Search

A visible-light-promoted transfer hydrogenation of azobenzenes has been developed. In the presence of B2pin2 and upon visible-light irradiation, the reactions proceeded smoothly in methanol at ambi...

Methods for the synthesis of 1,2,4-triazolidines are scarce. Herein, we report a visible-light-promoted decarboxylative addition cyclization of N-aryl glycines and azobenzenes to access such important compounds. Using commercially available methylene blue (MB) as an organic photocatalyst, the reaction proceeded smoothly in the absence of transition-metal catalysts at ambient temperature, affording the corresponding products, 1,2,4-triaryl 1,2,4-triazolidines, in good to excellent yields. This work demonstrates a new synthetic application of readily available azobenenes and provides a novel strategy for constructing 1,2,4-triazolidines.

A visible-light-mediated protocol for the hydroacylation of azobenzenes with α-keto acids has been developed. In the absence of any catalyst or additive, decarboxylative hydroacylation proceeded smoothly under visible-light irradiation at room temperature. A wide range of azobenzenes and α-keto acids were well-tolerated and afforded hydroacylation products in high to excellent yields. Preliminary investigations indicated that photoactive azobenzenes absorb visible light to enable the transformation.

A visible-light-promoted highly site-selective N1-alkylation of benzotriazoles with diazo compounds has been achieved under mild and metal-free conditions. Using cheap, readily available p-benzoqui...

A lithium chloride catalyzed aza-Michael reaction of pyrazoles to α,β-unsaturated imides has been developed. A range of aromatic and aliphatic α,β-unsaturated imides are found to be suitable for the established method, providing the corresponding aza-Michael adducts in up to 93% yields. The inexpensive catalyst, good substrate tolerance, and ease of scale-up make this procedure highly practical.

The hydrocyanation of 2-arylmethyleneindan-1,3-diones with potassium hexacyanoferrate(II) as a nontoxic cyanating agent to synthesize 2-(1,3-dioxoindan-2-yl)-2-arylacetonitriles in the presence of benzoyl chloride as a promoter and potassium carbonate as a base by a one-pot procedure is described. The use of nontoxic and inexpensive cyanide source, high yield and simple workup procedures are the advantages of this protocol.

Single- or double-oxa-Michael addition of ynones with various alcohols was achieved at room temperature. (E)-3-Alkoxyprop-2-en-1-ones and 3,3-dialkoxypropan-1-ones were efficiently synthesized by time-controlling approach. This protocol has advantages of wide range of substrates, no transition metal catalyst, mild condition, high yield and high stereoselectivity.

Using methanol as a sustainable C1 source, cobalt-catalyzed α-methoxymethylation and α-aminomethylation of ketones have been developed. With cheap CoCl2·6H2O as catalyst and TBHP as oxidant, the methoxymethylated products were obtained within a short reaction time in up to 91% yield. Based on the observed reversibility of methoxy adduct to enone, the α-aminomethylation of ketones was then achieved by a one-pot methylenation/aza-Michael addition sequence. In addition, an easy way to convert α-methoxymethyl ketones to α-aminomethyl ketones has been discovered.

An efficient method for the synthesis of the title compounds by reactions of divinyl ketones with thiourea is described. This protocol has the advantages of high yields, mild reaction conditions and simple work-up procedure.

Visible light, in combination with the molecular iodine catalyst-mediated α-hydroxylation of α-methylene ketones, has been developed. The reaction proceeds smoothly in methanol at room temperature under aerobic conditions and shows exclusive selectivity toward methylene ketones. Mechanistic studies have revealed that the reaction proceeds by a radical pathway. Renewable energy, metal-free catalyst and abundant oxygen source alongside a wide scope and novel selectivity are features that make this strategy practical and eco-friendly.

A straight-forward and atom-economical Cu(II)/PBQ-catalyzed oxidative phosphonation of 3,4-dihydro-1,4-benzoxazin-2-ones has been developed through an OEO involving oxidative Pudovik reaction. The experiments are performed under mild reaction conditions to construct new Csp3–P bonds and provide a new opportunity to obtain potentially bioactive α-aminophosphonates with a novel structure.

An efficient method for the synthesis of pyrazolo $$[1{,}5\hbox {-}a]$$ pyrimidines by the tandem reactions of dienones with pyrazole-3-amine through an aza-Michael addition/nucleophilic addition/1,3-hydrogen transfer process in the presence of potassium hydroxide is described. This protocol offers access to 7-arylethyl-5-arylpyrazolo $$[1{,}5\hbox {-}a]$$ pyrimidines in good to excellent yield. Meanwhile for 4-substituted dienones, different products, 7-arylethylene-5-arylpyrazolo $$[1{,}5\hbox {-}a]$$ pyrimidines, are given through an aza-Michael addition/nucleophilic addition/oxidation process. A gram-scale reaction has been performed to demonstrate the potency of optimized procedure for the scale-up process. SYNOPSIS7-Arylethyl-5-arylpyrazolo $$[1{,}5\hbox {-}a]$$ pyrimidines were efficiently synthesized by the reactions of 4-unsubstituted dienones with pyrazole-3-amine. In contrast, 7-arylethylene-5-arylpyrazolo $$[1{,}5\hbox {-}a]$$ pyrimidines could be afforded by the reactions of 4-substituted dienones with pyrazole-3-amine.

Catalyst-free sulfa-Michael addition of pyrimidine-2-thiol to nitroolefins is described. A series of 2-((2-nitro-1-arylethyl)thio)pyrimidines were efficiently synthesized. The protocol has advantages of wide range of substituents tolerance, no catalyst, additives and bases, mild condition, and high yield. The method can also extend to gram scale.

The mono-aza-Michael additions of divinyl ketones with benzotriazole and other N-heterocycles in the presence of cesium carbonate were described. This protocol has advantages of high regioselectivity, high yield, and mild condition.

The regioselective 1,4-conjugate aza-Michael addition of dienones with benzotriazole catalyzed by potassium acetate is described. A series of 3-(benzotriazol-1-yl)-1,5-diarylpent-4-en-1-ones were efficiently synthesized under mild conditions. This protocol has advantages of transition-metal free catalyst, high yield and high regioselectivity.

Seventeen examples of 2,6-diarylspiro[cyclohexane-1,3′-indoline]-2′4-diones were efficiently prepared by the Cs2CO3-catalysed chemoselective double Michael additions of indolin-2-one to divinyl ketones. This method has the advantage of high chemoselectivity, mild reaction conditions, high yield and atom- and step-economy.

Indole is one of the utmost important heterocycles as it is an essential nucleus of many pharmaceutical compounds. Its aza-Michael reaction, however, is underdeveloped because of the moiety’s inherent characteristics. Here, a potassium hydroxide catalysed intermolecular aza-Michael reaction of 3-cyanoindole with aromatic enones is described. A variety of chalcone derivatives are well tolerated and afford the corresponding N-adducts in moderate to high yields. The use of a cheap catalyst, low catalyst loading, mild reaction temperature, and good substrate tolerance make this procedure a direct and facile method for the preparation of N1-functionalized indoles.

The selective monohydrocyanation of diimines using potassium hexacyanoferrate(II)-benzoyl chloride reagent system as a cyanide source under catalyst-free condition is described. The advantages of this protocol are the non-toxic, non-volatile and inexpensive cyanide source, high yield, and simple work-up procedure.

Saturated six-membered rings were constructed directly using calcium carbide as an acetylene source by one-step procedure, and functionalized cyclohexanes, 1,3,5-triaroylcyclohexanes, were efficiently synthesized by reactions of calcium carbide with aromatic or heteroaromatic aldehydes in high yield. This protocol has the advantages of using inexpensive and renewable resource, no flammable and explosive gas and no transition-metal catalysts.

1 H -Indazoles are important heterocycles as they are a substantial part in many drugs. Here, a DBU-catalyzed aza-Michael reaction of indazole with enones is described. A variety of aromatic and aliphatic enones are well tolerated and afford the corresponding N 1 -substituted 1 H -indazoles in high to excellent yields with exclusive N 1 -regioselectivity. The use of a metal-free catalyst, good substrate tolerance, mild reaction conditions, and high atom economy make this procedure a direct and facile method for the preparation of N 1 -substituted 1 H -indazoles.

Using an efficient aerobic oxidative method, the synthesis of ten 3,5-disubstituted isoxazoles by treatment of α,β-unsaturated ketones with hydroxylamine and NaOH at room temperature has been achieved.

CeCl3·7H2O–NaI/SiO2 system promoted Beckmann rearrangement of a variety of aldoximes and ketoximes was efficiently conducted under solvent-free and microwave irradiation conditions. This protocol afforded an alternative method for the preparation of amides by Beckmann rearrangement with advantages of short reaction time, high yield, no pollution, simple operation and easy work-up.

Poly(ethylene glycol) (PEG) supported dichlorophosphate was efficiently used as a recoverable new dehydration reagent for rapid synthesis of 2-amino-5-substituted-1,3,4-thiadiazoles under microwave irradiation and solvent-free condition by reactions of thiosemicarbazide with aliphatic acids, benzoic acid, aryloxyacetic acids or furan-2-carboxylic acids.

As one of the most important methods to construct C—C bond in enantioselective manner and afford optically active β-cyano compounds, catalytic asymmetric conjugate cyanation reaction has attracted much attentions worldwide since the first report in 2003. Over the past decade, some important achievements have been made in the catalytic asymmetric conjugate cyanation of α,β-unsaturated imides, α,β-unsaturated N-acylpyrroles, α,β-unsaturated ketones, α,β-unsaturated esters, and nitroalkenes. The research progress in this field is reviewed from both metal catalysis and organocatalysis based on different Michael acceptors.