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In this work, angle strain in a geminally substituted alkene reactant enabled ene–yne metathesis reactions of a wide alkyne and alkene substrate scope. Methylene cyclobutanes and methylene azetidines served as the angle-strained alkene reactants, and both terminal and internal alkynes were found to react. Angle strain results from geometric distortion by the four-membered ring away from the idealized trigonal planar geometry of the sp2 hybridized carbon atom. Highly atom economical ene–yne metathesis reactions were developed using 1:1 reactant stoichiometry and 1 mol % of a Grubbs-type catalyst in most cases. Complete atom economy describes the rare case when all of the atoms of reactants go into the products without any waste, which is an important metric for efficiency and sustainability in organic reactions. In these catalytic reactions, angle strain in the alkene reactant is still present in the 1,3-diene products; therefore, angle strain is not lost in the ene–yne metathesis. The presence of angle strain in 1,3-diene facilitates secondary metathesis and cycloaddition reactions of the 1,3-diene products, showing an activating effect on these subsequent reactions. To better understand how strain facilitates the catalytic reaction, DFT calculations were performed. A cyclic, strained alkene reactant was compared with an acyclic, unstrained reactant to pinpoint the key energetic differences. These studies showed that angle strain enabled an alkene-first initiation step and lowered the activation energy of the alkyne insertion step in the ene–yne metathesis catalytic cycle. A further study in a model system showed that angle strain raised the energy of the reactants and had a less destabilizing effect on key reactive intermediates as well as the cycloaddition and cycloreversion transition states.
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Angle-strained sila-cycloalkynes
Second row elements in small- and medium-rings modulate strain. Herein we report the synthesis of two novel oligosilyl-containing cycloalkynes that exhibit angle-strain, as observed by X-ray crystallography. However, the angle-strained sila-cyclooctynes are sluggish participants in cycloadditions with benzyl azide. A distortion-interaction model analysis based on density functional theory calculations was performed.
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- Award ID(s):
- 2116298
- PAR ID:
- 10504972
- Publisher / Repository:
- Royal Society of Chemistry
- Date Published:
- Journal Name:
- Chemical Communications
- Volume:
- 60
- Issue:
- 36
- ISSN:
- 1359-7345
- Page Range / eLocation ID:
- 4842 to 4845
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D4CC00439F
