Facile synthesis of polysubstituted furans and dihydrofurans via cyclization of bromonitromethane with oxodienes

A one-pot synthesis of 2,3-dihydrobenzofurans, benzofuran-2(3H)-ones, and indoles via a [4 + 1] annulation reaction of ortho-substituted para-quinone methides and bromonitromethane

Under mild and metal-free reaction conditions, a facile one-pot synthesis of oxygen- and nitrogen-containing benzoheterocycles has been achieved through [4 + 1] annulation of para-quinone methides, followed by an oxidation/elimination sequence, efficiently synthesizing functionalized 2,3-dihydrobenzofuran, benzofuran-2(3H)-one, and indole derivatives in moderate to good yields (up to 72%). A novel functional group tolerant oxidative Nef reaction utilizes DDQ without a base.

Three-Component Condensation of β-Ketonitriles, 4-Fluorobenzaldehyde, and Secondary Cyclic Amines

A new three-component condensation of β-ketonitriles, 4-fluorobenzaldehyde, and secondary cyclic amines was developed. A possible reaction mechanism has been proposed including Knoevenagel condensation followed by aromatic nucleophilic substitution. It was found that in the case of 3-oxopropanenitrile bearing the 6-amino-1,3-dimethyluracil moiety, the reaction is not accompanied by fluorine substitution in the Knoevenagel adduct, and the Michael addition of a secondary amine occurs followed by oxidation.

A facile approach to spiro[dihydrofuran-2,3'-oxindoles] via formal [4 + 1] annulation reaction of fused 1H-pyrrole-2,3-diones with diazooxindoles

There has been developed an easy synthetic approach to spiro[dihydrofuran-2,3'-oxindoles] via a highly diastereoselective formal [4 + 1] cycloaddition reaction of [e]-fused 1H-pyrrole-2,3-diones with diazooxindoles. The described novel heterocyclic systems are heteroanalogues of antimicrobial and antibiofilm fungal metabolites. The developed reaction represents the first example of involving 1H-pyrrole-2,3-diones fused at the [e]-side in a [4 + 1] annulation reaction.

A one-pot ring-closure and ring-opening sequence for the cascade synthesis of dihydrofurofurans and functionalized furans

We have developed a simple novel ring-closure and ring-opening pathway using an organo-base system for the synthesis of highly substituted dihydrofurofuran and furan frameworks via a triethylamine-catalyzed one-pot three-component reaction. The protocol involved a Knoevenagel and Michael adduct via Paal-Knorr cyclization with aromatic/aliphatic glyoxal and 2-cyanoacetophenone under mild and heating conditions with excellent yields through a simple filtration method. The merits of this methodology, including the use of easily available feedstocks and an inexpensive catalyst, Gram-scale synthesis, wide functional group tolerance, an open-air reaction setup, and no need for workup and column-chromatography procedures, make the developed methodology a practical way to access dihydrofurofurans and functionalized furans.

One-Pot Tandem Approach to Functionalized 3-Hydroxy-2-furanyl-acrylamides

A novel one-pot tandem process involving Knoevenagel condensation, Michael addition, selective amidation, and Paal-Knorr cyclization to diverse functionalized 3-hydroxy-2-furanyl-acrylamides from simple 2-oxoaldehydes and aroylacetonitriles was presented. Attempts were also made to expand the scope of the reaction to different 2-heteroarylfurans. The packing diagram of the molecules viewed down along the α-axis of the unit cell showed a characteristic intramolecular classical O-H···O hydrogen bond between hydroxyl and carbonyl O atoms leading to self-associated (Z)-2-furanyl-acrylamides.

Mechanistic Studies on the Michael Addition of Amines and Hydrazines To Nitrostyrenes: Nitroalkane Elimination via a Retro-aza-Henry-Type Process

In this article we report on the mechanistic studies of the Michael addition of amines and hydrazines to nitrostyrenes. Under the present conditions, the corresponding N-alkyl/aryl substituted benzyl imines and N-methyl/phenyl substituted benzyl hydrazones were observed via a retro-aza-Henry-type process. By combining organic synthesis and characterization experiments with computational chemistry calculations, we reveal that this reaction proceeds via a protic solvent-mediated mechanism. Experiments in deuterated methanol CD₃OD reveal the synthesis and isolation of the corresponding deuterated intermediated Michael adduct, results that support the proposed slovent-mediated pathway. From the synthetic point of view, the reaction occurs under mild, noncatalytic conditions and can be used as a useful platform to yield the biologically important N-methyl pyrazoles in a one-pot manner, simple starting with the corresponding nitrostyrenes and the methylhydrazine.