This communication describes a mild, amide-directed fluorination of benzylic, allylic, and unactivated C-H bonds mediated by iron. Upon exposure to a catalytic amount of iron(II) triflate (Fe(OTf)), N-fluoro-2-methylbenzamides undergo chemoselective fluorine transfer to provide the corresponding fluorides in high yield. The reaction demonstrates broad substrate scope and functional group tolerance without the use of any noble metal additives. Mechanistic and computational experiments suggest that the reaction proceeds through short-lived radical intermediates with F-transfer mediated directly by iron.

The conformations of a series of benziporphyrins, naphthiporphyrins, oxybenziporphyrins, and related structures were minimized using DFT-B3LYP/6-311++G(d,p). The relative stabilities of the tautomers for each series were calculated using M06-2X and B3LYP-D functionals, and bond lengths were obtained. The diatropic properties of each species were assessed by calculating nucleus independent chemical shifts (NICS) and the related NICSzz values. Although benziporphyrin and naphthiporphyrin tautomers essentially exhibit no aromatic properties, mono- and diprotonated species show weakly diatropic characteristics in agreement with experimental observations. Benziphlorins, intermediates in the MacDonald "3 + 1" synthesis of benziporphyrins, were also examined and tautomers with methylene units adjacent to the benzene ring were shown to be far more stable than tautomers with a CH2 bridge between two pyrrolic units. 2-Hydroxybenziporphyrin was shown to be significantly less stable than the aromatic tautomer oxybenziporphyrin, although diprotonation leads to a species with somewhat reduced diatropicity. Related systems were also analyzed and the results demonstrate that benziporphyrins and naphthiporphyrins range from structures with no measurable macrocyclic aromaticity to strongly aromatic systems that exhibit large diamagnetic ring currents.

An adj-dicarbaporphyrin was prepared by carrying out a base-catalyzed MacDonald reaction between bis(3-indenyl)methane and a dipyrrylmethane dialdehyde. The porphyrinoid system exhibited highly diatropic characteristics, and the proton NMR spectrum gave resonances at -5.74 and -6.24 ppm for the internal NH and CH protons, respectively. The UV-vis spectrum was also porphyrin-like, giving a Soret band at 455 nm and a series of Q bands at longer wavelengths. Addition of trifluoroacetic acid gave a C-protonated monocation, and at higher acid concentrations a dicationic species was observed. Addition of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) afforded a monodeprotonated porphyrinoid anion. All of these species retained highly diatropic characteristics. Density functional theory calculations showed that a nonplanar tautomer with four internal hydrogens was favored, in agreement with the spectroscopic data. Nucleus-independent chemical shift calculations also confirmed the aromatic characteristics of the free-base, cationic, and anionic structures. The dicarbaporphyrin reacted with palladium(II) acetate in refluxing acetonitrile to give an unusual tripalladium sandwich complex consisting of two dianionic palladium(II) dicarbaporphyrin units surrounding a palladium(IV) cation with unique η(5) interactions involving meso-carbon atoms.

The installation of trifluoromethyl groups has become an essential step across a number of industries such as agrochemicals, drug discovery, and materials. Consequently, the rapid introduction of this critical functional group in a predictable fashion would benefit current practitioners in those fields. This communication describes a mild trifluoromethylation of benzylic C−H bonds with high selectivity for the least hindered hydrogen atom. The reaction provides monotrifluoromethylation and proceeds in an environmentally friendly acetone/water solvent system. The method can be used to install benzylic trifluoromethyl groups on highly functionalized drug molecules.

Monocarbaporphyrins, dicarbaporphyrins, tricarbaporphyrins, and quatyrins can all potentially exist in a number of tautomeric forms, but little is known about these species. In addition, no examples of tricarbaporphyrins or quatyrins are known at this time. In order to get information on the relative stabilities of carbaporphyrin tautomers, a series of aromatic and nonaromatic structures were assessed using computational methods. The conformations of 41 carbaporphyrin structures, together with four tautomers of porphyrin and the related antiaromatic species didehydroquatyrin, were minimized using DFT-B3LYP/6-311++G(d,p). The relative stabilities of the tautomers for each series were computed, and the bond lengths and bond angles were calculated. Many aromatic carbaporphyrin structures have very crowded cavities with up to six hydrogens being present. However, this was not sufficient to destabilize the aromatic structures relative to the nonaromatic forms. Furthermore, nucleus-independent chemical shifts (NICS) demonstrated that all of the porphyrinoids with 18-π-electron delocalization pathways are highly diatropic. adj-Dicarbaporphyrin and tricarbaporphyrin favor tautomers with an internal methylene group, while two interior methylenes are present in the favored tautomers for quatyrin. The results provide valuable information that will be helpful in designing synthetic routes to higher carbaporphyrinoid systems.

Electrospray ionization (ESI) combined with ion mobility spectrometry (IMS) and mass spectrometry (MS) techniques is used to examine the Biginelli reaction in an ensemble of ions generated from droplets.

The conformations of eight neo-confused porphyrin (neo-CP) structures and seven related benzo-neo-confused porphyrins (B-neo-CPs) were minimized using DFT-B3LYP/6-311++G(d,p). In addition, in order to provide contrasts to the B-neo-CP tautomers, a series of twelve benzoporphyrin (BP) tautomers and twelve benzocarbaporphyrins (BCPs) were also analyzed, and two N-confused porphyrin (NCP) tautomers were also considered. The relative stability of the tautomers for each series was computed, and the bond lengths and bond angles were calculated. Surprisingly, all of the neo-CP and B-neo-CP tautomers were near planar. The fully conjugated members of these series showed a significant degree of bond length alternation, unlike porphyrins or the aromatic forms of NCP, BP or BCP. The most stable tautomer of neo-CP was calculated to be 27.04 kcal mol(-1) higher in energy than porphyrin and 9.95 kcal mol(-1) higher in energy than the most favored NCP tautomer. The most stable tautomer of B-neo-CP was similarly shown to be 26.40 kcal mol(-1) higher in energy than benzoporphyrin. The favored tautomers also place the internal NH opposite to the neo-confused ring to minimize steric and lone pair-lone pair interactions, and to provide improved hydrogen bonding interactions. Nucleus independent chemical shifts (NICS) demonstrated that the fully conjugated neo-CP and B-neo-CP tautomers exhibit a significant amount of diatropic character, but these values are somewhat lower than the results obtained for porphyrins, BPs or BCPs. BCPs have three internal hydrogens, but the favored tautomer places the two pyrrolic hydrogens on each side of the indene unit to maximize hydrogen bonding interactions. Tautomers with an internal CH2 unit are also feasible, but these are energetically less favorable, have reduced diatropicity, and show significant bond length alternation. The results indicate that 18π electron delocalization pathways that pass through a fused benzene ring are less favorable than alternative delocalization pathways that bypass this unit.

Oxidation of tetraarylazuliporphyrins with silver(I) acetate in refluxing chloroform-acetonitrile afforded good yields of 21-oxyazuliporphyrins. Although hydroxyazuliporphyrin tautomers can be considered for this system, spectroscopic results and density functional theory calculations indicate that the keto form is favored, and this was confirmed by single-crystal X-ray diffraction. Oxyazuliporphyrins formally possess a 24π electron delocalization pathway, but the proton NMR spectra are consistent with macrocycles that have diatropic ring currents. Nucleus independent chemical shift and anisotropy of induced current density calculations also confirmed the diatropic nature of these macrocycles, although these results indicated that the seven-membered ring is antiaromatic. However, while the NMR spectra showed the azulene protons at atypically high field values, the results are consistent with a nonaromatic cycloheptatrienyl unit. Protonation gave dicationic products that exhibited enhanced diatropic character. Oxyazuliporphyrins readily form metalated derivatives with Ni(II), Pd(II), and Pt(II), and these complexes exhibited significant diatropic character even though the macrocycle is highly distorted. X-ray diffraction characterization of palladium(II) and platinum(II) complexes demonstrated that these derivatives are structurally virtually identical to a previously reported copper(II) oxyazuliporphyrin.