Solvent Dependent Competitive Mechanisms for the Ugi Multicomponent Reaction: A Joint Theoretical and Experimental Study in the α-Acyl Aminocarboxamides vs α-Amino Amidines Formation

A synthetic protocol for the preparation of α-acyl aminocarboxamides and α-amino amidines is proposed. The selectivity toward each of these two possible products was tuned by simple modifications of the reaction conditions. A broad scope is presented, allowing access to the desired products in up to 87% (Ugi adduct) and 93% (α-amino amidine). Theoretical calculations were carried out, and the analysis led to the proposal of a new mechanistic pathway for the Ugi reaction, in which methanol acts not only as the solvent but also as a reagent. High-resolution (tandem) mass spectrometry experiments allowed the detection and characterization of the key intermediate associated with this new and alternative reaction pathway, thus supporting the theoretical proposal.

A water-soluble fluorescent sensor for the quick discrimination of H2O and D2O by notable signal outputs and the real-time monitoring of food spoilage in a non-contact mode

Due to the very similar chemical and physical properties, D2O and H2O cannot be discriminated easily by convenient and cost-effective ways.

An Operationally Simple and Efficient Synthesis of 7-Benzylidene-substitutedphenyl- 3,3a,4,5,6,7-hexahydro-2H-indazole by Grinding Method

BACKGROUND

An eco-friendly, operationally simple and efficient reaction is shown between various 2,6-bis-(substituted-benzylidene)-cyclohexanones and differently substituted hydrazine in the presence of acetic acid.

METHODS

The reaction between various 2,6-bis-(substituted-benzylidene)-cyclohexanones and differently substituted hydrazine in the presence of acetic acid afforded 7-Benzylidene-substituted-phenyl-3,3a,4,5,6,7- hexahydro-2H-indazole in 74 to 92 % yield in short reaction time using the grindstone technique.

RESULTS AND DISCUSSION

The notable advantages of this method include mild synthetic conditions, weak acid catalysis, and non-hazardous solvent which make this method environmentally safer.

CONCLUSION

In conclusion, we have developed an efficient, simple and eco-friendly method for the synthesis of 7-Benzylidene-substituted-phenyl-3,3a,4,5,6,7-hexahydro-2H-indazole by grinding technique. The notable benefits of this method are waste minimization, no organic solvent required, simple procedure, easy work-up, and clean reaction profile.

Regioselective C3-H Trifluoromethylation of 2 H-Indazole under Transition-Metal-Free Photoredox Catalysis

Trifluoromethyl-substituted heteroarenes are biologically active compounds and useful building blocks. In this sequence, we have developed a visible-light-promoted regioselective C3-H trifluoromethylation of 2 H-indazole under metal-free conditions, which proceeds via a radical mechanism. The combination of photocatalysis and hypervalent iodine reagent provides a practical approach to a library of trifluoromethylated indazoles in 35-83% yields.

Post-Ugi Cyclization for the Construction of Diverse Heterocyclic Compounds: Recent Updates

Multicomponent reactions (MCRs) have proved as a valuable tool for organic and medicinal chemist because of their ability to introduce a large degree of chemical diversity in the product in a single step and with high atom economy. One of the dominant MCRs is the Ugi reaction, which involves the condensation of an aldehyde (or ketone), an amine, an isonitrile, and a carboxylic acid to afford an α-acylamino carboxamide adduct. The desired Ugi-adducts may be constructed by careful selection of the building blocks, opening the door for desired post-Ugi modifications. In recent times, the post-Ugi transformation has proved an important synthetic protocol to provide a variety of heterocyclic compounds with diverse biological properties. In this review, we have discussed the significant advancements reported in the recent literature with the emphasis to highlight the concepts and synthetic applications of the derived products along with critical mechanistic aspects.

A General One-Pot Synthesis of 2H-Indazoles Using an Organophosphorus-Silane System

A simple and direct approach for the regioselective construction of the privileged 2H-indazole scaffold is described. The developed one-pot strategy involves phospholene-mediated N-N bond formation to access 2H-indazoles. The amount of organophosphorus reagent was minimized by recycling the phospholene oxide with organosilane reductants. Starting from functionalized 2-nitrobenzaldehydes and primary amines, a mild reductive cyclization, involving the use of commercially available phospholene oxide and silanes, delivered a wide variety of substituted 2H-indazoles in good to excellent yields.

Iron promoted C3–H nitration of 2H-indazole: direct access to 3-nitro-2H-indazoles

An efficient C3–H functionalization of indazole has been demonstrated. Notably, this method involves chelation-free radical C–H nitration on 2H-indazole. The radical mechanism was confirmed by control experiments and quantum chemical calculations. The synthetic utility has been proven by the synthesis of bio-relevant benzimidazoindazoles via reductive cyclization.

Silica gel mediated oxidative C–O coupling of β-dicarbonyl compounds with malonyl peroxides in solvent-free conditions

For the first time silica gel was observed to activate peroxides in oxidative coupling reactions. Here we report silica gel mediated oxidative C–O coupling of β-dicarbonyl compounds with cyclic diacyl peroxides affording α-acyloxy derivatives with 100% atom efficiency. The highest yields of coupling products were achieved in solvent free conditions. C–O coupling products were prepared in yields up to 86%.

Organophosphorus-mediated N-N bond formation: facile access to 3-amino-2H-indazoles

A convenient and efficient strategy has been devised to access 3-amino-2H-indazole derivatives in two steps from readily available starting materials. The conversion of 2-nitrobenzonitriles to substituted benzamidines followed by an organophosphorus-mediated reductive cyclization and a subsequent N-N bond formation afforded 3-amino-2H-indazoles in good to excellent yields.

A metal-free cyclic iminium induced one-pot double annulation cascade: access to dihydroisoquinolinium (DHIQ) salts

A reactive cyclic iminium induced one-pot Groebke–Blackburn–Bienayme (GBB) double annulation cascade (DAC) for the synthesis of skeletally diverse DHIQ salts has been described. The key features of this protocol are solvent-free, robust method, clean reaction profile and operational simplicity.

Synthesis of novel imidazole-based triheterocycles via a domino Ugi/Michael reaction and silver-catalyzed heteroannulation

An efficient and diversity-oriented synthetic strategy for novel triheterocyclic imidazo-pyrrolo-pyrazine/diazepine/diazocine derivatives is elaborated.

Hypervalent iodine(iii)-promoted N-incorporation into N-aryl vinylogous carbamates to quinoxaline diesters: access to 1,4,5,8-tetraazaphenanthrene

An oxidative N-incorporation strategy for synthesis of quinoxaline diesters under metal-free and mild reaction conditions is described via the formation of two C(sp²)–N bonds utilizing NaN₃ as the cheap N-atom source.

BF3·OEt2 mediated metal-free one-pot sequential multiple annulation cascade (SMAC) synthesis of complex and diverse tetrahydroisoquinoline fused hybrid molecules

A highly efficient and distinct BF₃·OEt₂ mediated one-pot metal-free sequential multiple annulation cascade (SMAC) protocol for the synthesis of complex and diverse THIQ fused hybrid molecules has been presented.

A new route for the synthesis of highly substituted 4-aminoquinoline drug like molecules via aza hetero–Diels–Alder reaction

A new route has been developed for the synthesis of 4-aminoquinoline drug like moleculesviaaza hetero–Diels–Alder reaction starting from 2H-indazole as a diene for the first time.

Silica gel-promoted practical synthesis of oxindole–nitrones from diazooxindoles and nitrosoarenes under solvent-free conditions

A practical and efficient method for the synthesis of oxindole–nitrones from diazooxindoles and nitrosoarenes promoted by silica gel was developed.