Anaerobic environment as an efficient approach to improve the photostability of fatty acid photodecarboxylase

Fatty acid photodecarboxylase of Chlorella variabilis NC64A (CvFAP) is a novel photoenzyme with great potential in the treatment of waste lipids and production of sustainable aviation fuel. However, the fragile nature of CvFAP to blue light is an urgent challenge. Herein, we demonstrated anaerobic environment could significantly improve the photostability of CvFAP for the first time. The decarboxylation of palmitic acid by CvFAP for 3 h under anaerobic environment increased pentadecane yield by 44.7% as compared to that under aerobic environment. The residual activity of CvFAP after blue-light preillumination in the absence of palmitic acid for 0.5 h under anaerobic environment was 80.4%, which was 258.7 times higher than that under aerobic environment. Remarkable accumulation of superoxide radical and singlet oxygen in CvFAP under aerobic environment led to the poor photostability of CvFAP. Anaerobic environment helped to mitigate the production of superoxide radical and singlet oxygen in CvFAP, improving the photostability of CvFAP.     

High pressure and thermal Diels-Alder reactions of 5-nitro[2.2]paracyclophanepyran-6-one

The Diels-Alder reactions of 5-nitro[2.2]paracyclophanepyran-6-one with 1,3-butadienes and 1,2-dihydro-3-vinyl-naphthalene were examined under thermal and high-pressure conditions. The cycloadditions with 1,3-butadienes occurred in good yield and anti-exo diastereoselectively only under high-pressure conditions; the one with 1,2-dihydro-3-vinyl-naphthalene afforded comparable yields of mixtures of anti/syn adducts under normal and high-pressure conditions. A structural analysis of the reaction products by ¹H and ¹³C NMR spectroscopy is presented.     

Radical cyclizations to quinolone and isoquinolone systems under oxidative and reductive conditions

Radical cyclizations to quinolone and isoquinolone systems under Fenton-type and n-Bu₃SnH-mediated conditions are described. For N-iodoalkylquinolones, ca. 3:1 mixtures of oxidative cyclization products at C-2, and unexpectedly at C-8, were obtained under both conditions. Five- or six-membered oxidative cyclization products were obtained from N-iodoalkylisoquinolones under Fenton-type conditions, whereas n-Bu₃SnH-mediated reactions gave products of reductive cyclization in the five, six, and seven-membered series.     

The stereodivergent aziridination of allylic carbamates, amides and sulfonamides

A stereodivergent protocol for the aziridination of a range of cyclic allylic amine derivatives has been developed. syn-Products can be obtained in >99:1 dr under H-bonded control and anti-products are obtained in >99:1 dr under steric control by judicious choice of the N-protecting groups.     

One-pot synthesis of novel spiro 2,3,7,8-tetrahydro-benzo[1,2-b:5,4-b′]dipyran-4,6-dione and 2,3,8,9-tetrahydro-benzo[1,2-b:4,3-b′]dipyran-4,10-dione derivatives

An efficient synthesis of novel spiro 2,3,7,8-tetrahydro-benzo[1,2-b:5,4-b′]dipyran-4,6-dione and 2,3,8,9-tetrahydro-benzo[1,2-b:4,3-b′]dipyran-4,10-dione derivatives in high yields under microwave irradiation is described. The reaction was also studied under conventional heating conditions.     

Convergence of products from Povarov and von Miller reactions: approaches to helquinoline

Yttrium triflate or triflic acid catalysed Povarov reaction of methyl anthranilate with ethyl vinyl ether, both as aldehyde surrogate and as alkene, gave the desired 2-methyl-4-ethoxytetrahydroquinoline diastereoisomers as the major products along with four component coupling von Miller adducts. A proton NMR-study, using yttrium triflate as catalyst, revealed that the cis-diastereoisomers were the initial major products in both the Povarov and von Miller reactions but that these isomerised to the trans-diastereoisomers under the reaction conditions. Two distinct pathways for forming von Miller adducts were uncovered with the initial Povarov products being converted to von Miller adducts under the reaction conditions. Replacement of the 4-ethoxy with a 4-methoxy group under acidic conditions gave predominantly the trans-diastereoisomer, which was subsequently converted to a cis/trans mixture of the tetrahydroquinoline antibiotic helquinoline. It was also possible to convert the von Miller products to Povarov products under acidic conditions.     

Highly regioselective Wittig reactions of cyclic ketones with a stabilized phosphorus ylide under controlled microwave heating

Significant base and temperature effects on the Wittig reactions of cyclohexanones with (carbethoxymethylene)triphenylphosphorane under microwave irradiation were observed. For the Wittig reactions carried out in a domestic microwave oven under solvent-free conditions, the initially formed exo-olefin products isomerized into the thermodynamically more stable endo-olefins due to uncontrolled high reaction temperature. In sharp contrast, under controlled microwave heating, both exo- and endo-olefins have been selectively synthesized by accurately regulating the reaction temperature with or without a base.     

Convenient synthesis of fused pyrano[3,2-h]- and furo[3,2-h]benzo[f]coumarins from naphthalene-2,3-diol

The treatment of 8-propargyloxy-benzo[f]coumarin with boron trifluoride diethyl etherate in N,N-dimethylformamide under reflux or MW irradiation resulted in pyrano[3,2-h]benzo[f]coumarin, while the furo[3,2-h]benzo[f]coumarin is received from the treatment with N-methylformamide under MW irradiation.     

Investigation of m-nitroaniline formation during the Zimmermann reaction

The Zimmermann reaction for the determination of 17-ketosteroids was tested under both room-temperature and steam-distillation reaction conditions. meta-Nitroaniline was isolated from the residue of the steam distillation by ether extraction and thin-layer chromatography. Conclusive identification was by infrared spectroscopy. In contrast, m-nitroaniline was not formed under room-temperature reaction conditions, even when allowed to react for 24 hr. Similar results were also obtained for the reaction between acetone and m-dinitrobenzene under alkaline conditions. In conclusion, the results indicate that m-nitroaniline formation cannot account for the conversion of structure I to structure II under room-temperature reaction conditions as investigated herein.     

Co- and homocyclotrimerization reactions of protected 1-alkynyl-2-deoxyribofuranose. Synthesis of C-nucleosides, C-di- and C-trisaccharide analogues

Cyclotrimerization of β- or α-ethynyl-3,5-di-O-toluoyl-2-deoxy-d-ribofuranose with α,ω-diynes proceeded smoothly under Rh-catalysis to afford the corresponding β- or α-benzene C-nucleoside derivatives. Analogous co-cyclotrimerization of α- or β-propynyl- and -phenylethynyl-3,5-di-O-toluoyl-2-deoxy-d-ribofuranose with α,ω-diynes gave the corresponding arene derivatives only under microwave irradiation in the presence of a Rh-catalyst in moderate yields. Attempted homocyclotrimerization of β- or α-ethynyl-3,5-di-O-toluoyl-2-deoxy-d-ribofuranose under Rh-catalysis led only to enynes while the use of Ru-catalyst gave the desired 1,2,4- and 1,3,5-tri-(2-deoxyribofuranose-1-yl)benzene.     

One-pot facile synthesis of acridine derivatives under solvent-free condition

N,N’-Dibromo-N,N’-1,2-ethanediylbis(p-toluenesulfonamide) [BNBTS] as a reusable catalyst promoted one-pot synthesis of benzo[c]acridines in good to high yields under three-component reaction from anilines, aldehydes and cyclic 1,3-dicarbonyl compounds under solvent-free conditions.     

Efficient and scalable arylation of bicyclic lactones to form quaternary centers using conventional and microwave radiation

Easily accessible bicyclic lactones were efficiently arylated under modified Hartwig and Buchwald conditions to form quaternary aryl centers with complete cis selectivity. This series is notable in that unreactive substrates, including sterically-demanding ortho-substituted aromatic compounds, enjoyed significant rate acceleration under microwave radiation. Additionally, it was noted that the reactions could be accomplished under standard anaerobic conditions and on multi-gram scale.     

Transition metal and base free coupling of N-tosylhydrazones with 1,3-dicarbonyl compound

N-tosylhydrazones derived from a wide variety of aryl, alkyl and heteroaryl aldehydes undergo smooth coupling with 5,5-dimethylcyclohexane-1,3-dione under transition metal and base free conditions to generate tetraketo compounds in high yields. In presence of a base, the coupling reaction generates β-keto enol ether as the major product in a polar aprotic solvent. N-Tosylhydrazone can also be converted to xanthenedione in high yields in one-pot operation under mild acidic conditions.     

Aza-Diels-Alder reactions in ionic liquids: a facile synthesis of pyrano- and furanoquinolines

Room temperature ionic liquids are found to catalyze efficiently the three component-coupling reactions of aldehydes, amines and cyclic enol ethers such as 3,4-dihydro-2H-pyran and 2,3-dihydrofuran under mild and convenient conditions to afford the corresponding pyrano- and furanoquinolines in excellent yields with high endo-selectivity. Interestingly, 2,3-dihydrofuran afforded selectively endo-products under the similar reaction conditions.     

A new practical synthesis of 3-amino-substituted 5-aminopyrazoles and their tautomerism

It was found that 3-amino-substituted 5-aminopyrazoles could be effectively prepared via hydrolytic decarboxylation of the corresponding 3,5-diaminopyrazole-4-carboxylates under microwave irradiation. The reactions required short time (4?min) and were successfully reproduced in a larger scale and under conventional heating mimicking the microwave heating pattern. X-ray crystallography identified two different types of tautomers in crystals of related 5-aminopyrazoles with p-toluidyl and p-anisidyl moieties at the position 3, respectively.     

Photochemical synthesis of benzoxazolo[3,2-b]isoquinolin-11-one and isoquinolino[3,2-b][1,3]benzoxazin-11-one under basic conditions

Irradiation of N-phenyl substituted isoquinolines in acetonitrile containing 1 M NaOH in a multilamp reactor (MLR) furnished benzoxazolo[3,2-b]isoquinolin-11-ones. In contrast, irradiation of the N-benzyl substituted isoquinoline derivative under the same conditions afforded the hydrolysed N-benzylbenzamide derivative. The isoquinolinobenzoxazine was obtained by irradiating the N-benzyl substituted isoquinoline derivative at higher basic conditions. The required isoquinolines were synthesized under solvent-free, solid supported microwave conditions.     

Unprecedented InCl3-catalyzed formation of cis-fused perhydrofuro[2,3-b]oxepines

2-Methylindole and its N-substituted derivatives react smoothly with 2,3-dihydrofuran (DHF) in the presence of a catalytic amount of InCl₃ under mild conditions to afford the corresponding 2-methyl-3-perhydrofuro[2,3-b]oxepin-4-yl-1H-indole derivatives in fairly good yields with high diastereoselectivity, while 3,4-dihydro-2H-pyran (DHP) affords exclusively 5,5-di(1H-3-indolyl)-1-pentanol derivatives in high yields under similar reaction conditions.     

Synthesis of N-aryl-3-(arylimino)-3H-indol-2-amines via hypervalent iodine promoted oxidative diamination of indoles

A direct and fast oxidative diamination of substituted indoles with anilines was realized by using 1-fluoro-1,2-benziodoxol-3(1H)-one under mild conditions. This protocol could provide a wide range of synthetically valuable N-aryl-3-(arylimino)-3H-indol-2-amine derivatives under peroxide-free conditions within 30?min in up to 91% yields.     

Benign synthesis of thiophosphates,thiophosphinates and selenophosphates in neat condition using N-chalcogenoimides as the source of electrophilic sulfur/selenium

A neat reaction protocol has been developed for synthesis of thiophosphate, thiophosphinate and selenophosphate compounds. N-chalcogenoimides have been used for chalcogenylation of P(O)H moieties of various H-phosphonates under solvent, catalyst and base free condition at room temperature in aerial atmosphere. Both S-aryl and S-alkyl phosphorothioate compounds were prepared by this method in good yields. Selenophosphates were also synthesized using N-(phenylseleno)phthalimide under solvent free condition.     

Reactions of chloroalkyl-gem-dichlorocyclopropanes with amines

N-Alkylation of primary and secondary amines with monochloroalkyl-gem-dichlorocyclopropanes under conditions of thermal and microwave heating results in the corresponding amino-gem-dichlorocyclopropanes. With microwave irradiation heating, the reaction time has been decreased to 1 h, the yields of the amines containing gem-dichlorocyclopropane moiety being the same. Formation of the bicyclic amine in reaction of cis-2,3-dichloromethyl-gem-dichlorocyclopropane with primary amines under conditions of phasetransfer catalysis has been studied.