Visible Light Mediated Organophotoredox Catalyzed Synthesis of Tetraketones Using Tertiary Amines as Alkyl Synthons

Eosin Y catalyzed syntheses of bioactive tetraketones using cyclic-1,3-diketones and tertiary amines as alkyl synthons under 18 W blue LED have been accomplished. The condition is very mild that uses air as a green oxidant and avoids previously used harsh conditions like high temperature. Diverse arrays of tertiary amines first undergo reductive quenching of excited photocatalysts to form iminium ions that upon subsequent attack by cyclic-1,3-diketones give rise to tetraketones. This method is demonstrated with 31 examples with yields up to 76%. The feasibility of this reaction in the presence of eosin Y catalyst under a solar condition is also demonstrated with significant examples.

Amberlyst-A26-Mediated Corey-Chaykovsky Cyclopropanation of 9-Alkylidene-9H-fluorene under Continuous Process

Herein, we have developed a continuous-process for the direct cyclopropanation of various alkenes nonconjugated with carbonyl using trimethylsulfoxonium iodide as a methylene source via the Corey-Chaykovsky cyclopropanation reaction in the presence of Amberlyst-A26 as a heterogeneous base. Several 9-alkylidene-9H-fluorene derivatives successfully undergo Corey-Chaykovsky cyclopropanation to afford spiro[cyclopropane-1,9'-fluorene] in excellent yields under the continuous-process module. Furthermore, continuous process for the cyclopropanation of 3-benzylideneindolin-2-one derivatives using Amberlyst-A26 as a heterogeneous base has been described, which afford spiro[cyclopropane-1,3'-indolin]-2'-one derivatives.

Synthesis of Macrolactams from Macrolactones Using Ru-/Ir-Catalytic System under Neutral Conditions

Herein, we report the Ru-/Ir-catalyzed synthesis of valuable macrolactams from macrolactones and esters. The ring-opening of the macrolactones was efficaciously facilitated by the Ru catalyst to generate 32 amides in the first step. In the second step, intramolecular N-alkylative ring closure of amides with alcohols was succeeded by Ir catalyst to provide a series of 22 macrolactams and gave water as a byproduct. Moreover, this approach proceeded under neutral conditions and avoided the use of external additives.

Catalyst-Assisted Selective Vinylation and Methylallylation of a Quaternary Carbon Center Using tert-Butyl Acetate

The In(OTf)₃-catalyzed α-vinylation of various hydroxy-functionalized quaternary carbon centers using in situ generated isobutylene from tert-butyl acetate is presented as a novel synthetic methodology. Moreover, tert-butyl acetate is a nonflammable feed stock and is a readily available source for the in situ production of vinyl substituents, as demonstrated by the vinylation reaction with quaternary hydroxy/methoxy compounds. Moreover, an excellent selectivity for methylallylation over vinylation was obtained with Ni(OTf)₂ as a catalyst. In the case of peroxyoxindole, methylallyl-functionalized 1,4-benzoxazin-3-one derivatives were formed through the sequential rearrangement of peroxyoxindole followed by the nucleophilic attack by isobutylene. The detailed mechanism for this reaction and rationalization for the selectivity are provided using kinetics and density functional theory studies.

Continuous Flow Inter- and Intramolecular Macrolactonization under High Dilution Conditions

An efficient continuous flow process for the macrolactonization of seco acids and diacids using diols in the presence of Mukaiyama reagent (N-methyl-2-chloropyridinium iodide) has been developed for medium to large sized macrocyclic lactones. In comparison with other methods, the continuous flow process provided good to high yield in a short reaction time. By using this methodology, a wide range of macrocyclic lactones (11 compounds), dilactones (15 compounds), and tetralactone derivatives (2 compounds) with various ring sizes (12-26 atoms in the core) were synthesized in just 35 min of residence time. Advantageously, macrolactonization under the flow process is very elegant to handle the high dilution of reactants with a defined perfluoroalkoxy alkanes (PFA) tube reactor volume (7 mL).

Continuous-flow Fe-Zeolite catalyzed temperature directed synthesis of bioactive tetraketones and xanthenes using epoxide and cyclic-1,3-diketone via Meinwald rearrangement

An environmentally benign approach for the bioactive tetraketones using epoxides and cyclic-1,3-diketones in the presence of Fe-zeolite as a catalyst via Meinwald rearrangement has been developed under batch and continuous...

Lewis Acid-Catalyzed Chemodivergent and Regiospecific Reaction of Phenols with Quaternary Peroxyoxindoles

The indium-catalyzed regiospecific coupling of substituted phenol derivatives and quaternary peroxyoxindoles for the synthesis of C2 or C4 benzoxazin-3-one-substituted phenols via skeletal rearrangement is described. This reaction is demonstrated with 17 examples with good yields and diverse aryl substituents. In contrast to the indium-catalyzed reaction, the Cu(OTf)₂-catalyzed reaction of the phenol with quaternary peroxyoxindoles afforded C2 or C4 2-oxindole-substituted phenol derivatives. This diverse catalytic reaction generated various biologically important phenol-substituted 2-oxindole derivatives directly without any skeleton rearrangement and was demonstrated with 19 examples in high yield. The regiospecificity and the reaction pathways were explained with the support of density functional theory (DFT).

Continuous-Flow Direct Azidation of Alcohols and Peroxides for the Synthesis of Quinoxalinone, Benzooxazinone, and Triazole Derivatives

Continuous-flow reactors provide an ideal tool for the synthesis of potentially explosive but synthetically useful organic substances like organic azides due to their intrinsically small volume leading to very effective collision and highly controlled reaction conditions. Herein, we report the continuous-flow direct azidation of various alcohols by using TMSN₃ as an azide transfer reagent in the presence of Amberlyst-15 as a recyclable catalyst. Numerous 3-hydroxy-2-oxindoles effectively undergo azide transfer to afford azide-functionalized quaternary stereocenters in a continuous-flow module. Interestingly, peroxyoxindole undergoes sequential skeletal rearrangement to generate a carbocation followed by nucleophilic azidation to afford a library of substituted 2-azido-2H-benzo[b][1,4]oxazin-3(4H)-one derivatives under continuous flow. Furthermore, a continuous-flow Cu-catalyzed click reaction afforded triazole-functionalized deivatives. Next, reduction of azide in the presence of PPh₃ affords the amine derivatives in good yields. The continuous-flow application was extended further for the thermolytic skeletal rearrangement of 3-azide-2-oxindole for the synthesis of biologically important quinoxalin-2(1H)-ones without any reagents. Furthermore, this continuous-flow direct azidation reaction is scaled up to 6.144 g of azides with a turnover number of 9.24 under safer conditions.

Dehydrogenative Intramolecular Macrolactonization of Dihydroxy Compounds Using Ru-MACHO Catalyst

Herein, we have developed a new approach for the synthesis of 11 to 21-membered macrolactones via intramolecular dehydrogenative coupling of primary alcohols by using Ru-MACHO as a catalyst and Cs₂CO₃ as a base. This protocol generated 11-21-ring-sized macrocycles (26 derivatives), free from an external oxidant or an additive, eliminating stoichiometric reagents and producing only hydrogen as a byproduct.

Transition-Metal-Free Alkylative Aromatization of Tetralone Using Alcohol/Amino Alcohol towards the Synthesis of Bioactive Naphthol and Benzo[e/g]indole Derivatives

Herein, we report alkylative aromatization of tetralone for the synthesis of bioactive naphthols and benzo[e/g]indole derivatives using alcohols in the presence of NaOH via an aerobic oxidative cross-coupling protocol. This is a general and transition-metal-free method, which uses an inexpensive base, avoids inert conditions, and furnishes water and hydrogen peroxide as the byproducts. Moreover, this method demonstrated with wide substrate scope and obtained exclusive regioselectivity.

Ru-MACHO-Catalyzed Direct Inter/Intramolecular Macrocyclization of Alcohols and Ketones

Herein we describe a new approach for end-to-end cyclization to construct macrocycles through the inter/intramolecular dehydrogenative coupling of alcohols and ketones in the presence of a Ru-MACHO catalyst. This method is highly atom economical and sustainable and can be used for many substrates. Additionally, this method results in the generation of only water as the byproduct. Moreover, in this approach, high dilution of the reactants is crucial for cyclization and high-yield macrocycle synthesis.

Sequential Oxidative Fragmentation and Skeletal Rearrangement of Peroxides for the Synthesis of Quinazolinone Derivatives

For the first time, the sequential reaction of peroxyoxindole that involves base-promoted oxidative fragmentation to isocyanate formation and primary amine or amino alcohol accelerated skeletal rearrangement to synthesize exo-olefinic-substituted quinazolinone or oxazoloquinazolinone is reported. The advantages of this new reaction include a broad substrate scope and transition-metal-free and room-temperature conditions. The formation of the isocyanate as a key intermediate that accelerates oxidative skeletal rearrangement has been confirmed by trapping experiments and spectroscopic evidence.

Catalytic Acceptorless Dehydrogenation of Amino Alcohols and 2-Hydroxybenzyl Alcohols for Annulation Reaction under Neutral Conditions

A base-free and acceptorless Ru-catalyzed dehydrogenative approach has been developed for the synthesis of N-heterocycles by using 1,3-dicarbonyls and amino alcohols through a domino sequential enamine formation and intramolecular oxidative cyclization strategy. This unified approach is also applicable for the synthesis of O-heterocycles involving 2-hydroxybenzyl alcohol as a coupling reactant via consecutive C-alkylation and intramolecular cyclization steps. The present protocol is general for the synthesis of varieties of biologically important scaffolds, such as tetrahydro-4H-indol-4-one, 3,4-dihydroacridin-1(2H)-one, and tetrahydro-1H-xanthen-1-ones derivatives using a single catalytic system, viz. RuH₂CO(PPh₃)₃. Environmentally benign H₂O and H₂ are the only byproducts in this domino process. Moreover, RuH₂CO(PPh₃)₃-catalyzed C3-alkylation of tetrahydro-4H-indol-4-one using alcohol as a alkylating partner is also described in this report. For the first time, a solvent-free gram-scale reaction for the acceptorless dehydrogenative annulation has been demonstrated. A plausible mechanism for the Ru-catalyzed base-free and acceptorless dehydrogenative annulation of amino alcohols or 2-hydroxybenzyl alcohols has been provided with several experimental investigations and spectroscopic evidence.

Synthesis of Quaternary Spirooxindole 2H-Azirines under Batch and Continuous Flow Condition and Metal Assisted Umpolung Reactivity for the Ring-Opening Reaction

An efficient and new approach for the synthesis of spirooxindole 2H-azirines via intramolecular oxidative cyclization of 3-(amino(phenyl)methylene)-indolin-2-one derivatives in the presence of I₂ and Cs₂ CO₃ under batch/continuous flow is described. This method is mild and facile to synthesize a variety of spirooxindole 2H-azirines derivatives in gram-scale. Furthermore, we have synthesized spiroaziridine derivatives from spirooxindole 2H-azirines derivatives via addition of Grignard reagent. In addition, we discloses an metal assisted attack of Grignard nucleophile at N-centre rather than C- of the spirooxindole 2H-azirines, which concurrently underwent ring opening of transient aziridines to afford N-substituted Z-3-(aminophenyl)indolin-2-one. A plausible mechanism for azirination and ring-opening reaction is also presented.

Ligand-Free Ru-Catalyzed Direct sp3 C-H Alkylation of Fluorene Using Alcohols

The sp³ C-H alkylation of 9H-fluorene using alcohol and a Ru catalyst via the borrowing hydrogen concept has been described. This reaction was catalyzed by the [Ru(p-cymene)Cl₂]₂ complex (3 mol %) and exhibited a broad reaction scope with different alcohols, allowing primary and secondary alcohols to be employed as nonhazardous and greener alkylating agents with the formation of environmentally benign water as a byproduct. A variety of 9H-fluorene underwent selective and exclusive mono-C9-alkylation with primary alcohols in good to excellent isolated yield (26 examples, 50-92% yield), whereas this reaction with secondary alcohols in the absence of any external oxidants furnished the tetrasubstituted alkene as the major product. Furthermore, a base-mediated C-H hydroxylation of the synthesized 9H-fluorene derivatives afforded 9H-hydroxy-functionalized quaternary fluorene derivatives in excellent yield.

A continuous-flow approach for the multi-gram scale synthesis of C2-alkyl- or β-amino functionalized 1,3-dicarbonyl derivatives and ondansetron drug using 1,3-dicarbonyls

Continuous flow application has been developed for the gram-scale synthesis of C2-alkyl- or β-amino functionalized 1,3-dicarbonyl derivatives and ondansetron drug.

Transition-Metal-Free Addition Reaction for the Synthesis of 3-(Aminobenzylidene/aminoalkylidene)indolin-2-ones and Its Synthetic Applications

A novel and efficient transition-metal-free approach for the exclusive synthesis of Z-3-(aminobenzylidene/aminoalkylidene)indolin-2-ones in high yield from 2-oxindole and aryl/alkyl nitrile in the presence of LiOtBu and 2,2'-bipyridine system is described. In addition, we disclosed a new approach towards the metal-free fluorination using selectfluor and the C═C bond cleavage using CuI and environmentally benign O₂.

MnO2 @Fe3 O4 Magnetic Nanoparticles as Efficient and Recyclable Heterogeneous Catalyst for Benzylic sp3 C-H Oxidation

Herein, we report a highly chemoselective and efficient heterogeneous MnO₂ @Fe₃ O₄ MNP catalyst for the oxidation of benzylic sp³ C-H group of ethers using TBHP as a green oxidant to afford ester derivatives in high yield under batch/continuous flow module. This catalyst was also effective for the benzylic sp³ C-H group of methylene derivatives to furnish the ketone in high yield which can be easily integrated into continuous flow condition for scale up. The catalyst is fully characterized by spectroscopic techniques and it was found that 0.424 % MnO₂ @Fe₃ O₄ catalyzes the reaction; the magnetic nanoparticles of this catalyst could be easily recovered from the reaction mixture. The recovered catalyst was recycled for twelve cycles without any loss of the catalytic activity. The advantages of MnO₂ @Fe₃ O₄ MNP are its catalytic activity, easy preparation, recovery, and recyclability, gram scale synthesis with a TOF of up to 14.93 h^-1 and low metal leaching during the reaction.

Reversible chemoselective transetherification of vinylogous esters using Fe-catalyst under additive free conditions

An additive/Brønsted acid/base free, highly efficient and chemoselective transetherification of electron deficient vinylogous esters and water mediated de-alkylation using an earth-abundant Fe-catalyst under very mild reaction conditions is described. This reaction is highly selective to primary alcohols over secondary alcohols, has good functional group tolerance, is scalable to gram scale and a purification free sequential transetherification in a continuous flow mode is demonstrated.

Peroxidation of 2-oxindole and barbituric acid derivatives under batch and continuous flow using an eco-friendly ethyl acetate solvent

We have demonstrated the magnetically retrievable Fe(OH)₃Fe₃O₄catalyzed C–H peroxidation of 2-oxindole and barbituric acid derivatives under batch and continuous flow process for the first time.

Ru-Catalyzed dehydrogenative synthesis of antimalarial arylidene oxindoles

Ru(ii)-NHC catalyzes α-olefination of 2-oxindoles using diaryl methanols in the absence of an acceptor. A wide array of symmetrical and unsymmetrical diaryl methanols undergoes dehydrogenative coupling with 2-oxindole selectively to generate various substituted 3-(diphenylmethylene)indolin-2-one derivatives in good yields and produces environmentally benign by-products, H2 and H2O. This methodology was successfully applied for the synthesis of a bioactive drug i.e. TAS-301. The biological activities of the synthesized 3-(diphenylmethylene)indolin-2-one derivatives were screened against the Plasmodium falciparum parasite and found to exhibit a significant activity with IC50 = 2.24 μM.

Ru-NHC Catalyzed Domino Reaction of Carbonyl Compounds and Alcohols: A Short Synthesis of Donaxaridine

Direct α-alkylation of amides and the synthesis of C3-alkylated 3-hydroxyindolin-2-one/2-substituted-2-hydroxy-3,4-dihydronaphthalen-1(2H)-one derivatives from 2-oxindole/1-teralone were reported using primary alcohols in the presence of Ru-NHC catalyst in a one pot condition under the borrowing hydrogen method. In the case of inert conditions, 2-oxindole/1-teralone exclusively forms the C3-alkylated product. Whereas, allowing this reaction mixture to occur under an air atmosphere predominantly forms C3-alkylated 3-hydroxyindolin-2-one via domino C-H alkylation and aerobic C-H hydroxylation. This Ru-NHC catalyst is easily accessible, air stable, and phosphine free. Using this method, synthesis of 2-oxindole based natural products such as Donaxaridine was accomplished.

Ruthenium-catalyzed direct α-alkylation of amides using alcohols

The Ru-catalyzed (0.1 mol%) direct α-alkylation of amides using alcohols is reported.

Benzimidazolin-2-ylidene N-heterocyclic carbene complexes of ruthenium as a simple catalyst for the N-alkylation of amines using alcohols and diols

Simple non-chelating ruthenium benzimidazolin-2-ylidene complexes as efficient N-alkylation catalysts using alcohols and diols following a hydrogen borrowing strategy.

Synthesis of amides from esters and amines with liberation of H2 under neutral conditions

Efficient synthesis of amides directly from esters and amines is achieved under mild, neutral conditions with the liberation of molecular hydrogen. Both primary and secondary amines can be utilized. This unprecedented, general, environmentally benign reaction is homogeneously catalyzed under neutral conditions by a dearomatized ruthenium-pincer PNN complex and proceeds in toluene under an inert atmosphere with a high turnover number (up to 1000). PNP analogues do not catalyze this transformation, underlining the crucial importance of the amine arm of the pincer ligand. A mechanism is proposed involving metal-ligand cooperation via aromatization-dearomatization of the pyridine moiety and hemilability of the amine arm.

Direct hydrogenation of amides to alcohols and amines under mild conditions

The selective, direct hydrogenation of amides to the corresponding alcohols and amines with cleavage of the C-N bond was discovered. The expected products of C-O cleavage are not formed (except as traces in the case of anilides). The reaction proceeds under mild pressure and neutral, homogeneous conditions using a dearomatized, bipyridyl-based PNN Ru(II) pincer complex as a catalyst. The postulated mechanism involves metal-ligand cooperation by aromatization-dearomatization of the heteroaromatic pincer core and does not involve hydrolytic cleavage of the amide. The simplicity, generality, and efficiency of this environmentally benign process make it attractive for the direct transformations of amides to alcohols and amines in good to excellent yields.