Synthesis of 4-(Iso)Quinolinyl-3(2H )-furanones from (Iso)Quinoline N -oxides and 1,4-Diyn-3-ones: A Comparison of Copper Catalysis and Metal-free Reaction

Synthesis of 3(2H)-furanone derivatives: p-TsOH/halotrimethylsilane promoted cycloketonization of γ-hydroxyl ynones

A p-TsOH/halotrimethylsilane facilitated cycloketonization of γ-hydroxyl ynones is detailed. This methodology enables the one-step synthesis of polysubstituted 3(2H)-furanone products. It is remarkable that the reaction exhibits excellent regio- and chemoselectivity by the addition of very small quantities of p-toluenesulfonic acid and water.

Direct Two Carbon Ring Expansion of 1-Indanones with Ynones: An Eco-Friendly, One-Flask Approach to Functionally Enriched 5H-Benzo[7]annulenes

Direct 2C-ring expansion of 1-indanones with ynones to 5H-benzo[7]annulenes has been observed, and its generality has been gauged (19 examples). Overall, this simple and convenient cascade process to 5H-benzo[7]annulenes involves engagement of 1-indanone with two ynone moieties with formation of three new C-C σ-bonds, cleavage of C-C σ-bond, and concurrent functionality amplification. The resulting seven-membered ring, laced with an opportunistic disposition of four proximal functional groups, offers avenues for their further productive interplay. Our new approach embraces many green and eco-friendly features.

Indeno-Annulation of o-Formyl-Ynones, o-Bis-Ynones, and p-Bis-o-Formyl-Ynones with Dimethyl Acetone-1,3-Dicarboxylate: One Flask Cascade Synthesis of Functionally Endowed 9-Fluorenols and Indeno[1,2-b]fluorenols

A mild, scalable, one-pot access to multifunctional 9-fluorenols from o-formyl-ynones and o-bis-ynones on reaction with dimethylacetone-1,3-dicarboxyate through tandem Michael addition-Aldol condensation cascade has been conceptualized and executed. The scope and utility of this synthetic approach have been further amplified for one-pot entry into functionally enhanced, higher order fluorenols like pentacyclic indeno[1,2-b]fluorene-6,12-diols and further to indeno[1,2-b]fluorene-6,12-diones through the implementation of "double indeno-annulation" tactic on p-bis-o-formyl ynones and dimethylacetone-1,3-dicarboxylate. Besides several green attributes, the current approach is also compatible with the emerging time and energy economy features and is a swift gateway to build complexity.

One-Pot Synthesis of Functionally Enriched Benzo[b]fluorenones: An Eco-Friendly Embedment of Diverse 1-Indanones into o-Bis-Ynones

An efficient, base-promoted, one-pot, metal-free, open-flask synthesis of diverse, functionally enriched benzo[b]fluoren-11-ones has been discovered, and wide applicability of this exceptionally simple protocol with green flavors has been scoped. This synthesis proceeds via an unanticipated, tandem, double-aldol condensation between in situ-generated 1-indanone dianions and o-bis-ynones to furnish benzo[b]fluoren-11-ones harboring as many as six variegated substituents on their tetracyclic framework. This methodology has also been amplified to access heterocyclic analogues 2- and 4-azabenzo[b]fluorenones of benzo[b]fluoren-11-ones and extended to mixed linear-angular annulated pentacyclic dibenzo[a,h]fluoren-13-one.

In Situ-Generated Ammonia Mediates Deep Restructuring of o-Bis-Ynones through a Cascade Process: One-Pot Synthesis of 2-Azafluorenones

One-pot synthesis of 2-azaflorenones from readily accessed o-bis-ynones through Michael addition, orthogonal aldol reaction, dehydrative isomerization, and a 6-endo-dig-cyclization cascade, triggered by in situ-generated ammonia in the presence of a Cu(I) catalyst, has been discovered and its generality scoped. A few selected reactions of a prototypical 2-azafluorenone have been explored for functionality augmentation in its core structure. Overall, this operationally convenient 2-azafluorenone synthesis involves the formation of five new bonds (3 C-N and 2 C-C) in one pot and embodies many green and sustainable features; notably, the reagent ammonia is subsumed into the reactant o-bis-ynones with atom economy, and the only by-product is water.

Recursive Anion-Triggered Tandem Reactions of ortho-Bis-ynones: Tunable Synthesis of 1-Indenones and Cyclopenta[a]inden-8(2H)-ones

Recursive anion-mediated activation of o-bis-ynones sets off a Michael addition-aldol reaction-dehydrative rearrangement cascade, leading to the one-pot synthesis of 1-indenones via orthogonal interplay between the two ortho-ynone moieties. Repeating the recursive anion engagement with the 1-indenones unfolded access to a functionally embellished cyclopenta[a]inden-8(2H)-one core and its spiroannulated analogues either directly or stepwise through tandem 1,6-Michael-type addition-6π electrocyclization and an in situ oxidation sequence.

Tandem Michael-anti-Michael Addition-Mediated Orthogonal Strapping of Diynones: Regioselective Spirocyclopentannulation of Oxindoles and Pyrazolones and DFT Validation

An efficient protocol involving the transformation of sequentially generated recursive anions from heterocyclic precursors to orthogonally strap diynones through one pot transition-metal-free spirocyclopentannulation has been devised, employing oxindoles and pyrazolones as prototypical platforms. Insights into these regioselective tandem Michael-anti-Michael processes have been gleaned through DFT calculations.

Phosphine-Catalyzed Synthesis of 3-Allyl-4-pyrones by the Tandem Reaction of Diynones and Allylic Alcohols

A simple and effective tandem reaction of diynones and allylic alcohols was developed to afford functionalized 3-allyl-4-pyrones in moderate to excellent yields. This protocol underwent a Michael addition─Claisen rearrangement─O-cyclization process, which exhibited broad substrate tolerance, high regioselectivity, and atom economy under a metal-free condition. Moreover, functional transformation of the products was also further studied.

Recent Progress in Enolonium Chemistry under Metal-Free Conditions

Umpolung approach through inversion of the polarity of conventional enolates, has opened up an unprecedented opportunity in the cross-coupling via alkylation. The enolonium equivalents can be accessed either by hypervalent iodine reagents, activation/oxidation of amides, or the oxidation of alkynes. Under umpolung conditions, highly basic conditions required for classical enolate chemistry can be avoided, and they can couple with unmodified nucleophiles such as heteroatom donors and electron-rich arenes.

Catalyst- and Additive-Free Annulation of Ynediones and (Iso)Quinoline N-Oxides: An Approach to Synthesis of Pyrrolo[2,1-a]Isoquinolines and Pyrrolo[1,2-a]Quinolines

A simple and effective annulation of ynediones and (iso)quinoline N-oxides was developed to afford various functionalized pyrrolo[2,1-a]isoquinolines and pyrrolo[1,2-a]quinolines in moderate to excellent yields. This protocol underwent a tandem [3 + 2] cycloaddition/ring-opening/N-nucleophilic addition, which exhibited high regioselectivity, broad substrate tolerance, and atom economy under catalyst-, additive-free, and air conditions. Moreover, indolizine was also successfully prepared using pyridine N-oxide.

Regiodivergent Hydration-Cyclization of Diynones under Gold Catalysis

Skipped diynones, efficiently prepared from biomass-derived ethyl lactate, undergo a tandem hydration-oxacyclization reaction under gold(I) catalysis. Reaction conditions have been developed for a switchable process that allows selective access to 4-pyrones or 3(2H)-furanones from the same starting diynones. Further application of this methodology in the total synthesis of polyporapyranone B was demonstrated.

Palladium-Catalyzed Multicomponent Synthesis of Fully Substituted Alkylidene Furanones

In the presence of a catalytic amount of Pd(OAc)₂ and XantPhos, the three-component reaction of ynones, imines, and aryl iodides affords fully substituted alkylidene-furan-3(2H)-ones via a sequence of the Mannich reaction followed by chemo- and regioselective oxypalladation and reductive elimination. One carbon-oxygen and two carbon-carbon bonds are generated to afford the heterocycle in good to excellent yield.

Solvent-controlled divergent annulation of ynones and (iso)quinoline N-oxides: of 3-((iso)quinolin-1-yl)-4H-chromen-4-ones and 13H-isoquinolino[2,1-a]quinolin-13-ones

An effective annulation of ynones and (iso)quinoline N-oxides was developed to deliver various functionalized 3-((iso)quinolin-1-yl)-4H-chromen-4-ones and 13H-isoquinolino[2,1-a]quinolin-13-ones in moderate to excellent yields, respectively. This protocol exhibits high regioselectivity and broad substrate scope under transition-metal-free conditions. Moreover, the key reaction intermediate was successfully isolated and determined unambiguously by single crystal X-ray crystallography.

Synthesis of 3-(2-quinolyl) chromones from ynones and quinoline N-oxides via tandem reactions under transition metal- and additive-free conditions

The synthesis of 3-(2-quinolyl) chromones from ynones and quinoline N-oxides via a sequential [3+2] cycloaddition/ring-opening/O-arylation reaction under transition metal- and additive-free conditions is reported.