We examine the effects of fusing two benzofurans to s-indacene (indacenodibenzofurans,I DBFs) and dicyclopenta[b,g]naphthalene (indenoindenodibenzofurans, IIDBFs) to control the strong antiaromaticity and diradical character of these core units.S ynthesis via 3-functionalized benzofuran yields syn-IDBF and syn-IIDBF.s yn-IDBF possesses ah igh degree of paratropicity,e xceeding that of the parent hydrocarbon, which in turn results in strong diradical character for syn-IIDBF.I nt he case of the anti-isomers, synthesized via 2-substituted benzofurans,t hese effects are decreased;h owever,b oth derivatives undergo an unexpected ring-opening reaction during the final dearomatization step. All the results are compared to the benzothiophene-fused analogues and showt hat the increased electronegativity of oxygen in the syn-fused derivatives leads to enhancement of the antiaromatic core causing greater paratropicity.F or syn-IIDBF increased diradical character results from rearomatization of the core naphthalene unit in order to relieve this paratropicity.
Tuning strained alkyne reactivity via organic synthesis has evolved into a burgeoning field of study largely focused on cyclooctyne, wherein physical organic chemistry helps guide rational molecular design to produce...
Strain has a unique and sometimes unpredictable impact
on the properties and reactivity of molecules. To thoroughly describe strain in
molecules, a computational tool that relates strain to reactivity by localizing
and quantifying strain was developed. Strain is calculated local to every coordinate
in the molecule and areas of higher strain are shown experimentally to be more
reactive. Not only does this tool directly compare strain in parts of the same
molecule, but it also computes total strain to give a full picture of molecular
strain. It is freely available to the public on GitHub under the name StrainViz
and much of the workflow is automated to simplify use for non-experts. Unique
insight into the reactivity of curved aromatic molecules and strained alkyne
bioorthogonal reagents is described within.
We examine the effects of fusing two benzofurans to s‐indacene (indacenodibenzofurans, IDBFs) and dicyclopenta[b,g]naphthalene (indenoindenodibenzofurans, IIDBFs) to control the strong antiaromaticity and diradical character of these core units. Synthesis via 3‐functionalized benzofuran yields syn‐IDBF and syn‐IIDBF. syn‐IDBF possesses a high degree of paratropicity, exceeding that of the parent hydrocarbon, which in turn results in strong diradical character for syn‐IIDBF. In the case of the anti‐isomers, synthesized via 2‐substituted benzofurans, these effects are decreased; however, both derivatives undergo an unexpected ring‐opening reaction during the final dearomatization step. All the results are compared to the benzothiophene‐fused analogues and show that the increased electronegativity of oxygen in the syn‐fused derivatives leads to enhancement of the antiaromatic core causing greater paratropicity. For syn‐IIDBF increased diradical character results from rearomati‐zation of the core naphthalene unit in order to relieve this paratropicity.
Tuning strained alkyne reactivity via organic synthesis has evolved into a burgeoning field of study largely focused on cyclooctyne, wherein physical organic chemistry helps guide rational molecular design to produce molecules with intriguing properties. Concurrent research in the field of carbon nanomaterials has produced new types of strained alkyne macrocycles, such as cycloparaphenyleneacetylenes, that possess uniquely curved aromatic π systems but hover on the edge of stability. In 2018, we introduced a strained alkyne scaffold that marries the synthetic accessibility and stability of cyclooctyne with the curved π system of carbon nanomaterials. These molecules are strained alkyne-containing cycloparaphenylenes (or [n+1]CPPs), which have been shown to possess size-dependent reactivity as well as the classic characteristics of the unfunctionalized parent CPP, such as a tunable HOMO-LUMO gap and bright fluorescence for large sizes. Herein, we elaborate further on this scaffold, introducing two modifications to the original design and fully characterizing the kinetics of the strain-promoted azide-alkyne cycloaddition (SPAAC) for each [n+1]CPP with a model azide. Additionally, we explain how electronic (the incorporation of fluorine atoms) and strain (a meta linkage which heightens local strain at the alkyne) modulations affect SPAAC reactivity via the distortion-interaction computational model. Altogether, these results indicate that through a modular synthesis and rational chemical design, we have developed a new family of tunable and inherently fluorescent strained alkyne carbon nanomaterials.
Strain has a unique and sometimes unpredictable impact
on the properties and reactivity of molecules. To thoroughly describe strain in
molecules, a computational tool that relates strain to reactivity by localizing
and quantifying strain was developed. Strain is calculated local to every coordinate
in the molecule and areas of higher strain are shown experimentally to be more
reactive. Not only does this tool directly compare strain in parts of the same
molecule, but it also computes total strain to give a full picture of molecular
strain. It is freely available to the public on GitHub under the name StrainViz
and much of the workflow is automated to simplify use for non-experts. Unique
insight into the reactivity of curved aromatic molecules and strained alkyne
bioorthogonal reagents is described within.
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