FeCl3-promoted formation of C–C bonds: synthesis of substituted quinolines from imines and electron-deficient alkynes

An efficient method for the synthesis of substituted quinolines is described. By FeCl₃-promoted C–C bond formation, 2,3-disubstituted and 2,3,4-trisubstituted quinolines were successfully synthesized from the reaction between imines and electron-deficient alkynes in good yields. The reaction can also be performed in a sequential three-component manner by using aromatic amines and aromatic aldehydes instead of the corresponding imines.     

Cobalt-catalyzed C–N,C–O,C–S bond formation: synthesis of heterocycles

In recent decades, a large number of reports related to the synthesis of N-, O- and S-containing heterocycles have appeared owing to a wide variety of their biological activity. Traditional approaches require expensive or highly specialized equipment or would be of limited use to the synthetic organic chemist due to their highly inconvenient approaches. New strategies have been developed for the preparation of heterocycles in the last decades. Metal and non-metal catalysts are used in organic reactions with high activity. These synthetic strategies are becoming important and highly rewarding protocols in organic synthesis. In this review article, the synthesis of heterocycles is presented with the application of cobalt metal as a catalyst. It describes the formation of different sized heterocyclic rings containing different heteroatoms.

     

Gold-catalyzed cascade C–C and C–N bond formation: synthesis of polysubstituted indolequinones and pyrroles

The combination of Ph₃PAuCl and AgOTf was proven to be an efficient catalyst for the cascade C–C and C–N bond formation reactions from enamines and bromoquinones or nitroolefins. This protocol affords a straightforward method for the synthesis of polysubstituted indolequinones and pyrroles in good yields.     

Recent strategic advances for the activation of benzylic C–H bonds for the formation of C–C bonds

Alkylarenes, obtained from abundant hydrocarbon feedstock sources, are an attractive starting material for the formation of complex molecular architectures. Conventional activation strategies of the relatively inert sp³-hybridized benzylic C–H bonds usually require relatively harsh conditions and are difficult to apply to the synthesis of fine chemicals. The present review describes recent strategic advances for the activation of benzylic C–H bonds for the catalytic formation of C–C bonds. In particular, two activation methods, i.e., strategies that generate benzylic radicals or benzyl anions, are discussed.     

Discovery of redox system enabling C–N–C bonds formation: Unprecedented Aza-Cannizzaro reaction

A novel reaction involving in situ redox conversion of glyoxylate esters to glycine is described. Simple starting materials and mild conditions for the synthesis of glycine derivatives probably indicate a pathway towards prebiotic chemistry. This proceeds analogous to Cannizzaro reaction involving ammonia therefore it can be termed as intramolecular Aza-Cannizzaro type reaction. This reaction is examined in detail with an aid of computational analysis to corroborate the proposed mechanism.     

Transition metal-catalyzed addition of C-, N- and O-nucleophiles to unactivated C–C multiple bonds

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Red yeast catalyzed animation of olefinic bonds and synthesis of optically pure S-amino acids

By using red yeast (Rhodotorula rubra AS 2.166) resting cells which possess the phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) activity as biocataiyst, enantiomerically pure S-3-(2-chloro-phenyl) alanine (2a) and S-3-(3-hydroxyphenyl) alanine (2d) have been synthesized from the corresponding 3-aryl substituted acrylic acid (1a and 1d) and ammonia.     

Gold-catalyzed simultaneous formation of C-C, C═O, and C-F bonds in the presence of Selectfluor: a synthesis of fluoroindenes from allene esters

An approach for the synthesis of fluorinated indene derivatives has been developed via a gold-catalyzed three-component tandem reaction between allene esters, Selectfluor, and water.     

Molybdenum trioxide catalyzed oxidative cross-dehydrogenative coupling of benzylic sp3 C–H bonds: synthesis of α-aminophosphonates under aerobic conditions

Molybdenum trioxide (MoO₃) catalyzed efficient oxidative cross-dehydrogenative-coupling (CDC) method for C–H functionalization of N-aryl tetrahydroisoquinolines has been explored. This user-friendly method of synthesizing α-aminophosphonates employs 1.1 equiv of dialkyl-H-phosphonate under aerobic condition. Formation of new C–P bonds from unfunctionalized starting materials under environmentally benign conditions provides an excellent avenue for the synthesis of biologically active α-aminophosphonates.     

Copper and zinc co-catalyzed synthesis of imidazoles via the activation of sp C–H and N–H bonds

An efficient and facile approach to synthesize imidazoles from amidines and arylketone via oxidative coupling of sp³ C–H bond and N–H bond is reported. This strategy exhibits high performance in terms of regioselectivity with moderate to high yields by using easily available materials, and provides an alternative method to synthesize multi-substituted imidazole skeletons.     

Challenges in C–C bond formation through direct transformations of sp2 C–H bonds

In the past several decades, organic chemists have made significant contributions to approach direct C–H transformations. However, limited substrate scope and reaction classifications, harsh condition, and the use of noble and toxic late transition-metal catalysts typically with high loadings clogged its applications. This article summarizes our recent efforts to explore new reaction types and develop new catalytic systems in this field, which may open a new channel to consider organic synthesis from easily available chemicals.     

Metal-free,PTSA catalyzed facile synthesis of β-ketoacetal from β-chlorocinnamaldehyde

A toluene solution of β-chlorocinnamaldehyde and dihydroxy alcohols in the catalytic presence of para-toluenesulphonic acid (PTSA) yield the β-ketoacetal in good to outstanding amount. The catalyst (PTSA), first selectively protect the aldehydic group to form the β-chloroacetal and the subsequent dechlorination by H₂O result the β-ketoacetal. Significant transformation was achieved with electron donating substituent attached at the para-position of cinnamaldehyde. The selective formation of β-keto-1,3-acetal was also obtained with a mixture of 1, 2- and 1, 3- diol. The present reaction consists of a metal-free, economical, robustly feasible, sizeable functional group tolerance and high yield properties. Moreover, the use of different dihydroxy alcohols made this process more benign and valuable towards the metal-free development of ketones. First, of its kind, a rare and unusual multitasking nature of PTSA is observed.     

Photochemical synthesis: Using light to build C–C bonds under mild conditions

A review of recent advancements in metal-free arylations via photogenerated triplet aryl cations and decatungstate anion ([W₁₀O₃₂]⁴⁻) photocatalyzed C–C bond formation is reported herein. These approaches are two examples of the great potentialities of photons as green activants in organic synthesis, allowing the functionalization of different chemical substrates under mild conditions (room temperature, aqueous solvents, absence of aggressive and unstable reactants and of expensive transition metal-based catalysts, and chance to use solar light as the energy source).     

P–C bond formation: synthesis of phosphino amino acids by palladium-catalysed cross-coupling

(4-Diethylphosphanyl)- and (4-diphenylphosphanyl)-derivatives of d- and l-phenylalanine have been synthesised using a palladium-catalysed cross-coupling giving the desired products in very high yields and without racemisation.     

Facile synthesis of 2-benzoxazoles via CuI/2,2'-bipyridine catalyzed intramolecular C–O coupling of 2-haloanilides

Development of newer methods for the synthesis of Benzoxazoles has of greater interest due to their wide range of biological activities and pharmaceutical importance. We herein report a facile and general method for the synthesis of 2-substituted Benzoxazoles via copper catalyzed intramolecular C–O cross-coupling of 2-haloanilides. A combination of CuI (5?mol%), 2,2'-bipyridine (10?mol%), Cs₂CO₃ (2 equiv.) in DMF solvent with 4?Å molecular sieves at 140?°C, illustrated the scope for tuning the reactivity of 2-haloanilides toward the selective formation of a series of 2-alkyl benzoxazole derivatives in moderate to good yields. This is the first systematic study using CuI/2,2'-Bipyridine as the catalytic system for the synthesis of 2-substituted Benzoxazoles. The outcome of the reaction was found to be significantly influenced by the aromatic and amide substituents of 2-haloanilides.     

A facile synthesis of α-aminophosphonates catalyzed by ytterbium perfluorooctanoate under solvent-free conditions

Three-component reactions of aldehydes, amines and diethyl phosphite are efficiently catalyzed by ytterbium perfluorooctanoate [Yb(PFO)₃] under solvent-free conditions, giving the corresponding α-aminophosphonates in good to excellent yields. The catalyst can be recovered and reused for several times without any significant loss of activity. Furthermore, a possible mechanism for this transformation is also presented.     

FeCl3 catalyzed sp C–H amination: synthesis of aminals with arylamines and amides

A simple and efficient amination of sp³ C–H bonds adjacent to a nitrogen atom in amides was introduced. The reaction was catalyzed by cheap and low toxic iron salt and used arylamines as nitrogen source. It provides a straightforward construction of acyclic aminals under mild conditions.     

RuCl₃·3H₂O catalyzed reactions: facile synthesis of bis(indolyl)methanes under mild conditions

RuCl?·3H?O was found to be an effective catalyst for reactions of indoles, 2-methylthiophene, and 2-methylfuran with aldehydes to afford the corresponding bis(indolyl)methanes, bis(thienyl)methanes, and bis(fur-2-yl)methanes in moderate to excellent yields. Experimental results indicated that mono(indolyl)methanol is not the reaction intermediate under these reaction conditions.     

A gram-scale synthesis of multi-substituted arenes via palladium catalyzed C–H halogenation

(6-Amino-2-chloro-3-fluorophenyl)methanol is prepared through both traditional methods and palladium catalyzed iterative C–H halogenation reactions.In comparison to traditional approach,the C–H functionalization strategy demonstrated a few advantages including milder reaction conditions higher yields,better selectivity and practicality,and high chemical diversity.