Asymmetric induction during Yang cyclization of alpha-oxoamides: the power of a covalently linked chiral auxiliary is enhanced in the crystalline state.

Gamma-hydrogen abstraction has been revealed to be the primary photoprocess in the crystalline state of alpha-oxoamides through photochemical and X-ray structural studies. The outstanding ability of a covalent chiral auxiliary in generating asymmetric induction in the photoproduct beta-lactam has been established with 10 examples. We have shown that the crystal lattice preorganizes the reactant molecules toward a single diastereomer of the beta-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.