Hydrophosphination of CO2 and Subsequent Formate Transfer in the 1,3,2‐Diazaphospholene‐Catalyzed N‐Formylation of Amines

Hydrophosphination of CO₂ with 1,3,2‐Diazaphospholene (NHP‐H; 1 ) afforded phosphorus formate (NHP‐OCOH; 2 ) through the formation of a bond between the electrophilic phosphorus atom in 1 and the oxygen atom from CO₂, along with hydride transfer to the carbon atom of CO₂. Transfer of the formate from 2 to Ph₂SiH₂ produced Ph₂Si(OCHO)₂ ( 3 ) in a reaction that could be carried out in a catalytic manner by using 5 mol % of 1 . These elementary reactions were applied to the metal‐free catalytic N‐formylation of amine derivatives with CO₂ in one pot under ambient conditions.     

K2CO3/H2O in [omim][BF4] Ionic Liquid: A Green Medium for Efficient Room‐Temperature Synthesis of N‐Substituted 1,4‐Benzoxazin‐3‐ones

A medium consisting of K₂CO₃ and H₂O in [omim][BF₄] ionic liquid (IL) was used to synthesize N‐substituted 2H‐benzo[b][1,4]oxazin‐3(4H)‐one derivatives from their corresponding o‐aminophenols and 2‐bromoalkanoates. As a result, chemoselective formation of benzoxazinones in high yields has been observed at room temperature. After the reactions and separation of the products, the IL was recovered and successfully reused in subsequent reactions without significant loss of activity.     

Ultrasound‐Promoted Catalyst‐Free Synthesis of 2,2′‐(1,4‐Phenylene)bis[1‐acetyl‐1,2‐dihydro‐4H‐3,1‐benzoxazin‐4‐one] Derivatives

A convenient approach to 2,2′‐(1,4‐phenylene)bis[1‐acetyl‐1,2‐dihydro‐4H‐3,1‐benzoxazin‐4‐one] derivatives 4 was explored employing the one‐pot condensation of anthranilic acids (=2‐aminobenzoic acids) 1 with terephthalaldehyde (=benzene‐1,4‐dicarboxaldehyde; 2 ) under ultrasound‐irradiation conditions (Scheme 1). The reactions proceeded smoothly in the presence of excess Ac₂O in the absence of any other catalyst and solvent to afford the respective products in high yields.     

Synthesis of Some Heterocyclic Compounds from 1H‐Indole‐2,3‐Dione: A Direct One‐Pot Synthesis of Spiro Indolone Derivatives

Some spiro indolone derivatives 5_a,b and 6 were synthesized through one‐pot synthesis via the ternary condensation of 1H‐indole‐2,3‐dione 1 , 3‐methyl‐1‐phenyl‐2‐pyrazolin‐5‐one 2 and active methylenes, namely malononitrile, ethyl cyanoacetate 4_a,b and pyrazolone 2 , respectively. The same derivatives can be obtained via other methods, through reactions of 3‐[3‐methyl‐5‐oxo‐1‐phenyl‐1,5‐dihydro‐pyrazol‐(4Z)‐ylidene]‐1,3‐dihydro‐indol‐2‐one 3 with the corresponding active methylenes. Reaction of 3 with amines and with ethyl vinyl ether was studied.     

Facile Chemoselective synthesis of 2‐(2‐(Methoxycarbonyl)‐3‐oxo‐2,3‐dihydrobenzofuran‐2‐yl)benzoic acids and 3H,3’H‐Spiro[benzofuran‐2,1′‐isobenzofuran]‐3,3′‐dione derivatives

Oxidation of some derivatives of 4b,9b–dihydroxyindeno[1,2‐b]benzofuran‐10‐one have been investigated in detail using lead(IV) acetate in acetic acid under reflux conditions and periodic acid in aqueous ethanol at room temperature. We realized that during the first 5–15 minutes of the oxidation reactions in lead(IV) acetate/acetic acid system, 3H,3’H‐spiro[benzofuran‐2,1′‐isobenzofuran]‐3,3′‐dione derivatives have been synthesized chemo selectively, while, if the reaction mixtures stirred for additional 3 hours, the main products would be 2‐(2‐(Methoxycarbonyl)‐3‐oxo‐2,3‐dihydrobenzofuran‐2‐yl)benzoic acids. Moreover, room temperature oxidation of 4b,9b–dihydroxyindeno[1,2‐b]benzofuran‐10‐ones by periodic acid (H₅IO₆), leads to the formation of 3H,3’H‐spiro[benzofuran‐2,1′‐isobenzofuran]‐3,3′‐dione derivatives in good to excellent yields.     

Novel and one‐pot Synthesis of Tetrahydropyrrolo[1,2‐a]‐2‐Methylbenzothiazole‐3‐Spiro‐1′‐Cyclohexa‐2′,5′‐Dien‐4′‐one‐4,5‐Dicarboxylate Derivatives via a Three Component Reaction

The three component condensation reactions involving 2‐methylbenzothiazole or 2,5‐dimethylbenzothiazole, dialkyl acetylenedicarboxylate, and 2,6‐dimethyl phenol or 2,6‐di‐tert‐butylphenol constitute a novel and one‐pot synthesis of tetrahydropyrrolo[1,2‐a ]‐2‐methylbenzothiazoles‐3‐spiro‐1^′‐cyclohexa‐2^′,5^′‐dien‐4^′‐one‐4,5‐dicarboxylate derivatives in good yields. The reactions proceeded at room temperature without using any catalyst. This method is very useful to functionalize benzothiazole derivatives in a one‐pot operation.     

Chemie freier,cyclischer vicinaler Tricarbonyl‐Verbindungen (`1,2,3‐Trione'), Teil 1, Reaktionsweise von Diazomethan und seinen Derivaten mit 5,5‐Dimethylcyclohexan‐1,2,3‐trion (=`Oxo‐dimedon') und verwandten Cyclohexan‐1,2,3‐trionen

Chemistry of Free Cyclic Vicinal Tricarbonyl Compounds (`1,2,3‐Triones'). Part 1. Reaction of Diazomethane and Its Derivatives with 5,5‐Dimethylcyclohexane‐1,2,3‐trione (=`Oxo‐dimedone') and Related Cyclohexane‐1,2,3‐triones Interactions of diazomethane and of its derivatives as typical nucleophiles with cyclic 1,2,3‐triones as efficient electrophiles lead to different results: a) formation of oxiranes (C,O insertion under loss of N₂), b) nucleophilic addition yielding diazoaldols, c) formation of ring‐enlargement products (C,C insertion under loss of N₂), and d) formation of dioxoles via redox reactions (under loss of N₂). Our results and those of other groups allow us to recognize that the unexpected outcome of the reaction of oxodimedone and several related species is due to a closed‐shell diazoaldol formation followed by an open‐shell redox reaction leading to dioxoles.     

Studies on the reactions of cyclic oxalyl compounds with hydrazines or hydrazones : Synthesis and reactions of 4‐benzoyl‐1‐(3‐nitrophenyl)‐5‐phenyl‐1H‐pyrazole‐3‐carboxylic acid

The 1H‐pyrazole‐3‐carboxylic acid 2 , obtained from the furan‐2,3‐dione 1 and N‐Benzylidene‐N'‐(3‐nitrophenyl) hydrazine, was converted via reactions of its acid chloride 3 with various alcohols or N‐nucleo‐philes into the corresponding ester or amide derivatives 4 or 5 , respectively. Nitrile 6 and anilino‐pyrazole acid 7 derivatives of 2 were also obtained by dehydration of 5a in a mixture of SOCl₂ with DMF and reduction of 2 with sodium polysulphide, respectively. While cyclocondensation reactions of 2 or 7 with phenyl hydrazine or hydrazine hydrate and 6 with only anhydrous hydrazine lead to derivatives of pyrazolo[3,4‐d]‐pyridazinone 8 and pyrazolo[3,4‐d]pyridazine amine 9 , respectivel. The reaction of 2 with 2‐hydrazinopyri‐dine provided hydrazono‐pyrazole acid derivative 10 , which was decarboxylated to give hydrazono‐pyra‐zole derivative 11 . Pyrazolo[4,3‐d]oxazinone 12 and 2‐quinolyl pyrazolo[3,4‐d]pyridazine 13 derivatives were also prepared by cyclocondensation reactions of 2 with hydroxylamine hydrochloride and 7 with acetaldehyde, respectively.     

Boron‐Based Catalysts for C−C Bond‐Formation Reactions

Because the construction of the C?C bond is one of the most significant reactions in organic chemistry, the development of an efficient strategy has attracted much attention throughout the synthetic community. Among various protocols to form C?C bonds, organoboron compounds are not just limited to stoichiometric reagents, but have also made great achievements as catalysts because of the easy modification of the electronic and steric impacts on the boron center. This review presents recent developments of boron‐based catalysts applied in the field of C?C bond‐formation reactions, which are classified into four kinds on the basis of the type of boron catalyst: 1) highly Lewis acidic borane, B(C₆F₅)₃; 2) organoboron acids, RB(OH)₂, and their ester derivatives; 3) borenium ions, (R₂BL)X; and 4) other miscellaneous kinds.     

Chemoselectivity in the Reaction of 2‐Diazo‐3‐oxo‐3‐phenylpropanal with Aldehydes and Ketones

The chemoselectivity in the reaction of 2‐diazo‐3‐oxo‐3‐phenylpropanal ( 1 ) with aldehydes and ketones in the presence of Et₃N was investigated. The results indicate that 1 reacts with aromatic aldehydes with weak electron‐donating substituents and cyclic ketones under formation of 6‐phenyl‐4H‐1,3‐dioxin‐4‐one derivatives. However, it reacts with aromatic aldehydes with electron‐withdrawing substituents to yield 1,3‐diaryl‐3‐hydroxypropan‐1‐ones, accompanied by chalcone derivatives in some cases. It did not react with linear ketones, aliphatic aldehydes, and aromatic aldehydes with strong electron‐donating substituents. A mechanism for the formation of 1,3‐diaryl‐3‐hydroxypropan‐1‐ones and chalcone derivatives is proposed. We also tried to react 1 with other unsaturated compounds, including various olefins and nitriles, and cumulated unsaturated compounds, such as N,N′‐dialkylcarbodiimines, phenyl isocyanate, isothiocyanate, and CS₂. Only with N,N′‐dialkylcarbodiimines, the expected cycloaddition took place.     

One‐Pot Syntheses of 2‐(2‐Sulfanyl‐4H‐3,1‐benzothiazin‐4‐yl)acetic Acid Derivatives via Reactions of 3‐(2‐Isothiocyanatophenyl)prop‐2‐enoic Acid Derivatives with Thiols or Sodium Sulfide

Two efficient methods for the preparation of 2‐(2‐sulfanyl‐4H‐3,1‐benzothiazin‐4‐yl)acetic acid derivatives 3 under mild conditions have been developed. The first method is based on the reaction of 3‐(2‐isothiocyanatophenyl)prop‐2‐enoates 1a – 1c with thiols in the presence of Et₃N in THF at room temperature, leading to the corresponding dithiocarbamate intermediates 2 , which underwent spontaneous cyclization at the same temperature by an attack of the S‐atom at the prop‐2‐enoyl moiety in a 1,4‐addition manner (Michael addition) to give 2‐(2‐sulfanyl‐4H‐3,1‐benzothiazin‐4‐yl)acetates in one pot. The second method involves treatment of 3‐(2‐isothiocyanatophenyl)prop‐2‐enoic acid derivatives 1b – 1d with Na₂S leading to the formation of 2‐(2‐sodiosulfanyl‐4H‐3,1‐benzothiazin‐4‐yl)acetic acid intermediates 5 by a similar addition/cyclization sequence, which are then allowed to react with alkyl or aryl halides to afford derivatives 3 . 2‐(2‐Thioxo‐4H‐3,1‐benzothiazin‐4‐yl)acetic acid derivatives 6 can be obtained by omitting the addition of halides.     

Facile Synthesis of Novel 3‐(4‐phenylisothiazol‐5‐yl)‐2H‐chromen‐2‐one Derivatives as Potential Anticancer Agents

A series of 3‐(4‐phenylisothiazol‐5‐yl)‐2H‐chromen‐2‐one ( 6a – l ) derivatives has been efficiently synthesized by straightforward sequential reactions. Tandem Vilsmeier Hack reaction/cyclization/bromination/Suzuki cross‐coupling reactions were successfully applied to the preparation of title compounds in good‐to‐high yields. In the synthetic sequences, 3‐chloro‐3‐(2‐oxo‐2H‐chromen‐3‐yl)acrylaldehydes ( 2 ) were found to react with ammonium thiocyanate to yield the corresponding 3‐(isothiazol‐5‐yl)‐2H‐chromen‐2‐ones ( 3 ). These derivatives were brominated with N‐bromo succinamide to yield the corresponding regioselective 3‐(4‐bromoisothiazol‐5‐yl)‐2H‐chromen‐2‐one ( 4 ). Finally, compound 4 was treated with various phenyl/pyrazole/7H –pyrrolo[2,3‐d]pyrimidinyl boronic acids 5a – l in the presence of K₂CO₃ and Pd catalyst in dimethylformamide to yield the corresponding title derivatives 6a – l . All the synthesized compounds were characterized by analytical and spectral studies. All the final compounds were screened against different cancer cell lines (A549, PC3, SKOV3, and B16F10), and among these compounds, 6b , 6g , 6h , and 6l displayed moderate cytotoxic activity against the tested cell lines.     

An Efficient and Green One‐pot Synthesis of 12‐Aryl‐8,9,10,12‐tetrahydrobenzo[a]xanthen‐11‐one Derivatives Promoted by Sulfamic Acid in [BMIM]BF4 Ionic Liquid

An efficient and green procedure for the synthesis of novel 12‐aryl‐8,9,10,12‐tetrahydrobenzo[a]xanthen‐11‐one derivatives has been described through one‐pot condensation of 2‐naphthol, arylaldehyde and 5,5‐dimethyl‐cyclohexane‐1,3‐dione in the presence of sulfamic acid (NH₂SO₃H) in ionic liquid 1‐n‐butyl‐3‐methylimidazolium tetrafluoroborate ([BMIM]BF₄). These reactions proceed with good yields under short reaction time. Furthermore, the green catalytic system can be recycled specific times with no decreases in yields and reaction rates.     

One‐pot Method for Reduction of Pyrazolo[5,1‐c][1,2,4]Triazine‐7‐diazonium Tetrafluoroborate to 7‐Hydrazinyl Derivatives

New convenient one‐pot method for reduction of hetarenediazonim tetrafluoroborates to the hetarylhydrazine derivatives was developed. Interaction of 8‐carboxyethyl‐3‐(tert‐butyl)‐4‐oxo‐4,6‐dihydropyrazolo[5,1‐c ][1,2,4]triazine‐7‐diazonium tetrafluoroborate with anhydrous SnCl₂ in anhydrous CF₃CO₂H, and further sequence of one‐pot operations led to formation of various derivatives of the unstable ethyl 3‐(tert‐butyl)‐7‐hydrazinyl‐4‐oxo‐4,6‐dihydropyrazolo[5,1‐c ][1,2,4]triazine‐8‐carboxylate (hydrochloride, hydrazides, hydrazones, and pyrazoles), which were isolated in high yields. The anhydrous conditions were first used with SnCl₂ and allowed to exclude hydrolysis of the ester group and formation of the by‐products.     

Lewis Acid Catalyzed Synthesis of 1‐Aryl‐1,2‐dihydro‐naphtho[1,2‐e][1,3]oxazin‐3‐ones under Solvent Free Conditions: A Mechanistic Approach

Lewis acids catalyzed highly efficient one‐pot three component coupling of β‐naphthol, benzaldehydes and urea to produce 1‐aryl‐1,2‐dihydro‐naphtho[1,2‐e][1,3]oxazin‐3‐one derivatives under solvent free conditions is described. Mechanistic studies confirmed that product formation is possible only at very high temperature (140–150°C) and at lower temperature (90–100°C) formation of 14‐aryl‐14H‐dibenzo(a,j)xanthenes was observed. Among the nine Lewis acids screened, iodine, P₂O₅ and Yb(OTf)₃ are found to be most effective catalyst for this multicomponent reaction.     

Microwave‐Assisted,Rhodium(III)‐Catalyzed N‐Annulation Reactions of Aryl and α,β‐Unsaturated Ketones with Alkynes

New Rh^III‐catalyzed, one‐pot N‐annulation reactions of aryl and α,β‐unsaturated ketones with alkynes in the presence of ammonium acetate have been developed. Under microwave irradiation conditions, the processes lead to rapid formation of the respective isoquinoline and pyridine derivatives with efficiencies that are strongly dependent on the steric nature of the aryl ring and enone substituents. By employing this protocol, a variety of isoquinoline and pyridine derivatives were prepared in high yields. In addition, a new one‐pot approach to the synthesis of pyridines, involving four‐component reactions of ketones, formaldehyde, NH₄OAc, and alkynes, has been uncovered. This process takes place through a route involving initial aldol condensation of the ketone with formaldehyde to generate a branched α,β‐unsaturated ketone that then undergoes Rh^III‐catalyzed N‐annulation with NH₄OAc and the alkyne.     

Synthesis of 4‐silaspiro[3.4]octa‐1,5‐diene derivatives: hybrid spiro compounds

Trialkynyl(vinyl)silanes CH₂?CH? Si(C?C? R)₃ (R = Bu, Ph, p‐tolyl) were prepared and treated with 9‐borabicyclo[3.3.1]nonane (9‐BBN). Consecutive 1,2‐hydroboration and intramolecular 1,1‐carboboration reactions (each requires different reaction conditions) were studied. 1,2‐Hydroboration of the Si? vinyl group takes place at ambient temperature (23°C in tetrahydrofuran), followed by intramolecular 1,1‐vinylboration to give 1‐silacyclopent‐2‐ene derivatives, bearing still two alkynyl functions at the silicon atom. Further treatment with a second equivalent of 9‐BBN affords 1‐alkenyl‐1‐(alkynyl)‐1‐silacyclopent‐2‐ene derivatives. These undergo intramolecular 1,1‐vinylboration to give 4‐silaspiro[3.4]octa‐1,5‐dienes bearing the boryl groups at 2 and 6 positions. Protodeborylation of all new compounds (intermediates and final products) using acetic acid in slight excess afforded corresponding silanes including spirosilanes. All compounds were characterized using multinuclear NMR spectroscopy (¹H, ¹¹B, ¹³C, ²⁹Si) in solution state. Solid‐state structures for one of the trialkynyl(vinyl)silanes (R = p‐tolyl) and one of the 1‐silacyclopent‐2‐ene derivatives (R = Ph) were confirmed using X‐ray diffraction. Copyright © 2015 John Wiley & Sons, Ltd.     

Short Syntheses of some ‘Decalin‐1,8‐diones’ and their Derivatives: Breaking the Pretended Symmetry

A cheap synthesis of the so‐called ‘decalin‐1,8‐diones’ started with the conjugate (1,4‐) addition of cyclohex‐2‐en‐1‐one derivatives to the γ‐position of the dilithium derivative (buta‐1,3‐diene‐1,1‐bis(olate)) of crotonic acid. Hydrogenation of these ‘1,4‐γ’ adducts and final cyclization afforded the enol tautomers of decalin‐1,8‐diones. Nucleophilic substitutions at these 3‐oxoenols by NH₃ or primary amines created only monoamino products (namely, 3‐oxoenamines) whose reactions with OPCl₃ yielded dihydro(1,3,2)oxazaphosphinin‐2‐one derivatives. The two regioisomers of a trimethyl‐3‐oxoenamine served as models for the constitutional assignments of the two rapidly interconverting (hence, individually NMR‐invisible), tautomeric trimethyl‐3‐oxoenols. Such methyl substitutions served to break the ‘pretended’ symmetry of ‘decalin‐1,8‐dione’. Hydrazine and 3‐oxoenols furnished oxygen‐free indazole derivatives whose N?H bonds exchanged with t_1/2=ca. 0.00035 s at ca. ?58(9) °C.     

Michael-Addition Reaction of Malononitrile with α,β-Unsaturated Cycloketones Catalyzed by KF／Al2O3

A series of KF/Al2O3 catalyzed Michael-addition reactions between malononitrile and α,β-unsaturated cycloketones in DMF solution were studied. At room temperature, 2-cyano-3-aryl-3-(1,2,3,4-tetrahydronaphthalen-1-one-2-yl) propionitrile derivatives were synthesized by the reaction between 2-arylmethylidene-1,2,3,4-tetra-hydronaphthalen-1-one and malononitrile. However, if the temperature was increased to 80℃, 2-amino-3-cyano-4-aryl-4H-benzo[h]chromene derivatives were obtained in high yields. When the α,β-unsaturated ketones were replaced by 2,6-biarylmethylidenecyclohexanone or 2,5-biarylmethylidenecyclopentanone, another series of 2-amino-3-cyano-4H-pyran derivatives was isolated successfully. The structures of the products were confirmed by X-ray diffraction analysis.     

One‐Pot Synthesis of Pyrrolo[1,2‐a]quinolin‐1‐ones by the Cyclocondensation of 5‐Hydroxy‐1‐arylpyrrolidin‐2‐ones with Dicarbonyls

A one‐pot synthesis of pyrrolo[1,2‐a]quinolin‐1‐ones has been developed from the reactions of 5‐hydroxy‐1‐arylpyrrolidin‐2‐ones with 1,3‐dicarbonyl compounds under the promotion of H₃PO₄/P₂O₅ or HOAc/H₂SO₄. The pyrrolo[1,2‐a]quinolin‐1‐ones are formed by two‐step reactions, that is, the coupling of N‐acyliminium ion intermediates produced from 5‐hydroxy‐1‐arylpyrrolidin‐2‐ones with 1,3‐dicarbonyls and subsequent Friedel–Crafts reactions of the resulting ketone with the aryl ring.