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The chemistry of boron compounds has been profoundly investigated in the last decades, leading to ubiquity in many synthetic applications as well as biologically active molecules. Since the advent of photoredox catalysis, an upsurge in the discovery of suitable radical precursors has been witnessed, and boron is becoming a protagonist in this field. Despite many studies focused on trifluoroborates, the use of boronic acids and esters have received much less attention in this regard. Because of their high oxidation potential, the development of methods to enable their involvement in photocatalyzed reactions is only recent. Nonetheless, this review summarizes novel strategies developed to unlock their role as radical precursors in photochemical reactions and discloses the potential that boronic acids and esters own, when their intrinsic chemical properties are exploited. [ABSTRACT FROM AUTHOR]

Graphical abstract This review highlights the recent advances towards post-MCR transformations towards complex (poly)heterocycles based on gold-catalyzed key steps. Post multicomponent reaction (MCR) transformations are one of the most successful methods leading to high structural diversity and molecular complexity. A well-known MCR, the Ugi reaction typically affords a linear peptide backbone, enabling post-Ugi transformations as an elegant solution to rigidify the Ugi adduct into more drug-like species. Not surprisingly, the development of such transformations leading to new structural frameworks has expanded rapidly over the last few years. These reactions have reached an impressive level of performance and versatility, particularly in amalgamation with gold catalysis. This review outlines the developments achieved in the past decade, highlighting the modifications that are performed in a sequential or domino fashion with emphasis on major concepts, synthetic applications of the derived products as well as mechanistic aspects. [ABSTRACT FROM AUTHOR]

We report herein an efficient gold(I)-catalyzed post-Ugi domino dearomatization/ ipso-cyclization/Michael sequence that enables access to libraries of diverse (hetero)arene-annulated tricyclic heterocycles. This process affords novel complex polycyclic scaffolds in moderate to good yields from readily available acyclic precursors with excellent chemo-, regio-, and diastereoselectivity. The power of this strategy has been demonstrated by the rapid synthesis of 40 highly functionalized polyheterocycles bearing indole, pyrrole, (benzo)furan, (benzo)thiophene, pyrazole, and electron-rich arene groups in two operational steps. [ABSTRACT FROM AUTHOR]

A one-pot procedure involving a four-component Ugi reaction followed by an intramolecular Diels-Alder reaction/HCl elimination cascade has been developed to provide rapid access to the isoindolinone framework in a diversity-oriented fashion. The scope of the process has been investigated with respect to all four components, and a comparison between the one-pot and sequential approaches is given. The possibility of a late-stage one-pot functionalization through Suzuki coupling has been explored. [ABSTRACT FROM AUTHOR]

A one-pot sequential A3-coupling-azidation-cyclisation approach leading to potentially biologically active diazepine analogues has been developed. The implementation of the A3-coupling reaction ensures diversity. Attention is given to this so far rarely studied structural motif of fused heterocyclic diazepines. [ABSTRACT FROM AUTHOR]

We report the utilization of a novel catalyst for cycloisomerizations. The novel catalyst system contains gold nanoparticles supported on Al-SBA15, which was prepared by the ball-milling process. We developed a greener methodology for synthesizing spiroindolines under heterogeneous conditions, using this novel class of supported gold nanoparticles in combination with microwave irradiation. The catalyst is highly reusable and selective. Cycloisomerization reaction yields ranged from good to excellent leading to the formation of two novel classes of six- and seven-membered heterocycles, which have been unprecedented so far. The selectivity of the catalyst towards the desired products is high and the reaction can be performed in ethanol as the solvent. A one-pot cascade reaction could be established commencing with the Ugi-reaction to ensure diversity. [ABSTRACT FROM AUTHOR]

The Ugi-4CR is by far one of the most successful multicomponent reactions leading to high structural diversity and molecular complexity. However, the reaction mostly affords a linear peptide backbone, enabling post-Ugi transformations as the only solution to rigidify the Ugi-adduct into more drug like species. Not surprisingly, the development of these transformations, leading to new structural frameworks, has expanded rapidly over the last few years. As expected, palladium-catalyzed reactions have received the foremost attention, yet other metals, particularly gold complexes, are fast catching up. This tutorial review outlines the developments achieved in the past decade, highlighting the modifications that are performed in a sequential or domino fashion with emphasis on major concepts, synthetic applications of the derived products as well as mechanistic aspects. [ABSTRACT FROM AUTHOR]

A cascade transformation involving the Ugi reaction followed by 5-endo-dig carbocyclization and retro-Claisen fragmentation providing access to a 1H-pyrrol-2(5H)-one core is described. The operating protocol is very similar to the typical Ugi reaction settings, while the overall outcome results from the application of a 3-substituted propiolic acid and a phenylglyoxal as acid and aldehyde components, respectively. The utility of process is demonstrated through the synthesis of a small library of 5-oxo-2,5-dihydro-1H-pyrrole-2-carboxamides. [ABSTRACT FROM AUTHOR]

A highly efficient approach for the regioselective construction of fused nine-membered rings (diazoninone framework) was developed by employing sequential Ugi and gold-catalyzed intramolecular hydroarylation reactions. The scope of this intramolecular cyclization has been demonstrated. [ABSTRACT FROM AUTHOR]

A post-Ugi late-transition-metal-catalyzed intramolecular hydroarylation approach opens a new gateway for the synthesis of diversely substituted pyrrolopyridinones, pyrroloazepinones thiophenoazepinones, azepinoindoles, and azepinobenzothiophenes applying mild reaction conditions. A detailed investigation of the scope of this strategy is discussed. [ABSTRACT FROM AUTHOR]

An efficient one-pot protocol for the synthesis of isoquinolinium- 2-yl amides starting from readily available hydrazides and 2-alkynylbenzaldehydes is described. The key step of the protocol is a silver(I)-catalyzed ring-closure of N'-(2-alkynylbenzylidene) hydrazides that are generated in situ. Isoquinolinium-2-yl amides derived from tert-butoxycarbonyl hydrazide could be further deprotected, delivering 2-aminoisoquinolinium trifluoroacetates. [ABSTRACT FROM AUTHOR]

Among the fundamental transformations in the field of synthetic organic chemistry, transition-metal-catalyzed reactions provide some of the most attractive methodologies for the formation of C–C and C-heteroatom bonds. As a result, the application of these reactions has increased tremendously during the past decades and cross-coupling reactions became a standard tool for synthetic organic chemists. Furthermore, a tremendous upsurge in the development of new catalysts and ligands, as well as an increased understanding of the mechanisms, has contributed substantially to recent advances in the field. Traditionally, organic reactions are carried out by conductive heating with an external heat source (for example, an oil bath). However, the application of microwave irradiation is a steadily gaining field as an alternative heating mode since its dawn at the end of the last century. This tutorial review focuses on some of the recent developments in the field of cross-coupling reactions assisted by microwave irradiation. [ABSTRACT FROM AUTHOR]

Abstract: Microwave irradiation was applied in the racemization and dynamic kinetic resolution of primary benzylic amines. Racemization reactions catalyzed by 5% Pd/BaSO4 and 5% Pd/CaCO3 were faster and more selective when performed under microwave conditions. The use of microwave irradiation stopped the formation of side products, such as secondary amines and ethylbenzene. This was correlated with the selective heating of the metal sites under microwave heating. The influence of the microwave irradiation also was checked in the kinetic resolution; no influence on the activity and enantioselectivity of the immobilized Candida Antarctica Lipase B (Novozym 435) was observed when both conventional and microwave heating were compared. The racemization catalysts were combined in one pot with the biocatalyst Novozym 435 to perform the dynamic kinetic resolution of benzylic amines under microwave irradiation. High yields (up to 88%) of enantiopure amides were obtained in less than 1 h when microwave irradiation was applied. [Copyright &y& Elsevier]

1-(p-Methoxyphenyl)tetrazolyl-substituted 6,7-dimethoxy(6,7-methylenedioxy)-1,2,3,4-tetrahydroisoquinolines formed tetrazolyl-substituted azocines in high yields by using activated alkynes. Unsubstituted at 6,7,8-aromatic fragment 1-tetrazolylisoquinoline interacted in several pathways forming tetrazolyl-substituted azocines, 1-tetrazolyl-1-R-vinylisoquinolines and 3-azaspiro[5.5]undeca-1,7,9-triene. [ABSTRACT FROM AUTHOR]

We describe here an efficient method to synthesize 1-aryl-15 H -dibenzo[ d , h ][1,2,3]triazolo[1,5- a ][1,3,6]triazonines by copper-catalyzed intramolecular Ullmann cross-coupling reaction. Reactions between a range of 5-iodo-1,2,3-triazoyl benzaldehydes and substituted diaminobenzenes in the presence of a catalytic amount of CuI (5 mol %) in DMSO at 100 °C under microwave irradiation have proven to be an efficient way to access new fused 1,2,3-triazolo-1,3,6-triazonines in good to excellent yields. [ABSTRACT FROM AUTHOR]

A three-component reaction of a 2-aminoazine, a 2-oxoaldehyde, and a cyclic 1,3-dicarbonyl compound providing access toward a novel class of imidazo[1,2-a]azine derivatives was developed and studied. The scope of the process was thoroughly explored under three different reaction conditions resulting in the generation of a small library of title compounds and highlighting the possibility of case-specific approach. [ABSTRACT FROM AUTHOR]

An unprecedented microwave-assisted multicomponent strategy has been elaborated for the fast, efficient, and diastereoselective generation of the dibenzo[c,e]azepinone scaffold. The generated compounds were evaluated for their bioactivity. [ABSTRACT FROM AUTHOR]

Abstract: A Biginelli-like three-component condensation using 3-amino-1,2,4-triazole as urea component resulted in an unexpected alternative direction of the tetrahydropyrimidine ring formation. [Copyright &y& Elsevier]

Abstract: Catalyst-free alcoholytic deprotection of borane-protected phosphorus compounds offers a smooth, efficient, and clean alternative to existing deprotection methods. In this paper we report our results on the general applicability of deprotecting phosphane- and phosphite-borane adducts by means of simple alcoholysis without the use of molecular sieves as a catalyst. Phosphane-boranes bearing at least one aromatic substituent are readily deprotected in high yields. Borane complexes of trialkylphosphanes or phosphites, however, cannot be deprotected in this way. The main merit of our method is its simplicity: apart from evaporation of the solvent, no further work-up or purification is needed. [Copyright &y& Elsevier]

Abstract: A continuous flow procedure has been elaborated for the copper(II)-mediated N- and O-arylation of a range of compounds with arylboronic acids using a commercial microreactor setup. The compounds could be continuously generated in good yields paving the way for efficient scalability. [Copyright &y& Elsevier]

A novel and convenient procedure for the synthesis of asymmetrically tri- and tetrasubstituted pyrazines starting from para-methoxybenzyl-protected 3,5-dichloro-2(1H)-pyrazinones was elaborated. The key step is the conversion of the intermediate para-methoxybenzyl-protected thiopyrazinone upon treatment with MeI/I2, into a pyrazine, rendering the chlorine in the C5-position susceptible to substitution. This approach entails the orthogonal introduction of the four substituents of the pyrazine scaffold. The application of microwave irradiation during different steps of the sequence has been shown to be highly valuable for speeding up reactions. [ABSTRACT FROM AUTHOR]

The article presents chemical equations related to the article "The Application of Multicomponent Ugi and Passerini Reactions for the One-Pot Synthesis of Pyrrolones and Butenolides" by A. A. Nechaev and colleagues, published in the Synthesis journal in 2016.

Review: 50 refs. [ABSTRACT FROM AUTHOR]

The simple procedure is carried out with equimolar amounts of substrates and affords a series of highly functionalized pyrrole structures. [ABSTRACT FROM AUTHOR]

The Ugi four-component reaction of 2-pyrrole aldehydes and analogous indole and benzothiophene aldehydes with primary amines, isonitriles, and alkynoic acids offers the expected adducts (V), (XI), and (XIV) which can be readily used for the synthesis of various fused pyridones and azepinones. [ABSTRACT FROM AUTHOR]

An efficient intramolecular hydroarylation reaction to the corresponding title heterocycles under mild reaction conditions is developed. [ABSTRACT FROM AUTHOR]

A novel microwave-assisted protocol is developed to give the title products in varying yields depending on the substitution pattern of the substrates. [ABSTRACT FROM AUTHOR]