Tandem C-C Bond Cleavage of Cyclopropanols and Oxidative Aromatization by Manganese(IV) Oxide in a Direct C-H to C-C Functionalization of Heteroaromatics

Abstract: We report a direct C-H to C-C bond functionalization of electron-deficient heteroaromatics enabled by mild C-C bond cleavage of cyclopropanols as a new route to β-aryl carbonyl-containing products. Additionally, as an alternative to using a "catalyst" that requires an excess amount of a sacrificial oxidant for regeneration and/or oxidative aromatization, this paper features manganese(IV) oxide as an inexpensive "dual role" reagent -effecting both C-C bond cleavage and ultimate rearomatization. Under the specified conditions, a variety o

Determining the predominant tautomeric structure of iodine-based group-transfer reagents by 17O NMR spectroscopy

Cyclic benziodoxole systems have become a premier scaffold for the design of electrophilic transfer reagents. A particularly intriguing aspect is the fundamental II–IIII tautomerism about the hypervalent bond, which has led in certain cases to a surprising re-evaluation of the classic hypervalent structure. Thus, through a combination of 17O NMR spectroscopy at natural abundance with DFT calculations, we establish a convenient method to provide solution-phase structural insights for this class of ubiquitous reagents. In particular, we confirm that Shen’s revised, electrophilic SCF3-transfer reagent also adopts an "acyclic" thioperoxide tautomeric form in solution. After calibration, the approach described herein likely provides a more general and direct method to distinguish between cyclic and acyclic structural features based on a single experimental 17O NMR spectrum and a computationally-derived isotropic shift value. Furthermore, we apply this structural elucidation technique to predict the constitution of an electrophilic iodine-based cyano-transfer reagent as an NC–I–O motif and study the acid-mediated activation of Togni's trifluoromethylation reagent

Oxidative Fluorination of Heteroatoms Enabled by Trichloroisocyanuric Acid and Potassium Fluoride

In synthetic method development, the most rewarding path is seldom a straight line. While our initial entry into pentafluorosulfanyl (SF5) chemistry did not go according to plan (due to inaccessibility of reagents such as SF5Cl at the time), a "detour" led us to establish mild and inexpensive oxidative fluorination conditions that made aryl-SF5 compound synthesis more accessible. The method involved the use of potassium fluoride and trichloroisocyanuric acid (TCICA)-a common swimming pool disinfectant-as opposed to previously employed reagents such as F-2, XeF2, HF, and Cl-2. Thereafter, curiosity led us to explore applications of TCICA/KF as a more general approach to the synthesis of fluorinated Group 15, 16, and 17 heteroatoms in organic scaffolds; this, in turn, prompted SC-XRD, VT-NMR, computational, and physical organic studies. Ultimately, it was discovered that TCICA/KF can be used to synthesize SF5Cl, enabling SF5 chemistry in an unexpected way.ISSN:1433-7851ISSN:1521-3773ISSN:0570-083

Intermolecular Aliphatic C–F···H–C Interaction in the Presence of “Stronger” Hydrogen Bond Acceptors: Crystallographic, Computational, and IR Studies

An unprecedented intermolecular aliphatic C–F···H–C interaction was observed in the X-ray crystal structure of a fluorinated triterpenoid. Despite the notion of fluorine being a poor acceptor, computational and IR studies revealed this interaction to be a weak to moderate hydrogen bond with a C–H stretch vibration frequency blue-shifted by 14 cm^–1 and <i>d</i>(F–H) = 2.13 Å. In addition, the aliphatic C–F bond is the preferred acceptor in the presence of multiple, traditionally <i>stronger</i> oxygen-based hydrogen bond acceptors

Sensitized Aliphatic Fluorination Directed by Terpenoidal Enones: A “Visible Light” Approach

In our continued effort to address the challenges of selective sp³ C–H fluorination on complex molecules, we report a sensitized aliphatic fluorination directed by terpenoidal enones using catalytic benzil and visible light (white LEDs). This sensitized approach is mild, simple to set up, and an economical alternative to our previous protocol based on direct excitation using UV light in a specialized apparatus. Additionally, the amenability of this protocol to photochemical flow conditions and preliminary evidence for electron-transfer processes are highlighted

The Supramolecular Structural Chemistry of Pentafluorosulfanyl and Tetrafluorosulfanylene Compounds

The analysis of crystal structures of SF5‐ or SF4‐containing molecules revealed that these groups are often surrounded by hydrogen or other fluorine atoms. Even though fluorine prefers F⋅⋅⋅H over F⋅⋅⋅F contacts, the latter appeared to be important in many compounds. In a significant number of datasets, the closest F⋅⋅⋅F contacts are below 95 % of the van der Waals distance of two F atoms. Moreover, a number of repeating structural motifs formed by contacts between SF5 groups was identified, including different supramolecular dimers and infinite chains. Among SF4‐containing molecules, the study focused on SF4Cl compounds, including the first solid‐state structure analyses of these reactive species. Additionally, electrostatic potential surfaces of a series of Ph‐SF5 derivatives were calculated, pointing out the substituent influence on the ability of F⋅⋅⋅X contact formation (X=F or other electronegative atom). Interaction energies were calculated for different dimeric arrangements of Ph‐SF5, which were extracted from experimental crystal structure determinations.DFG, 387284271, SFB 1349: Fluorspezifische Wechselwirkungen: Grundlagen und Anwendunge

The Supramolecular Structural Chemistry of Pentafluorosulfanyl and Tetrafluorosulfanylene Compounds

The analysis of crystal structures of SF5‐ or SF4‐containing molecules revealed that these groups are often surrounded by hydrogen or other fluorine atoms. Even though fluorine prefers F⋅⋅⋅H over F⋅⋅⋅F contacts, the latter appeared to be important in many compounds. In a significant number of datasets, the closest F⋅⋅⋅F contacts are below 95 % of the van der Waals distance of two F atoms. Moreover, a number of repeating structural motifs formed by contacts between SF5 groups was identified, including different supramolecular dimers and infinite chains. Among SF4‐containing molecules, the study focused on SF4Cl compounds, including the first solid‐state structure analyses of these reactive species. Additionally, electrostatic potential surfaces of a series of Ph‐SF5 derivatives were calculated, pointing out the substituent influence on the ability of F⋅⋅⋅X contact formation (X=F or other electronegative atom). Interaction energies were calculated for different dimeric arrangements of Ph‐SF5, which were extracted from experimental crystal structure determinations.ISSN:0947-6539ISSN:1521-376

Triethylborane-Initiated Radical Chain Fluorination: A Synthetic Method Derived from Mechanistic Insight

We offer a mild, metal-free sp³ C–H fluorination alternative using Selectfluor and a substoichiometric amount of triethylboranean established radical initiator in the presence of O₂. This radical-chain-based synthetic method is particularly noteworthy as an offspring of the insight gained from a mechanistic study of copper-promoted aliphatic fluorination, constructively turning O₂ from an enemy to an ally. Furthermore, BEt₃/O₂ is a preferred initiator in industrial processes, as it is economical, is low in toxicity, and lends way to easier workup