A photocatalyst-free visible-light-mediated solvent-switchable route to stilbenes/vinyl sulfones from ß-nitrostyrenes and arylazo sulfones.

Photocatalyst-free visible-light-mediated reactions, based on the presence of a visible-light-absorbing functional group in the starting material itself in order to exclude the often costly, hazardous, degradable and difficult to remove or recover photoredox catalysts, have been gaining momentum recently. We have employed this approach to develop a denitrative photocatalyst-free visible-light-mediated protocol for the arylation/sulfonylation of ß-nitrostyrenes employing arylazo sulfones (bench-stable photolabile compounds) in a switchable solvent-controlled manner. Arylazo sulfones served as the aryl and sulfonyl radical precursors under blue LED irradiation for the synthesis of trans-stilbenes and (E)-vinyl sulfones in CH3CN and dioxane/H2O 2 : 1, respectively. The absence of any metal, photocatalyst and additive; excellent selectivity (E-stereochemistry) and solvent-switchability; and the use of visible light and ambient temperature are the prime assets of the developed method. Moreover, we report the first photocatalyst-free visible light-driven route to synthesize stilbenes and vinyl sulfones from readily available ß-nitrostyrenes.

Organic photoredox catalysis enabled cross-coupling of arenediazonium and sulfinate salts: synthesis of (un)symmetrical diaryl/alkyl aryl sulfones.

We disclose herein the first transition-metal- and external oxidant/reductant-free visible-light-mediated synthesis of (un)symmetrical diaryl/alkyl aryl sulfones from arenediazonium tetrafluoroborates and sodium sulfinates using eosin Y as an organic photoredox catalyst. The utilization of visible light as an inexpensive and ecosustainable energy source, operational simplicity, ambient temperature and clean reaction in aqueous acetonitrile are the salient features of the developed protocol. The desired sulfones were also synthesized via a one-pot, two-step process directly from anilines and sulfinate salts in good to excellent yields.

N-Hydroxyphthalimide: a new photoredox catalyst for [4+1] radical cyclization of N-methylanilines with isocyanides.

The first utilization of N-hydroxyphthalimide (NHPI) as an organophotoredox catalyst is demonstrated by the [4+1] radical cyclization reaction of N-methylanilines with isocyanides. The protocol offers an operationally simple one-pot synthesis of 3-iminodihydroindoles at room temperature.

Direct construction of 2-alkylbenzo-1,3-azoles via C-H activation of alkanes for C-C and C-X (X = O, S) bond formation.

Copper catalyzed straightforward synthesis of 2-alkylbenzoxa(thia)azoles from aryl isocyanates/isothiocyanates and simple alkanes is reported. The protocol utilizes ditertiary butyl peroxide (DTBP) as a radical initiator and involves sequential formation of C-C and C-X (X = O, S) bonds followed by aromatization in a one-pot procedure.

Aerobic oxysulfonylation of alkenes using thiophenols: an efficient one-pot route to ß-ketosulfones.

We have developed a highly efficient synthetic route to ß-ketosulfones via AgNO3 catalyzed oxysulfonylation of alkenes using thiophenols in the presence of air (O2) and K2S2O8 as eco-friendly oxidants. Thiophenols have been used as sulfonylation precursors for the first time in a dioxygen activation based radical process. Moreover, the protocol also offers a new and convenient method for the synthesis of ß-hydroxysulfides at room temperature without the use of any initiator.

An easy access to fluoroalkanes by deoxygenative hydrofluorination of carbonyl compounds via their tosylhydrazones.

An efficient and operationally simple synthesis of fluoroalkanes by deoxygenative hydrofluorination of carbonyl compounds via their tosylhydrazone surrogates is reported. The reaction can be carried out in a one-pot procedure directly from carbonyl compounds.

Unprecedented dithiolation of enals via their NHC-catalysed umpolung reaction with organic disulfides.

A novel one-pot N-heterocyclic carbene (NHC)-catalysed dithiolation of α,ß-unsaturated aldehydes (enals) with organic disulfides is reported. The protocol involves homoenolate reactivity of enals, where the homoenolate attacks on the disulfide as a d(3) nucleophile followed by thioesterification to afford ß-aryl/alkylsulfanyl thioesters with complete atom economy.

NHC-catalysed diastereoselective synthesis of multifunctionalised piperidines via cascade reaction of enals with azalactones.

NHC-catalysed azalactone ring-opening and piperidine ring-closing cascade with α,ß-unsaturated aldehydes (enals) in a one-pot operation is reported. The present reaction cascade offers a convenient method for a highly diastereoselective synthesis of multifunctionalised piperidines in excellent yields under mild conditions.

Strategic applications of Baylis-Hillman adducts to general syntheses of 3-nitroazetidines.

A novel one-pot highly diastereoselective synthesis of substituted 3-nitroazetidines via an anionic domino process is described. The synthesis involves a high yielding annulation of Baylis-Hillman alcohols and their aldehydes with either N-aryl/tosylphosphoramidates or N-aryl/tosylphosphoramidates in combination with a task-specific ionic liquid [bmim][X-Y] to afford the corresponding 1,2,3-tri- and 1,2,3,4-tetrasubstituted azetidines, respectively. Plausible mechanisms for the formation of various 3-nitroazetidines have been suggested.

Cyclopropenium ion catalysed Beckmann rearrangement.

1-Chloro-2,3-diphenylcyclopropenium ion was found to be a very efficient organocatalyst (3 mol% loading) for liquid phase Beckmann rearrangement of various ketoximes to the corresponding amides/lactams within 2 h in acetonitrile at reflux temperature. This is the first example of the application of the cyclopropenium ion as a catalyst, which opens up a new aspect of the synthetic utility of aromatic cation based catalysis.

Efficient one-pot synthetic protocols for iminosugar-bearing imidazo[1,2-a]pyridines from carbohydrates.

This letter describes two unprecedented one-pot high yielding synthetic approaches to imidazo[1,2-a]pyridine scaffolds from carbohydrates. The first approach involves microwave-assisted acid-catalyzed domino reactions of unprotected D-glucose/D-xylose with ammonium acetate and benzoin to afford polyhydroxy iminosugar-bearing tetrahydroimidazo[1,2-a]pyridines. In the second approach, polyhydroxy iminosugar-bearing tetrahydrobenzimidazo[1,2-a]pyridines were synthesized by using unprotected D-glucose/D-xylose and 1,2-diamines in the presence of 10 mol% of oxalic acid under solvent-free microwave irradiation conditions.

A novel multicomponent synthesis of polyfunctionalized bicyclic tetrahydropyrimidinone derivatives via mercaptoacetylative ring transformations.

A novel K-10 clay (nanoclay)-catalyzed expeditious synthesis of polyfunctionalized bicyclic pyrimidines using unprotected aldoses, 2-methyl-2-phenyl-1,3-oxathiolan-5-one and amidines/guanidine is reported. These polyfunctionalized bicyclic pyrimidines were obtained in excellent yields (72-93%) with high cis diastereoselectivity (>94%) at the ring junction via tandem condensation, mercaptoacetylative ring transformation and cyclization reactions. The process presents an excellent illustration of use of carbohydrates as renewable resources for the formation of pharmaceutically relevant fine chemicals employing solvent-free microwave irradiation conditions in a one-pot procedure.

An expeditious synthesis of benzoxazine-2-thione c-nucleosides Via Cu(OTf)2-mediated dehydrazinative beta-glycosylation.

A novel expeditious synthetic protocol for 1,3-benzoxazine-2-thione C-nucleosides via Cu(OTf)2-mediated dehydrazinative beta-glycosylation of 4-hydrazino-2H-benz[e]-1,3-oxazine-2-thiones with unprotected D-ribose is reported.

Novel salicylaldehyde-based mineral-supported expeditious synthesis of benzoxazin-2-ones.

One-pot montmorillonite K-10 clay supported reactions of either salicylaldehyde/2-hydroxyacetophenone hydrazones and aryl-/alkylureas or salicylaldehydes/2-hydroxyacetophenone and 4-aryl-/alkylsemicarbazides expeditiously yield 3,4-dihydro-4-hydrazino-2H-benz[e]-1,3-oxazin-2-ones (9) via cycloisomerization of the intermediate salicylaldehyde/2-hydroxyacetophenone 4-aryl-/alkylsemicarbazones (5) under solvent-free microwave irradiation. Under the same conditions, hydrazines (9) readily underwent reductive dehydrazination on alumina-supported copper(II) sulfate to furnish 2H-benz[e]-1,3-oxazin-2-ones (10).