Near-Infrared Light Activated Azo-BF₂ Switches

Increasing the electron density in BF₂-coodinated azo compounds through <i>para</i>-substitution leads to a bathochromic shift in their activation wavelength. When the substituent is dimethyl amine, or the like, the <i>trans</i>/<i>cis</i> isomerization process can be efficiently modulated using near infrared light. The electron donating capability of the substituent also controls the hydrolysis half-life of the switch in aqueous solution, which is drastically longer for the <i>cis</i> isomer, while the BF₂-coodination prevents reduction by glutathione

Dearomative Indole (3 + 2) Cycloaddition Reactions

A diastereoselective (3 + 2) dearomative annulation of 3-substituted indoles with α-haloketones has been developed. Significant regiochemical control was observed. This methodology provides easy access to highly functionalized cyclopenta- or cyclohexa-fused indoline compounds, which are common structures of many natural products. The synthetic potential of this reaction was demonstrated in the concise syntheses of the core structures of vincorine, isocorymine, and aspidophylline A. DFT studies (B3LYP-D3/6-311++G**/MeOH) on cyclization mechanisms involving the 2-hydroxyallyl cation and its deprotonated oxyallyl cation have been performed. Under the reaction conditions, with a sparingly soluble Na₂CO₃ base, both species may be present and both pathways are viable. Both pathways support the formation of the experimentally observed <i>O</i>-bound intermediate, its transformation to the final product, the regiochemical and eventual stereochemical outcome of the kinetic cyclization product, and the thermodynamic preference for formation of the final stereoisomer

Near-Infrared Light Activated Azo-BF₂ Switches

Increasing the electron density in BF₂-coodinated azo compounds through <i>para</i>-substitution leads to a bathochromic shift in their activation wavelength. When the substituent is dimethyl amine, or the like, the <i>trans</i>/<i>cis</i> isomerization process can be efficiently modulated using near infrared light. The electron donating capability of the substituent also controls the hydrolysis half-life of the switch in aqueous solution, which is drastically longer for the <i>cis</i> isomer, while the BF₂-coodination prevents reduction by glutathione

Visible Light Switching of a BF₂‑Coordinated Azo Compound

Here we report the synthesis and characterization of a BF₂–azo complex that can be induced to isomerize without the need of deleterious UV light. The complexation of the azo group with BF₂, coupled with the extended conjugation of the NN π-electrons, increases the energy of the n−π* transitions and introduces new π-nonbonding (π_nb) to π* transitions that dominate the visible region. The well separated π_nb–π* transitions of the <i>trans</i> and <i>cis</i> isomers enable the efficient switching of the system by using only visible light. The complexation also leads to a slow <i>cis</i> → <i>trans</i> thermal relaxation rate (<i>t</i>_1/2 = 12.5 h). Theoretical calculations indicate that the absorption bands in the visible range can be tuned using different Lewis acids, opening the way to a conceptually new strategy for the manipulation of azo compounds using only visible light

Dearomative Indole (3 + 2) Cycloaddition Reactions

A diastereoselective (3 + 2) dearomative annulation of 3-substituted indoles with α-haloketones has been developed. Significant regiochemical control was observed. This methodology provides easy access to highly functionalized cyclopenta- or cyclohexa-fused indoline compounds, which are common structures of many natural products. The synthetic potential of this reaction was demonstrated in the concise syntheses of the core structures of vincorine, isocorymine, and aspidophylline A. DFT studies (B3LYP-D3/6-311++G**/MeOH) on cyclization mechanisms involving the 2-hydroxyallyl cation and its deprotonated oxyallyl cation have been performed. Under the reaction conditions, with a sparingly soluble Na₂CO₃ base, both species may be present and both pathways are viable. Both pathways support the formation of the experimentally observed <i>O</i>-bound intermediate, its transformation to the final product, the regiochemical and eventual stereochemical outcome of the kinetic cyclization product, and the thermodynamic preference for formation of the final stereoisomer

Visible Light Switching of a BF₂‑Coordinated Azo Compound

Here we report the synthesis and characterization of a BF₂–azo complex that can be induced to isomerize without the need of deleterious UV light. The complexation of the azo group with BF₂, coupled with the extended conjugation of the NN π-electrons, increases the energy of the n−π* transitions and introduces new π-nonbonding (π_nb) to π* transitions that dominate the visible region. The well separated π_nb–π* transitions of the <i>trans</i> and <i>cis</i> isomers enable the efficient switching of the system by using only visible light. The complexation also leads to a slow <i>cis</i> → <i>trans</i> thermal relaxation rate (<i>t</i>_1/2 = 12.5 h). Theoretical calculations indicate that the absorption bands in the visible range can be tuned using different Lewis acids, opening the way to a conceptually new strategy for the manipulation of azo compounds using only visible light

Dearomative Indole (3 + 2) Reactions with Azaoxyallyl Cations – New Method for the Synthesis of Pyrroloindolines

Herein, we report the first examples of the synthesis of pyrroloindolines by means of (3 + 2) dearomative annulation reactions between 3-substituted indoles and highly reactive azaoxyallyl cations. Computational studies using density functional theory (DFT) (B3LYP-D3/6-311G**++) support a stepwise reaction pathway in which initial C–C bond formation takes place at C3 of indole, followed by ring closure to give the observed products. Insights gleaned from these calculations indicate that the solvent, either TFE or HFIP, can stabilize the transition state through H-bonding interactions with oxygen of the azaoxyallyl cation and other relevant intermediates, thereby increasing the rates of these reactions

What Controls Regiochemistry in 1,3-Dipolar Cycloadditions of Münchnones with Nitrostyrenes?

The distinct experimentally observed regiochemistries of the reactions between mesoionic münchnones and β-nitrostyrenes or phenylacetylene are shown by DFT/BDA/ETS-NOCV analyses of the transition states to be dominated by steric and reactant reorganization factors, rather than the orbital overlap considerations predicted by Frontier Molecular Orbital (FMO) Theory

Cyanide Detection Using a Triazolopyridinium Salt

A triazolopyridinium salt chemodosimeter has been developed that displays a 60-fold enhancement in fluorescence upon reaction with cyanide. The novel, fast, selective and sensitive reaction-based indicator relies on the pseudopericyclic ring opening of the bridgehead nitrogen-containing detector

Synthesis, Reactivity, and Resolution of a <i>C</i>₂–Symmetric, P–Stereogenic Benzodiphosphetane, a Building Block for Chiral Bis(phosphines)

Although the pyramidal inversion barriers in diphosphines (R₂P–PR₂) are similar to those in phosphines (PR₃), P-stereogenic chiral diphosphines have rarely been exploited as building blocks in asymmetric synthesis. The synthesis, reactivity, and resolution of the benzodiphosphetane <i>trans</i>-1,2-(P(<i>t</i>-Bu))₂C₆H₄ are reported. Alkylation with MeOTf followed by addition of a nucleophile gave the useful <i>C</i>₂-symmetric P-stereogenic ligand BenzP* and novel analogues