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Efficient Construction of Drug-like Bispirocyclic Scaffolds Via Organocatalytic Cycloadditions of α-Imino γ-Lactones and Alkylidene Pyrazolones
Published on: February 7, 2019
Selectivity control in electron spin inversion processes: regio- and stereochemistry of Paternò-Büchi
Axel G Griesbeck1, Manabu Abe, Samir Bondock
1Institute of Organic Chemistry, University of Cologne, Greinstrasse 4, 50939 Köln, Germany.
Abstract:
Regio- and stereoselectivity in ene-carbonyl photocycloadditions depend on the spin multiplicity of the excited carbonyl state, although both singlet and triplet states produce the cycloadducts with comparable chemoselectivity. The correlation between selectivity and spin state was evaluated by concentration, temperature, and solvent viscosity studies. The higher selectivity observed for triplet reactions is rationalized by the optimal conformations of the intermediate 2-oxabutane-1,4-diyls for intersystem crossing (ISC) to the singlet manifold, controlled preferentially by spin-orbit coupling. This weak interaction connected with ISC can lead to substantial control of regio- and stereoselectivity. The role of hyperfine coupling is demonstrated by magnetic isotope effects.
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