Provided is a photochromic indolenaphthopyran compound having the skeletal structure of Formula (I): wherein R1 and R2 each independently have a steric bulk A, wherein at least one of R1 or R2 has a steric bulk A of at least 0.6, R3 and R4 each independently have a Hammett σρ value, and wherein the indolenaphthopyran compound has a calculated electronic steric factor of at least -3.3.
Nickel-Catalyzed Asymmetric Kumada Cross-Coupling of Symmetric Cyclic Sulfates
作者:Meredith S. Eno、Alexander Lu、James P. Morken
DOI:10.1021/jacs.6b03384
日期:2016.6.29
Nickel-catalyzed enantioselective cross-couplings between symmetric cyclic sulfates and aromatic Grignard reagents are described. These reactions are effective with a broad range of substituted cyclic sulfates and deliver products with asymmetric tertiary carbon centers. Mechanistic experiments point to a stereoinvertive SN2-like oxidative addition of a nickel complex to the electrophilic substrate
that attractive dispersion forces may be responsible for a change of the binding mode. The catalytic [2+2] photocycloaddition was shown to proceed on the triplet hypersurface with a quantum yield of 0.05. The positive effect of Lewis acids on the outcome of a given intramolecular [2+2] photocycloaddition was illustrated by optimizing the key step in a concise total synthesis of the sesquiterpene (±)‐italicene