A series of differently substituted β-enaminones 2a,b, 4a–i, 8a–d, and 9–13, their BF2-β-ketoiminate complexes 5a–d, and BF2-β-diketonate complexes 6a–d were prepared as model substrates for photochemical transformations. The attempted photochemical transformations of enaminones 2, 4, 8 and BF2-β-ketoiminate complexes 5 failed. On the other hand, irradiation of mixtures of BF2-β-diketonate complexes 6a–d and cycloalkanes with UV-A light (365 nm) gave the corresponding De Mayo reaction products 7a–f in 9–30% yields. The photochemical ring-expansion of acetyl tetralone-derived BF2-complex 6d gave novel diannulated cyclooctane derivatives 7e and 7f, which would be difficult to obtain using conventional cyclization methods.

A four-step synthesis process of bifunctional, noncovalent organocatalysts based on the chiral (1R,2R)-cyclohexane-1,2-diamine scaffold containing a 1,2-benzenediamine H-bond donor was developed. Nucleophilic aromatic substitution of the 2-fluoronitrobenzene derivative with the commercial (1R,2R)-cyclohexane-1,2-diamine was followed by selective alkylation of the primary amino group, reduction of the aromatic nitro group and final derivatization of the primary aromatic amino group, i.e., acylation, sulfonation, reductive alkylation and arylation, leading to the four subtypes of organocatalysts. All new compounds were fully characterized. The prepared organocatalysts (32 examples) were tested in the Michael addition of acetylacetone to trans-β-nitrostyrene, yielding the addition product with incomplete conversions (up to 93%) and enantioselectivities of up to 41% ee.

Four bifunctional, noncovalent amine-squaramide organocatalysts were prepared from camphor in five steps. The stereochemistry of the prepared catalysts was thoroughly analyzed using various spectroscopic techniques. Their organocatalytic activity was investigated in the Michael addition of acetylacetone to trans-β-nitrostyrene. The addition product was formed in complete conversion and with an enantioselectivity of up to 77% ee. In the reactions catalyzed by the 2-exo-3-endo catalysts, the major (S)-enantiomer was formed, whereas in the presence of 2-endo-3-endo catalysts, the (R)-enantiomer was formed as the major product.

Sulfonyl chlorides are a synthetically attractive source of sulfonyl radicals in photoredox catalysis and are useful precursors in the synthesis of sulfones. Sulfamoyl chlorides, on the other hand, remain poorly represented despite their similar potential. In this study, N-chlorosulfonylated beta-lactams were prepared from readily available precursors and utilized in an atom transfer radical addition (ATRA) reaction with a variety of olefins, producing beta-lactam sulfonamides in 49-95% yields. beta-Lactams fused to a dihydro-1,2-thiazine ring which closely resemble carbacephems, a widely used class of antibiotics, were also synthesized by an intra-molecular ATRA reaction. This methodology enables the preparation of beta-lactam sulfonamides, a class of compounds that are of great interest in pharmacology. image

A novel methodology for the synthesis of 2-pyridones bearing a 2-pyridyl group on nitrogen and carbon atoms, starting from 2-bromopyridines, was developed employing a simple Ru(II)–KOPiv–Na2CO3 catalytic system. Unsubstituted 2-bromopyridine was successfully converted to the penta-heteroarylated 2-pyridone product using this method. Preliminary mechanistic studies revealed a possible synthetic pathway leading to the multi-heteroarylated 2-pyridone products, involving consecutive oxygen incorporation, a Buchwald–Hartwig-type reaction, and C–H bond activation.

We report new sequential wavelength‐selective photochemical transformations of 1‐alkenylpyrazolo[1,2‐a]pyrazolones to pyrazolo[1,2‐a][1,2]diazepines or cyclobuta[c]pyrazolo[1,2‐a]pyrazolones. Irradiation of 1‐alkenylpyrazolo[1,2‐a]pyrazolones with visible‐light (blue LED, 457 nm) induced selective ‘ring switching’ transformation into pyrazolo[1,2‐a][1,2]diazepines, which, upon irradiation with UV A light (black LED, 365 nm) underwent electrocyclisation into cyclobuta[c]pyrazolo[1,2‐a]pyrazolones. Due to the very narrow irradiation wavelength now available from OLED sources, the selective formation of either 5,7‐bicyclic or 5,5,4‐tricyclic ring systems from the 5,5‐bicyclic starting material is possible simply by changing the wavelength of the irradiation source. The transformations took place under mild conditions in the absence of additives or photocatalysts. Mechanistic studies indicate that these transformations proceed through the formation of an excited triplet state of the substrate, followed by selective homolytic C(1)–N(8) bond cleavage, intersystem crossing, and cyclization of the zwitterionic intermediate on the ground potential energy surface. Subsequent photoinduced disrotatory stereospecific 4‐π‐electrocyclization of the 5,7‐bicyclic systems leads to 3D‐rich 5,5,4‐tricyclic products.

A monosubstituted benzene-1,2-diamine building block, N1-(3,5-bis(trifluoromethyl)benzyl)benzene-1,2-diamine, was prepared in two steps from commercially available 3,5-bis(trifluoromethyl)benzylamine and 1-fluoro-2-nitrobenzene, while the use of 3,5-bis(trifluoromethyl)aniline as the starting amine gave a triarylamine, N,N-bis(2-nitrophenyl)-3,5-bis(trifluoromethyl)aniline. The structures of the newly synthesized compounds were fully characterized.

A Cu(I)-photoredox-catalyzed trifluoromethylchlorosulfonylation reaction of terminal alkynes under visible light conditions was developed, giving rise to trifluoromethyl-substituted vinylsulfonyl chlorides, which can subsequently be coupled to a second alkyne under photocatalytic conditions. The transformation proceeds with high regio- and stereoselectivity and can be applied to aliphatic and aromatic alkynes with various functional groups. Trifluoromethyl-substituted divinyl sulfones prepared by this protocol can be readily used as synthetically valuable intermediates as demonstrated with various postmodification examples.

Ten novel bifunctional quaternary ammonium salt phase-transfer organocatalysts were synthesized in four steps from (+)-camphor-derived 1,3-diamines. These quaternary ammonium salts contained either (thio)urea or squaramide hydrogen bond donor groups in combination with either trifluoroacetate or iodide as the counteranion. Their organocatalytic activity was evaluated in electrophilic heterofunctionalizations of β-keto esters and in the Michael addition of a glycine Schiff base with methyl acrylate. α-Fluorination and chlorination of β-keto esters proceeded with full conversion and low enantioselectivities (up to 29% ee). Similarly, the Michael addition of a glycine Schiff base with methyl acrylate proceeded with full conversion and up to 11% ee. The new catalysts have been fully characterized; the stereochemistry at the C-2 chiral center was unambiguously determined.

Irradiation of mixtures of title diazonium salts and heteroarenes with green light (510 nm) in the presence of eosin Y disodium salt (EY-Na2) as a photocatalyst furnished the corresponding arylation products in 8-63% yields. The proposed photocatalytic cycle is analogous to that proposed previously for closely related photoredox C-H arylations with aryl diazonium salts as aryl radical sources. This method has a broad substrate scope and represents a metal-free alternative for the synthesis of 3-heteroaryl-substituted 4H-quinolizin-4-ones and azino- and azolo-fused pyrimidones with a bridgehead nitrogen atom.

The endo- and exo-N-heterocyclic carbene precursors based on camphor were prepared diastereoselectively in five synthetic steps starting from (1S)-(+)-ketopinic acid. The obtained N-heterocyclic carbene precursors were investigated in an asymmetric benzoin reaction. All new compounds were fully characterized, and the absolute configurations were determined via X-ray diffraction and NOESY measurements.

Organocatalyzed Michael addition of N-substituted tetramic acids to nitroalkene acceptors followed by O-alkylation gave polyfunctionalized tetramic acid (31 examples, 59-94% ee). The enantioselectivity of the product was influenced by the N-substituent of the substrate. Quantum chemical methods provided the mechanistic insights of the studied transformation. The preferred reaction pathway follows the model proposed by Papai et al. Single crystal structure confirmed the absolute configuration, which was in line with the ECD measured and calculated structure. Additionally, a comparative study of the alkylation of a selected tetramic and tetronic acid with trans-beta-nitrostyrene is disclosed. Follow-up amidations demonstrated the applicability of this class of compounds for the incorporation into both dipeptide and depsipeptide sequences.

Arylidene-Delta(2)-pyrrolin-4-ones undergo organocatalyzed annulation with malononitrile, furnishing dihydropyrano[3,2-b]pyrroles (18 examples, 0-77% ee in dichloromethane, 11-44% ee in methanol). The products could be enantiomerically enriched by trituration (11 examples, 95-99% ee). Enantioselectivity was dependent on the nature of the substrate and the conformation of the catalyst, which in turn was solvent-controlled. The reaction mechanism, which included two pseudo-enantiomeric organocatalyst conformations, was investigated by experimental and quantum chemical methods. The reaction mechanism consists of Michael addition reaction step followed by 6-exo-dig annulation, which was found to be the rate determining step. Additionally, it was identified that the preferred reaction pathway follows the model originally proposed by Papai et al.

A total of 24 novel organocatalysts based on (S)-quininamine as a chiral tertiary amine and on enaminone or 1,2-benzenediamine as hydrogen bond donors were synthesized. The enaminone-type catalysts were prepared by the transamination of N,N-dimethyl enaminones with (S)-quininamine (9 examples) and the 1,2-benzenediamine-type catalysts were prepared in 3 steps from (S)-quininamine and ortho-fluoronitrobenzene derivatives (15 examples). Their organocatalytic activity was evaluated in the Michael addition of acetylacetone to trans-β-nitrostyrene. Enantioselectivities of up to 72% ee were observed.

Nitroaromatic compounds (NACs) as important constituents of atmospheric humic-like substances (HULIS) and brown carbon (BrC) affect the Earth's climate and pose a serious environmental hazard. We investigated seasonal size-segregated NACs in aerosol samples from the urban background environment in Ljubljana, Slovenia. Total concentrations of twenty NACs in PM15.6 were on average from 0.51 ng m(-3) (summer) to 109 ng m? 3 (winter), and contributed the most to submicron aerosols (more than 74%). Besides 4-nitrocatechol (4NC) as the prevailing species, methylnitrocatechols (MNCs) and nitrophenols (NPs), we reported on some very rarely mentioned, but also on five novel NACs (i.e., 3H4NBA: 3-hydroxy-4-nitrobenzoic acid, 3MeO4NP: 3-methoxy-4nitrophenol, 4Et5NC: 4-ethyl-5-nitrocatechol, 3Et5NC: 3-ethyl-5-nitrocatechol and 3MeO5NC: 3-methoxy-5nitrocatechol). Concentrations of 3MeO5NC, 4Et5NC and 3Et5NC were enhanced during cold seasons, contributing up to 11% to total NAC in winter. In cold season, NAC size distributions were characterized with the peaks in the broader size range of 0.305-1.01 mu m (accumulation mode), with 4NC and alkyl-nitrocatechols ( n-ary sumation (M/Et) NC) as the most abundant, followed by 4-nitrosyringol, nitrophenols and nitroguaiacols. In spring, a pronounced peak of n-ary sumation (M/Et)NC was observed in the accumulation mode (0.305-0.56 mu m) as well as in the coarse one. A strong correlation of all NACs with n-ary sumation (M/Et)NC and levoglucosan indicates that primary emissions of wood burning were the most important source of NACs, but their secondary formation (e.g., aqueous-phase at higher ambient RH) in cold season could also be a significant one. In warmer season, NACs may be mostly derived from traffic-related aromatic VOCs. The contribution of NACs to the light absorption of the aqueous extracts was up to 10-times higher (contribution to Abs365 up to 31%) than their mass contributions to WSOC (up to 3%) of corresponding size-segregated aerosols, confirming that most of the identified NACs are strong BrC chromophores.

Herein, we report a one-pot site-selective dual metal catalyzed C-H diarylation reaction for the synthesis of multiarylated thiophene and furan derivatives in yields up to 92%. The regioselectivity of the developed methodology was achieved with the sequential use of two metal catalysts within a single vessel, starting with a Ru(II)-catalyzed C3 arylation assisted by an azine directing group, followed by a Pd(0)-catalyzed C-H functionalization on the C5-position of the five-membered heterocycle. Furthermore, the kinetic studies support that the position of the nitrogen atom within the azine moiety exhibits an evident effect on the efficiency of the ruthenium-catalyzed arylation step.

In the present study, we report the photochemical transformation of pyrazolo[1,2-a]pyrazolone substrates that reach an excited state upon irradiation with visible light to initiate the homolytic C-N bond cleavage process that yields the corresponding N1-substituted pyrazoles. Moreover, chemoselective heterolytic C-N bond cleavage is possible in the pyrazolo[1,2-a]pyrazole core in the presence of bromomalonate.

Phenols and phenol derivatives constitute important starting materials, synthetic intermediates, and functional moieties of a broad range of chemicals and materials. They represent large production products of benzene and benzene oxidation derivatives and are nowadays progressively available from biomass sources. In the last decades or so, there have been tremendous advances in the field of catalytic C–H bond functionalization, among which metal-catalyzed C–H bond functionalization of phenol derivatives plays a substantial role. In this review, the latest transition metal catalyzed C–H bond functionalizations of phenol derivatives are summarized. The presented methods are powerful tools for various C-H fucntionalziation reactions such as arylation, alkenylation, and acylation as well as annulation of phenol derivatives The presented C-H bond functionalziation of phenol derivatives were carried out in a highly step-economical mannerfrom readily available starting materials. Additionally, this review summarizes the main mechanistic aspects of the covered topic.

Arylidene-Δ2-pyrrolin-4-ones undergo organocatalyzed double spirocyclization with 3-isothiocianato oxindoles in a domino 1,4/1,2-addition sequence. The products contain three contiguous stereocenters (ee up to 98%, dr up to 99:1, 12 examples). The absolute configuration of the major diastereomer was determined by single crystal X-ray analysis. Along with heterocyclic Michael acceptors based on oxazolone, isoxazolone, thiazolidinone, pyrazolone, and pyrimidinedione, the reported results display the applicability of unsaturated Δ2-pyrrolin-4-ones (pyrrolones) for the organocatalyzed construction of 3D-rich pyrrolone-containing heterocycles.

Herein we report a study on the reactivity of C2‐quinoline‐substituted furan, thiophene and pyrrole derivatives in palladium‐catalyzed direct C–H arylation. The regioselectivity of the reaction was strongly influenced by site position of the attached five‐membered heterocycle thus giving rise to C3‐ and/or C5‐arylated products. Furthermore, the Hammett correlation performed on 5‐substituted‐8‐(furan‐2‐yl)quinolines indicates that a marginally positive charge is building up in the rate determining transition state and thus pointing towards the electrophilic metalation‐deprotonation reaction mechanism.