@article {32712, title = {Selecting Chiral BINOL-Derived Phosphoric Acid Catalysts: General Model To Identify Steric Features Essential for Enantioselectivity}, journal = {Chemistry {\textendash} A European Journal}, volume = {23}, year = {2017}, pages = {14248-14260}, abstract = {
Abstract Choosing the optimal catalyst for a new transformation is challenging because the ideal molecular requirements of the catalyst for one reaction do not always simply translate to another. Large groups at the 3,3\′ positions of the binaphthol rings are important for efficient stereoinduction but if they are too large this can lead to unusual or poor results. By applying a quantitative steric assessment of the substituents at the 3,3\′ positions of the binaphthol ring, we have systematically studied the effect of modulating this group on enantioselectivity for a wide range of reactions involving imines, and verified this analysis using ONIOM calculations. We have shown that in most reactions, the stereochemical outcome depends on both proximal and remote sterics. Summarising detailed calculations into a simple qualitative model identifies and explains the steric features required for high selectivity. This model is consistent with seventy seven papers reporting reactions (over 1000 transformations in total), and provides a straightforward decision tree for selecting the best catalyst.
}, keywords = {ASYMMETRIC CATALYSIS, binaphthol, catalyst choice, chirality, phosphoric acid}, doi = {10.1002/chem.201702019}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/chem.201702019}, author = {Reid, Jolene P. and Goodman, Jonathan M.} } @article {1145, title = {Discrimination in the solid-state photodimerization of 1-methyl-5,6-diphenylpyrazin-2-one}, journal = {European Journal of Organic Chemistry}, number = {5}, year = {2005}, note = {ISI Document Delivery No.: 903LHTimes Cited: 5Cited Reference Count: 18}, month = {Feb}, pages = {847-853}, type = {Article}, abstract = {1-Methyl- and 1-ethyl-5,6-diphenylpyrazin-2-one crystallize in two modifications, one of which is light-stable and the other light-sensitive. The light-sensitive modification is known to undergo photodimerization in the solid state. This polymorph crystallizes in the monoclinic space group P2(1) with two crystallographically independent molecules in the asymmetric unit. The molecules are packed in stacks running parallel to the unique b axis. The two independent molecules are arranged alternately along the stack. In principle, there are two different pairs of molecules within a stack that can undergo photodimerization, and each should form a different enantiomer. A large crystal was irradiated and a solution of the product was separated by HPLC. The optical purity of the (+)-enantiomer sample was estimated to be greater than 90 \%. This finding indicates that only one of the two pairs undergoes photoreaction. The structure of a single crystal of the pyrazinone was elucidated by X-ray diffractometry before and after irradiation with a laser at a wavelength of 488 nm to 19 \% conversion. The results of the crystal-structure determinations provide additional evidence that only one of the two pairs of molecules undergoes photodimerization although there are no significant differences between the distances between the reacting centers. Furthermore, the latter results suggest that weak hydrogen bonds are a dominant factor that determines which of the two pairs is dimerized upon irradiation. ((C) Wiley-VCH Verlag GmbH \& Co. KGaA, 69451 Weinheim, Germany, 2005).}, keywords = {chirality, crystal structure, DIMERIZATION, enantioselectivity, PHOTOCHEMISTRY, SINGLE-CRYSTAL PHOTODIMERIZATION, solid-state reactions}, isbn = {1434-193X}, url = {