Boron-enabled geometric isomerization of alkenes via selective energy-transfer catalysis

An E-Z boron swivel Compounds with carbon-carbon double bonds can form two distinct isomers, depending on whether the heaviest substituents on both carbons lie on the same side (labeled Z) or diagonally across from each other (labeled E). Molloy et al. present a convenient method to reorient double...

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Published in:Science (American Association for the Advancement of Science) 2020-07, Vol.369 (6501), p.302-306
Main Authors: Molloy, John J., Schäfer, Michael, Wienhold, Max, Morack, Tobias, Daniliuc, Constantin G., Gilmour, Ryan
Format: Article
Language:English
Subjects:
Alkenes
Atom economy
Boron
Boron compounds
Carbon
Carbonyl compounds
Carbonyls
Catalysis
Chemical bonds
Chromophores
Energy transfer
Gating
Isomerization
Isomers
Molecular weight
Photosensitization
Polyenes
Retinoic acid
Substrates
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Summary:An E-Z boron swivel Compounds with carbon-carbon double bonds can form two distinct isomers, depending on whether the heaviest substituents on both carbons lie on the same side (labeled Z) or diagonally across from each other (labeled E). Molloy et al. present a convenient method to reorient double bonds that bear boron and carbonyl substituents. When they are diagonally opposed, both substituents stay in plane, and the double bond is easily swiveled by photosensitization. However, once on the same side as the carbonyl, the boron rotates out of plane and further sensitization is inhibited. Science this issue p. 302 Rotation of a boron substituent biases photosensitized isomerization of a carbon-carbon double bond in just one direction. Isomerization-based strategies to enable the stereodivergent construction of complex polyenes from geometrically defined alkene linchpins remain conspicuously underdeveloped. Mitigating the thermodynamic constraints inherent to isomerization is further frustrated by the considerations of atom efficiency in idealized low–molecular weight precursors. In this work, we report a general ambiphilic C 3 scaffold that can be isomerized and bidirectionally extended. Predicated on highly efficient triplet energy transfer, the selective isomerization of β-borylacrylates is contingent on the participation of the boron p orbital in the substrate chromophore. Rotation of the C(sp 2 )–B bond by 90° in the product renders re-excitation inefficient and endows directionality. This subtle stereoelectronic gating mechanism enables the stereocontrolled syntheses of well-defined retinoic acid derivatives.
ISSN:0036-8075
1095-9203
DOI:10.1126/science.abb7235