Origins of Stereoselectivity in Chiral Aminoalcohol Catalysis of Oxyallyl Cation-Indole Reactions

Amino alcohol-derived chiral stationary phases

An updated minireview of chiral stationary phases (CSPs) based on amino alcohols is presented. In this minireview, we focused on amino alcohols as starting materials in preparation of chiral catalysts for asymmetric organic synthesis and CSPs for chiral separations. Among the various CSPs, we summarized the important developments and applications of the amino alcohol-based Pirkle-type CSPs, ligand exchange CSPs, α-amino acid-derived amino alcohol CSPs, and symmetric CSPs from their first appearance to the present day to propose ideas for the development of new CSPs with improved performance.

Origins of Selective Formation of 5-Vinyl-2-methylene Furans from Oxyallyl/Diene (3+2) Cycloadditions with Pd(0) Catalysis

The (3+2) cycloadditions between electron-deficient Pd-oxyallyls and conjugated dienes have been investigated with density functional theory calculations. A stepwise mechanism with C-C bond formation occurring first is supported by computations. The key electron-withdrawing ester substituent on the Pd-oxyallyl species decreases the migratory insertion barrier by both lowering the LUMO energy and enabling a less-strained six-membered coordination mode. The lack of (3+2) reactivity with monoenes is attributed to higher migratory insertion barriers due to a lower-energy HOMO, as well as high C-O reductive elimination barriers, which become rate-determining. Conjugated dienes enable the formation of a highly electrophilic η³ Pd-allyl species and greatly facilitates C-O formation.