Asymmetric Induction during Yang Cyclization of α-Oxoamides:  The Power of a Covalently Linked Chiral Auxiliary Is Enhanced in the Crystalline State

Abstract

γ-Hydrogen abstraction has been revealed to be the primary photoprocess in the crystalline state of α-oxoamides through photochemical and X-ray structural studies. The outstanding ability of a covalent chiral auxiliary in generating asymmetric induction in the photoproduct β-lactam has been established with 10 examples. We have shown that the crystal lattice preorganizes the reactant molecules toward a single diastereomer of the β-lactam and prevents large motions of the 1,4-diradical intermediate that would result in the loss of stereochemical memory. A rare single-crystal-to-single-crystal transformation path of one of the examples investigated establishes the direct correlation between the stereochemistries of the reactant and the product