title: A Bio-Inspired, Catalytic E → Z Isomerization of Activated Olefins.
abstract: Herein, Nature's flavin-mediated activation of complex (poly)enes has been translated to a small molecule paradigm culminating in a highly (Z)-selective, catalytic isomerization of activated olefins using (-)-riboflavin (up to 99:1 Z/E). In contrast to the prominent Z → E isomerization of the natural system, it was possible to invert the directionality of the isomerization (E → Z) by simultaneously truncating the retinal scaffold, and introducing a third olefin substituent to augment A1,3-strain upon isomerization. Consequently, conjugation is reduced in the product chromophore leading to a substrate/product combination with discrete photophysical signatures. The operationally simple isomerization protocol has been applied to a variety of enone-derived substrates and showcased in the preparation of the medically relevant 4-substituted coumarin scaffold. A correlation of sensitizer triplet energy (ET) and reaction efficiency, together with the study of additive effects and mechanistic probes, is consistent with a triplet energy transfer mechanism.
authors: Institute for Organic Chemistry, Westfälische Wilhelms-Universität Münster , Corrensstrasse 40, 48149 Münster, Germany.
authors: Jan B
authors: JB
authors: Metternich
authors: Institute for Organic Chemistry, Westfälische Wilhelms-Universität Münster , Corrensstrasse 40, 48149 Münster, Germany.
authors: Ryan
authors: R
authors: Gilmour
mesh_terms: D000475:Alkenes / Q000737:chemistry*; D032701:Biomimetics; D002384:Catalysis; D003374:Coumarins / Q000737:chemistry; D003500:Cyclization; D012256:Riboflavin / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: D000475:Alkenes; D003374:Coumarins; C030123:coumarin; D012256:Riboflavin