ortho-Induced transition-metal-free C-arylation cyclization reaction for the synthesis of polysubstituted isocoumarins

A new protocol for the synthesis of polysubstituted isocoumarins from 2-iodobenzoic acid and β-diketone compounds has been developed. The occurrence of C-arylation cyclization reaction in transition-metal-free systems and ortho-induced substrates has been exploited. Reactions using these inexpensive conditions have displayed high functional group tolerance and excellent yields.     

Chlorosulfonic acid-mediated cyclization of 4-phenyl-3-isocoumarincarboxylic acids and 4-phenyl-3-isoquinolinonecarboxylic acids: an efficient synthesis of 3-oxoindeno[2,1-c]isocoumarins and 3-oxoindeno[2,1-c]isoquinolinones

A highly efficient and clean method has been developed for the synthesis of 3-oxoindeno[2,1-c]isocoumarins and 3-oxoindeno[2,1-c]isoquinolinones from 4-phenyl-3-isocoumarincarboxylic acids and 4-phenyl-3-isoquinolinonecarboxylic acids, respectively.     

Palladium(II)-catalyzed tandem annulation reaction of o-alkynylbenzoates with methyl vinyl ketone for the synthesis of isocoumarins

A palladium(II)-catalyzed highly regioselective tandem reactions of o-alkynylbenzoates with methyl vinyl ketone for the synthesis of isocoumarins was developed. It is a convenient, mild and environmentally benign reaction with moderate to high yield. The reaction is initiated by the Pd(II) species and regenerate the Pd(II) species to complete the catalytic cycle without the necessity of a redox system.     

An atom-economic and odorless thia-Michael addition in a deep eutectic solvent

The first 100% atom-efficient and odorless protocol for carbon–sulfur bond formation in a deep eutectic solvent (DES) as both the reaction medium and catalyst is reported. The biodegradable and inexpensive DES provides an efficient and convenient ionic reaction medium for the thia-Michael addition with in situ generation of S-alkylisothiouronium salts in place of thiols without the urea by-product segment. This protocol offers several advantages including short reaction times, high yields, clean reactions, and inexpensive and commercially available starting materials.     

Palladium/copper-catalyzed tandem Sonogashira coupling/lactonization of methyl 2-(2′,2′-dibromovinyl)benzoate with terminal alkynes: Facile access to 3-alkynyl isocoumarins

An efficient palladium/copper-catalyzed tandem Sonogashira reaction/lactonization of methyl 2-(2′,2′-dibromovinyl)benzoate with terminal alkynes has been developed. This facile and direct approach furnishes a variety of 3-alkynyl isocoumarins in moderate to good yields under mild reaction conditions. Furthermore, this method enables concise total synthesis of natural products 3′-hydroxycorfin and gymnopalynes A.     

Boric acid in aqueous micellar medium: an effective and recyclable catalytic system for the synthesis of aryl-7,8-dihydro[1,2,4]triazolo[4,3-a]pyrimidine-6-carbonitriles

A simple, green, and efficient protocol is reported for the preparation of aryl-7,8-dihydro[1,2,4]triazolo[4,3-a]-pyrimidine-6-carbonitriles through one-pot multi component reaction using substituted aromatic aldehydes, malononitrile, and 3-amino[1,2,4]triazole. The reaction is catalyzed by boric acid in aqueous micellar condition. Present protocol incorporates environmentally non-hazardous reaction condition, easy work-up, and use of recyclable catalytic system with associated benefits like excellent yield (84–96%) and shorter reaction time (20 min). Proposed methodology offers rapid access to substituted aryl-7,8-dihydro[1,2,4]triazolo[4,3-a]pyrimidine-6-carbonitriles with high atom-economy and catalytic efficiency.     

Copper-catalyzed annulation of 2-bromobenzoic esters with terminal alkynes towards 3-substituted isocoumarins

An efficient method for the synthesis of 3-substituted isocoumarins that are an important class of biologically active scaffolds via annulation of 2-bromobenzoic esters with terminal alkynes by copper catalyzed is described. The advantages of this method include mild reaction conditions, high yield and regioselectivity, and wide tolerance toward functional groups.     

Enantioselective organocatalytic synthesis of the chiral chromenes by domino oxa-Michael-aldol reaction

The proline based chiral organocatalyst has been found to be an efficient catalyst for enantioselective domino oxa-Michael-aldol reaction. This catalytic system provided the synthesis of substituted 2-aryl-2H-chromenes-3-carbaldehyde in good to high yields (73%–97%) with excellent enantioselectivity (up to 97%) and reasonable reaction times. The atom economy, high yield and mild reaction conditions are some of the important features of this protocol.     

Synthesis of 3-substituted isocoumarins via a cascade intramolecular Ullmann-type coupling-rearrangement process

A simple and highly efficient strategy for the synthesis of 3-substituted isocoumarins through a copper(I)-catalyzed reaction of 1-(2-halophenyl)-1,3-diones has been developed. The procedure is based on a cascade copper-catalyzed intramolecular Ullmann-type C-arylation and rearrangement process. This methodology is tolerant of a wide range of substrates and applicable to library synthesis.     

Assembly of 3-substituted isocoumarins via a CuI-catalyzed domino coupling/addition/deacylation process

An efficient strategy for the synthesis of a variety of 3-substituted isocoumarins has been developed. The reaction proceeded from o-halobenzoic acids and 1,3-diketones via a copper(I)-catalyzed domino reaction in DMF under the action of K(3)PO(4) at 90-120 °C without a ligand to afford the corresponding 3-substituted isocoumarin derivatives in good to excellent yields. o-Halobenzoic acids could be o-iodobenzoic acid, o-bromobenzoic acid, and o-chlorobenzoic acid derivatives. 1,3-Diketones could be alkyl- and aryl-substituted 1,3-diketones.     

Organocatalytic formal [5+1] annulation: diastereoselective cascade synthesis of functionalized six-membered spirocyclic indane-1,3-diones/oxindoles via Michael–aldol reaction

An efficient cascade protocol has been developed for the diastereoselective synthesis of functionalized six-membered spirocyclic compounds. The reaction proceeded smoothly between indane 1,3-diones/oxindoles/coumaranone as the dinucleophilic components and (E)-5-nitro-6-aryl-hex-5-en-2-one as the dielectrophile to give the desired products with reasonable to high chemical yields (30–84%) and high levels of diastereoselectivities (upto >95:5 dr). The reaction proceeded smoothly via cascade Michael–aldol reaction.     

Efficient method for the oxidation of aldehydes and diols with tert-butylhydroperoxide under transition metal-free conditions

An efficient, mild, and simple protocol is presented for the oxidation of aldehydes and diols to carboxylic acids utilizing 70% aq TBHP as oxidant and t-BuOK as additive. The oxidation of aldehydes could be achieved by two methods under aqueous medium. Excellent yields of products were obtained in short reaction times. Notably, the products were isolated by simple filtration technique and do not involve chromatographic separation. These reactions may prove to be valuable alternatives to traditional metal-mediated oxidations. Oxidation does not require any transition metals or organic solvents in reaction, making this protocol green.     

Synthesis of 3-arylisocoumarins, including thunberginols A and B, unsymmetrical 3,4-disubstituted isocoumarins, and 3-ylidenephthalides via iodolactonization of methyl 2-ynylbenzoates or the corresponding carboxylic acids

3-Aryl-4-iodoisocoumarins, which were readily and efficiently prepared by regioselective iodolactonization of methyl 2-ynylbenzoates or the corresponding carboxylic acids, were used as precursors either to 3-arylisocoumarins, including naturally-occurring thunberginols A and B, or to unsymmetrical 3,4-disubstituted isocoumarins. On the other hand, (Z)- and (E)-3-iodomethylidenephthalides, which were regioselectively prepared by iodolactonization of methyl 2-ethynylbenzoate, were employed as starting materials for the stereospecific synthesis of (Z)- and (E)-3-ylidenephthalides, respectively. Some 3-arylisocoumarins and unsymmetrical 3,4-disubstituted isocoumarins showed certain cytotoxic activity against human cancer cell lines in vitro.     

Polyethylene glycol (PEG-400): an efficient and recyclable reaction medium for the synthesis of pyrazolo[3,4-b]quinoline derivatives

A simple, efficient, and eco-friendly synthetic protocol has been developed via one pot three-component reaction between aldehyde, amino pyrazole, and 1,3-cyclohexanedione by using recyclable polyethylene glycol (PEG)-400 as a reaction medium. Utilizing this protocol a variety of pyrazolo[3,4-b]quinoline derivatives were synthesized in excellent yields.     

Facile synthesis of substituted pyrrole-fused isocoumarins from ninhydrin

A simple and efficient procedure has been developed for the synthesis of substituted pyrrole-fused isocoumarins from easily available ninhydrin. The cyclic hemiaminal dihydroxy-indenopyrroles, the adducts of ninhydrin with enamines of acetylacetone, give pyrrole-fused isocoumarins upon heating in acidic medium. The process constitutes an interesting acid-catalyzed rearrangement to eight-membered lactams followed by intramolecular cyclization involving the amino and keto groups.     

CeCl3·7H2O: a highly efficient catalyst for the synthesis of 1-substituted-octahydro-[1,3,2]diazaphospholo[1,5-a]pyridine-1-oxide

An efficient and simple protocol is reported for the synthesis of a new class of 1-substituted-octahydro-[1,3,2]diazaphospholo[1,5-a]pyridine-1-oxides in good to excellent yield (88–95%) via Michaelis–Arbuzov rearrangement. Condensation of diamido phosphite with various halides at 60 °C using CeCl₃·7H₂O as a highly efficient catalyst afforded the products within a short period of reaction time. This procedure is mild, efficient, and non-toxic and stability of the catalyst is the merit of this process. Therefore, this protocol being environmentally benign and efficient, serves as an alternative procedure for the preparation of the title compounds.     

An efficient synthesis of isocoumarins via a CuI catalyzed cascade reaction process

3-Alkyl isocoumarins are provided by CuI/amino acid-catalyzed Sonogashira coupling reaction of o-bromo benzoic acids and terminal alkynes and the subsequent additive cyclization. This cascade process allows synthesis of diverse isocoumarins by varying both coupling partners bearing a wide range of functional groups.     

L-tert-Leucine derived urea-ammonium salts: Efficient bifunctional phase transfer catalysts for highly diastereo- and enantioselective aza-Henry reaction of isatin-derived N-Boc ketimines with α-aryl nitromethanes

An efficient way of aza-Henry reaction between isatin-derived N-Boc ketimines and α-aryl nitromethanes catalyzed by bifunctional phase transfer catalysts with a quaternary ammonium center derived from L-tert-Leucine has been developed. A series of 3-substituted 3-amino-oxindoles were constructed by this catalytic protocol in excellent yields (90–99%), with high enantioselectivities (83–95%) and diastereoselectivities (79:21–97:3). The asymmetric aza-Henry reaction of N-Boc amidosulfones and α-aryl nitromethanes were also investigated and gave the corresponding products in high to excellent yields (72–97%) with high enantioselectivities (up to 99%) and diastereoselectivities (up to >99:1).     

Ultrasound assisted green synthesis of bound type bis-heterocyclic carbazolyl imidazo[1,2-a]pyridines via Groebke-Blackburn-Bienayme reaction

A series of seventeen novel 3-imidazo[1,2-a]pyridine carbazoles bound type bis-heterocycles were synthesized by Ultrasound irradiation (USI) assisted Groebke-Blackburn-Bienaymé reaction (GBBR), by employing ammonium chloride (10?mol%) as a catalyst in excellent yields (90–96%). This new, efficient and mild protocol has silent features such as green inexpensive and easily available catalyst and solvent at room temperature.     

Singlet oxygen mediated one pot synthesis of N-pyridinylamides via oxidative amidation of aryl alkyl ketones

An environmental friendly, efficient protocol has been realized for the synthesis of N-pyridinylamides via copper catalyzed oxidative amidation of aryl alkyl ketones with 2-aminopyridines. This one pot protocol involves chemo selective cleavage of C (O)–C bond in the presence of singlet oxygen. The reaction conditions are simple, tolerates wide range of substrates and the products were formed in good to excellent yields. This method offers a moderate improvement over the earlier successful attempts in generating N-pyridinylamides.