Facile Synthesis of 3a,6a-Dihydro-furo[2,3-b]furans and Polysubstituted Furans Involving Dearomatization of Furan Ring via Electrocyclic Ring-Closure

Calcium-Catalyzed Synthesis of Fused Furo[2,3-b]furans and Substituted Furans from 2-Oxo Aldehydes and Cyclic Enols

We report here an atom-economical, syn-diastereoselective synthesis of naphtho-fused furo[2,3-b]furans along with naphthofurans at room temperature using readily available 2-naphthols and 2-oxo aldehydes using an alkaline earth catalyst [Ca(OTf)2]. 2-Oxo aldehydes having both aryl and alkyl substitutions reacted well. A good number of arenols responded to give fused furans, but selected arenols gave only furofurans. Synthetic applications and gram-scale synthesis were also demonstrated to strengthen this strategy.

Pd-Catalyzed Intermolecular Carbonylative Dearomatization of Arylamines with Propargylic Acetates for Synthesis of Bridged Polycyclic Lactams

A new palladium-catalyzed multicomponent dearomatization of arylamines with CO and propargylic acetates for the synthesis of bridged polycyclic lactams is described. This method allows double annulation at the ipso and para positions of the amino group to form four new bonds, three C-C bonds and one C-N bond. DFT calculations and experimental studies indicate that the efficient formation of the allenecarboxanilide intermediate is the key step to achieve the dearomative transformation.

Ruthenium(ii)-catalysed direct synthesis of mono-allylation products of 1,3-diketones from cinnamyl alcohols

The complex, [Ru(p-cymene)(dppe)Cl]PF6·C7H8 is an efficient catalyst for the direct carbon–carbon bond formation reactions to form enantio- and regioselective mono-allylation products of diketones by cinnamyl alcohol with high yield.

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.

A Base-Mediated Approach Towards Dihydrofuro[2,3-b]Benzofurans from 2-Nitrobenzofurans and 1,3-Dicarbonyls

A straight-forward approach for the synthesis of a dihydrofuro[2,3-b]benzofuran derivatives has been achieved through a base-mediated Michael addition of 1,3-dicarbonyls to 2-nitrobenzofurans followed by intramolecular cyclization. A variety of 1,3-dicarbonyls, including cyclic as well as trifluoromethylated ones, have been subjected to react with 2-nitrobenzofurans under optimal conditions, and the respective dihydrofuro[2,3-b]benzofurans could be accessed in moderate to excellent yields.

Stereoselective synthesis of hexahydrofuro[3,4-b]furan-4-ol and its dimer via tandem Prins and pinacol rearrangement

A novel synthetic route for the cyclization of ((4S,5R)-2,2-dimethyl-5-vinyl-1,3-dioxolan-4-yl)methanol with aldehydes to give hexahydrofuro[3,4-b]furan-4-ol and its dimer was developed. A variety of substituted furanol (up to 86%) and its bis-derivatives were obtained in good yields (up to 66%) with excellent diastereo- and enantio-selectivity mediated by borontrifluoride etherate. The dimer was conveniently converted into its corresponding monomer using aqueous zinc(ii) chloride in THF in quantitative yields.

Pd-catalyzed regioselective intramolecular direct arylation of 3-indolecarboxamides: access to spiro-indoline-3,3′-oxindoles and 5,11-dihydro-6H-indolo[3,2-c]quinolin-6-ones

We report regioselective intramolecular direct C-3 and C-2 arylations of the indole rings of 3-indolecarboxamides for diastereospecific production of spiro-indoline-3,3′-oxindoles and 5,11-dihydro-6H-indolo[3,2-c]quinolin-6-ones, respectively, under different reaction conditions.

Aerobic oxidative α-arylation of furans with boronic acids via Pd(ii)-catalyzed C–C bond cleavage of primary furfuryl alcohols: sustainable access to arylfurans

Aerobic oxidative α-arylation of furans with boronic acids via Pd(ii)-catalyzed C–C bond cleavage of primary furfuryl alcohol provides sustainable access to arylfurans.

Catalytic, Cascade Ring-Opening Benzannulations of 2,3-Dihydrofuran O,O- and N,O-Acetals

An Al(OTf)3 -catalyzed intramolecular cascade ring-opening benzannulation of 2,3-dihydrofuran O,O- and N,O-acetals is described. The cascade sequence involves the dihydrofuran ring-opening by acetal hydrolysis, an intramolecular Prins-type cyclization, and aromatization to generate an array of benzo-fused (hetero)aromatic systems in up to 95 % yield. This method represents the first example of dihydrofuran acetal usage in benzannulation reactions. The approach provides excellent regiocontrol based on the choice of alkenes used to form the requisite dihydrofuran acetals.

Selective Pd-catalyzed α- and β-arylations of the furan rings of (ortho-bromophenyl)furan-2-yl-methanones: C(CO)–C bond cleavage with a furan ring as a leaving group and synthesis of furan-derived fluorenones

Selective palladium diacetate-catalyzed α- and β-arylations of the furan rings of (ortho-bromophenyl)furan-2-yl-methanones 1 under two different conditions are reported.

Palladium-catalyzed dearomatizing 2,5-alkoxyarylation of furan rings: diastereospecific access to spirooxindoles

A protocol for Pd-catalyzed intra- and intermolecular 2,5-alkoxyarylation reactions of furans to diastereospecifically synthesize two series of spirooxindoles is reported.

Access to polysubstituted indoles or benzothiophenes via palladium-catalyzed cross-coupling of furfural tosylhydrazones with 2-iodoanilines or 2-iodothiophenols

Palladium-catalyzed cross-coupling of furfural tosylhydrazones with 2-iodoanilines or 2-iodothiophenols produces polysubstituted indoles or benzothiophenes, respectively.

DDQ-mediated oxidative coupling: an approach to 2,3-dicyanofuran (thiophene)

A facile oxidative coupling of α-carbonyl radicals to 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) for the synthesis of 2,3-dicyanofurans and thiophenes starting from readily available β-diketones, simple ketones, and β-keto thioamides in up to 95% yield in one step was developed. Mechanistic investigations revealed that a radical process could be involved in this transformation, and a water promoted C-C bond cleavage pathway is proposed for the formation of 2,3-dicyanofurans and thiophenes.