to give inherently chiral calix[4]arenes with high (93%) enantiomeric excesses. A crystal structure of a phosphine oxide intermediate has been obtained, unambiguously assigning the major diastereomer in the reaction; a mechanism explaining this result is proposed.