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.

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.

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.

Herein, we report a highly chemoselective and efficient heterogeneous MnO2@Fe3O4 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@Fe3O4 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@Fe3O4 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.

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...

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 TMSN 3 as an azide transfer reagent in the presence of Amberlyst-15 as a recyclable catalyst. Numerous 3hydroxy-2-oxindoles effectively undergo azide transfer to afford azidefunctionalized 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 PPh 3 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.

The In(OTf)3-catalyzed α-vinylation of various hydroxy functionalized quaternary carbon centre by using isobutylene generated in situ from tert-butyl acetate is presented as first synthetic methodology. Moreover, tert-butyl acetate is non-flammable feedstock and is a readily available source for the in-situ production of vinyl substituents, demonstrated vinylation reaction with quaternary hydroxy/methoxy compounds. Moreover, an excellent selectivity for the methylallylation over the vinylation was obtained with Ni(OTf)2. In case of peroxyoxindole, methylallyl functionalized 1,4-benzoxazin-3-one derivatives were formed through the sequential rearrangement of peroxyoxindole and the nucleophilic attack by isobutylene. The detailed mechanism for this reaction has been provided based on the preliminary experiments and kinetics studies.

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.