Ring-fluorinated isoquinoline and quinoline synthesis: intramolecular cyclization of o-cyano- and o-isocyano-beta,beta-difluorostyrenes

Aza-Heterocyclic Building Blocks with In-Ring CF2 -Fragment

Modern organic chemistry is a titan supporting and reinforcing pharmaceutical, agricultural, food and material science products. Over the past decades, the organic compounds market has been evolving to meet all the research demands. In this regard, medicinal chemistry is especially dependent on available chemical space as subtle tuning of the molecule structure is required to create a drug with relevant physicochemical properties and a remarkable activity profile. The recent rapid evolution of synthetic methodology to deploy fluorine has brought fluorinated compounds to the spotlight of MedChem community. And now unique properties of fluorine still keep fascinating more and more as its justified installation into a molecular framework has a beneficial impact on membrane permeability, lipophilicity, metabolic stability, pharmacokinetic properties, conformation, pKa , etc. The backward influence of medicinal chemistry on organic synthesis has also changed the landscape of the latter towards new fluorinated topologies as well. Such complex relationships create a flexible and ever-changing ecosystem. Given that MedChem investigations strongly lean on the ability to reach suitable building blocks and the existence of reliable synthetic methods in this review we collected advances in the chemistry of respectful, but still enigmatic gem-difluorinated aza-heterocyclic building blocks.

Morpholine-mediated defluorinative cycloaddition of gem-difluoroalkenes and organic azides

Here, we report the first transition-metal-free defluorinative cycloaddition of gem-difluoroalkenes with organic azides in morpholine as a solvent to construct fully decorated morpholine-substituted 1,2,3-triazoles. Mechanistic studies revealed the formation of an addition-elimination intermediate of morpholine and gem-difluoroalkenes prior to the triazolization reaction via two plausible pathways. Attractive elements include the regioselective and straightforward direct synthesis of fully substituted 1,2,3-triazoles, which are otherwise difficult to access, from readily available starting materials.

Photoredox-Catalyzed gem-Difluoromethylenation of Aliphatic Alcohols with 1,1-Difluoroalkenes to Access α,α-Difluoromethylene Ethers

A switchable synthesis of alcohols and ketones bearing a CF2-OR scaffold using visible-light promotion is described. The method of PDI catalysis is characterized by its ease of operation, broad substrate scopes, and the ability to switch between desired products without the need for transition metal catalysts. The addition or absence of a base plays a key role in controlling the synthesis of the major desired products.

Aluminum-catalyzed tunable halodefluorination of trifluoromethyl- and difluoroalkyl-substituted olefins

Herein, we report unprecedented aluminum-catalyzed halodefluorination reactions of trifluoromethyl- and difluoroalkyl-substituted olefins with bromo- or chlorotrimethylsilane. The interesting feature of these reactions is that one, two, or three fluorine atoms can be selectively replaced with bromine or chlorine atoms by modification of the reaction conditions. The generated products can undergo a variety of subsequent transformations, thus constituting a valuable stock of building blocks for installing fluorine-containing olefin motifs in other molecules.

Aluminum-catalyzed halodefluorination reactions of fluoroalkyl-substituted olefins are developed. The reactions can selectively deliver mono-, di-, or trisubstituted products.

Rhodium/copper-cocatalyzed coupling-cyclization of o-alkenyl arylisocyanides with vinyl azides: one-pot synthesis of α-carbolines

A novel rhodium/copper-cocatalyzed coupling–cyclization reaction of o-alkenyl arylisocyanides with vinyl azides has been developed. The reaction provides a new route to α-carbolines by the formation of two C–C bonds, one C–N bond and two aromatic rings in a single step.

Transition-Metal-Free One-Pot Tandem Synthesis of 3-Ketoisoquinolines from Aldehydes and Phenacyl Azides

An efficient and transition-metal-free strategy for the synthesis of 3-keto-isoquinolines in one pot has been developed from the easily accessible 2-(formylphenyl)acrylates and phenacyl azides. Various substituted aldehydes and phenacyl azides were successfully employed in this transformation to furnish a variety 3-keto-isoquinolines in very good yields. A number of controlled experiments were conducted to postulate the reaction mechanism. Secondary functionalizations of 2-keto-isoquinolins were also performed to showcase the synthetic utility.

Formal [1 + 2 + 3] Annulation: Domino Access to Carbazoles and Indolocarbazole Alkaloids

A new formal [1 + 2 + 3] annulation of o-alkenyl arylisocyanides with α, β-unsaturated ketones under metal-, base-, and acid-free conditions is disclosed. This domino reaction provides a general protocol for the efficient and practical synthesis of a wide range of carbazole derivatives from readily available starting materials in a single operation. Furthermore, this methodology was used as the key step in a protecting-group-free synthesis of indolocarbazole alkaloids arcyriaflavin A and racemosin B.

To each his own: isonitriles for all flavors. Functionalized isocyanides as valuable tools in organic synthesis

The term functionalized isocyanides refers to all those isocyanides in which a neighbouring functional group can finely tune the reactivity of the isocyano group or can be exploited in post-functionalization processes. In this manuscript, we have reviewed all the isocyanides in which the pendant functional group causes either deviation from or reinforces the normal reactivity of the isocyano group and categorized them to highlight their common features and differences. An analysis of their synthetic potential and the possible unexplored directions for future research studies is also addressed.

NaOH-promoted reaction of 1,1-dihaloalkenes and 1H-azoles: synthesis of dihetaryl substituted alkenes

We have developed a useful and simple process for the NaOH-promoted reaction of 1,1-dihaloalkenes and 1H-azoles to afford dipyrazolyl alkenes under mild and transition-metal-free conditions.

Divergent synthesis from reactions of 2-trifluoromethyl-1,3-conjugated enynes with N-acetylated 2-aminomalonates

Divergent synthesis of fluorinated heterocycles from the reactions of 2-trifluoromethyl-1,3-conjugated enynes with N-acetylated 2-aminomalonates and subsequent gold-catalysed cyclization were developed.

New one-pot synthesis of N-fused isoquinoline derivatives by palladium-catalyzed C-H arylation: potent inhibitors of nucleotide pyrophosphatase-1 and -3

Various N-fused isoquinoline derivatives were synthesized using a new one-pot reaction of 1-bromo-2-(2,2-difluorovinyl)benzenes with N-H group containing heterocycles followed by intramolecular palladium-catalyzed C-H arylation. The method described gives convenient access to diverse structures of N-fused polycyclic isoquinolines. Sixteen of the synthesized compounds were screened as potential human nucleotide pyrophosphatase/phosphodiesterase 1 and 3 (h-NPP-1 and h-NPP-3) inhibitors. The most effective h-NPP-1 inhibitor showed an IC₅₀ value as high as 0.36 ± 0.06 μM, whereas the most potent h-NPP-3 inhibitor posessed an inhibitory value of 0.48 ± 0.01 μM. Kinetic and molecular docking studies of both most effective inhibitors were carried out.

Synthesis of 2-fluoro-2-pyrrolines via tandem reaction of α-trifluoromethyl-α,β-unsaturated carbonyl compounds with N-tosylated 2-aminomalonates

A simple base-mediated synthesis of synthetically valuable 2-fluoro-2-pyrrolines from α-trifluoromethyl-α,β-unsaturated carbonyl compounds and N-tosylated 2-aminomalonates was developed.

Cyclization of sulfide, ether or tertiary amine-tethered N-sulfonyl-1,2,3-triazoles: a facile synthetic protocol for 3-substituted isoquinolines or dihydroisoquinolines

A novel cyclization reaction of sulfide, ether or tertiary amine-tethered N-sulfonyl-1,2,3-triazoles, has been developed, efficiently affording 3-substituted isoquinoline or dihydroisoquinoline derivatives.

Synthesis of N-(α-fluorovinyl)azoles by the reaction of difluoroalkenes with azoles

A mild and versatile method for the construction of C-N bonds by the reaction of (2,2-difluorovinyl)arenes with various N-H-containing heterocycles in the presence of K3PO4 has been developed. The reaction proceeded efficiently at room temperature (25 °C) affording the (E)-N-α-fluorovinyl derivatives of azoles 3 in good to excellent yields with relatively high stereoselectivity.

Highly selective introduction of heteroatom groups to isocyanides and its application to electrocyclic reactions

Photoinduced cyclization of o-alkenylaryl isocyanides with (PhS)2 in the presence of (PhTe)2 affords the corresponding bisthiolated indene derivatives in good yields via radical cyclization process by thio radical. The procedure can be applied to the construction of tetracyclic systems by using bis(o-aminophenyl) disulfides in place of (PhS)2. In sharp contrast, when o-alkynylaryl isocyanides are employed as the substrates, novel electrocyclic reactions take place upon photoirradiation or heating at 40~80 °C to generate quinoline 2,4-biradical species, which are trapped with organic diselenides, ditellurides, and molecular iodine to give the corresponding 2,4-diseleno-, ditelluro-, and diiodo-quinoline derivatives, respectively, in good yields. The obtained quinoline derivatives are useful synthetic intermediates; for example, cross-coupling reactions using 2,4-diiodoquinolines lead to the preparation of functionalized quinoline derivatives.

Isocyanides in the synthesis of nitrogen heterocycles

Isocyanides have long proved themselves to be irreplaceable building blocks in modern organic chemistry. The unique features of the isocyano group make isocyanides particularly useful for the synthesis of a number of important classes of nitrogen heterocycles, such as pyrroles, indoles, and quinolines. Several cocyclizations of isocyanides via zwitterions and radical intermediates as well as transition-metal-catalyzed syntheses of different types of heterocycles have recently been developed. Methods starting from isocyanides often have distinct advantages over alternative approaches to the same heterocycles because of their enhanced convergence, the great simplicity of most of the operations with them, and the great variety of isocyanides readily available for use. Isocyanides have also been used in some enantioselective syntheses of chiral heterocyclic compounds, including natural products as well as precursors thereof.