Synthesis of 3‐Iodoquinolines by Copper‐Catalyzed Tandem Annulation from Diaryliodoniums,Nitriles, and 1‐Iodoalkynes

A novel method for the synthesis of 3‐iodoquinolines was developed by copper‐catalyzed tandem annulation from diaryliodoniums, nitriles, and 1‐iodoalkynes. It is a method that is characterized by the most convenient operation and wide molecular diversity.

     

Catalytic Asymmetric Synthesis of 2‐Alkyleneoxetanes through [2+2] Annulation of Allenoates with Trifluoromethyl Ketones

The first example of a β‐isocupreidine (β‐ICD)‐catalyzed highly enantioselective [2+2] annulation of allenoates with trifluoromethyl ketones has been disclosed, allowing the synthesis of optically active 2‐alkyleneoxetanes in moderate to good yields along with good to high enantioselectivities and high diastereoselectivities. Further transformations of the cycloadducts have been also disclosed to afford biologically interesting 6‐trifluoromethyl‐5,6‐dihydropyran‐2‐ones and trifluoromethyl β‐keto acids in good yields.     

Phosphine‐Catalyzed [3+2] and [4+3] Annulation Reactions of C,N‐Cyclic Azomethine Imines with Allenoates

Phosphine‐catalyzed [3+2] and [4+3] annulation reactions of C,N‐cyclic azomethine imines with allenoates have been developed to give a variety of pharmaceutically attractive tetrahydroisoquinoline derivatives in moderate to excellent yields. The two distinct reaction pathways, [3+2] and [4+3] cyclization, depend on the nature of the nucleophilic phosphine and the allenoate. Generally, for α‐alkylallenoates, the reactions always proceed with [3+2] cyclization as the major pathway no matter what phosphine was used; for α‐ArCH₂‐substituted allenoates, the reaction pathway was controlled by the phosphine catalyst used.     

tert‐Butoxide‐Mediated Arylation of 2‐Substituted Cyanoacetates with Diaryliodonium Salts

A transition metal‐free direct arylation of 2‐substituted cyanoacetates with diaryliodonium salts was developed. With this approach, a wide range of α‐tolunitrile derivatives has been synthesized in good to excellent yields of 45–92%. Furthermore, the practicability of this approach is further manifested in the synthesis of a related bioactive agent of glutarimide.

     

Sulfur‐Assisted and 1,8‐Diazabicyclo[5.4.0]undec‐7‐ene (DBU)‐Catalyzed Cyclization of 2‐Alkynylanilines for the Metal‐Free Synthesis of Indole Derivatives

A sulfur‐assisted and 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU)‐catalyzed cyclization of 2‐alkynylanilines for the metal‐free synthesis of indole derivatives is reported. As a result of the metal‐free process, the ready availability of the starting materials and the simple and convenient operation, the type of reaction presented here has potential utility in organic synthesis. A 10‐gram scale preparation may demonstrate the possibility of its application in the environmentally friendly synthesis of indole derivatives.     

Potassium Hydroxide/Dimethyl Sulfoxide Superbase‐Promoted Transition Metal‐Free Synthesis of 2‐Substituted Benzothiophenes under Visible Light

A potassium hydroxide/dimethyl sulfoxide (KOH/DMSO) superbase‐promoted method for the synthesis of 2‐substituted benzothiophenes has been developed via photoinduced intermolecular annulation of 2‐halothioanisoles with terminal alkynes at ambient temperature. The present protocol uses commercially available 2‐halothioanisoles as substrates and visible light as energy force, which offers a wide range of benzothiophenes regioselectively in moderate to good yields. Such a facile and effective transformation will provide an environment‐friendly approach to the synthesis of benzothiophene derivatives.

     

Potassium tert‐Butoxide‐Promoted Synthesis of 1‐Aminoisoquinolines from 2‐Methylbenzonitriles and Benzonitriles under Catalyst‐Free Conditions

Herein a practical and efficient protocol for preparing a range of aminoisoquinolines is reported. Various aminoisoquinolines were prepared in moderate to good yields from the corresponding 2‐methylbenzonitriles and benzonitriles upon treatment with potassium tert‐butoxide.

     

Transition Metal‐Free Approach to Propynenitriles and 3‐Chloropropenenitriles

A transition metal‐free, facile and efficient one‐pot protocol for the synthesis of propynenitriles from readily available 3‐chloropropenals is disclosed. The reaction conditions have also been optimized for the exclusive formation and isolation of 3‐chloropropenenitriles which are important building blocks in general and are intermediates in the synthesis of propynenitriles. The hallmark of the methodology is the use of non‐toxic reagents, milder, metal‐free and economically benign reaction conditions avoiding a harsh dehydration step while achieving excellent yields.

     

Visible Light‐Mediated Metal‐Free Synthesis of Vinyl Sulfones from Aryl Sulfinates

Visible light and eosin Y catalyze the synthesis of vinyl sulfones from aryl sulfinates and alkenes by a photoredox process. The reaction scope is broad in aryl sulfinates and alkenes and the general and simple procedure provides a metal‐free alternative for the synthesis of synthetically valuable vinyl sulfones.

     

Gold‐Catalyzed Synthesis of Bicyclo[3.2.0]heptenes via a Formal [3+2]/[2+2]‐Annulation of Allylsilane with 4‐Methoxybut‐2‐yn‐1‐ols

This work reports the novel gold‐catalyzed [3+2]/[2+2]‐annulation of allylsilane with 4‐methoxybut‐2‐yn‐1‐ols that yields highly strained bicyclo[3.2.0]heptene products efficiently and stereoselectively.     

Phenanthrene Synthesis by Eosin Y‐Catalyzed,Visible Light‐ Induced [4+2] Benzannulation of Biaryldiazonium Salts with Alkynes

A metal‐free, visible light‐induced [4+2] benzannulation of biaryldiazonium salts with alkynes was developed. With eosin Y as photoredox catalyst, a variety of 9‐substituted or 9,10‐disubstituted phenanthrenes were obtained via a cascade radical addition and cyclization sequence.     

Aldehyde‐Catalyzed Transition Metal‐Free Dehydrative β‐Alkylation of Methyl Carbinols with Alcohols

Different to the borrowing hydrogen strategy in which alcohols were activated by transition metal‐catalyzed anaerobic dehydrogenation, the direct addition of aldehydes was found to be an effective but simpler way of alcohol activation that can lead to efficient and green aldehyde‐catalyzed transition metal‐free dehydrative C‐alkylation of methyl carbinols with alcohols. Mechanistic studies revealed that the reaction proceeds via in situ formation of ketones by Oppenauer oxidation of the methyl carbinols by external aldehydes, aldol condensation, and Meerwein–Ponndorf–Verley (MPV)‐type reduction of α,β‐unsatutated ketones by substrate alcohols, affording the useful long chain alcohols and generating aldehydes and ketones as the by‐products that will be recovered in the next condensation to finish the catalytic cycle.     

Stereocontrolled [4+1] Annulation of α‐Hydroxycyclobutenones: Synthesis of Polysubstituted Cyclopentenones

A stereocontrolled [4+1] annulation of α‐hydroxycyclobutenones has been disclosed. For the first time, α‐hydroxycyclobutenones have been proven as facile diene precursors for [4+1] annulation. Meanwhile, the reported transformation presents a concise synthetic route to polysubstituted cyclopentenones with high stereoselectivity.

     

Metal‐Free Catalytic Hydrogenation of Imines with Recyclable [2.2]Paracyclophane‐Derived Frustrated Lewis Pairs Catalysts

A series of [2.2]paracyclophane‐derived frustrated Lewis pairs (FLPs) with reversible, metal‐free hydrogen activation was synthesized and successfully applied in the hydrogenation of imines in moderate to good yields. The high stability of the novel FLP system enables effective recycling of the metal‐free catalysts. This reaction could also be compatible with a larger scale and developed into a pharmaceutical synthesis of cinacalcet {(R)‐N‐[1‐(1‐naphthyl)ethyl]‐3‐[3‐(trifluoromethyl)phenyl]propan‐1‐amine} without heavy metal residues.

     

Bioinspired,Base‐ and Metal‐Free,Mild Decarboxylative Aldol Activation of Malonic Acid Half Thioesters Under Phase‐Transfer Reaction Conditions

Utilizing ‘off the shelf’ commercially available, cheap, small synthetic molecules that mimic the efficient mediation of important bioreactions utilized by Nature is not only highly sought after but also currently highly topical. This paper details our preliminary efforts at developing a unique base‐ and metal‐free phase‐transfer‐mediated malonic acid thioester (MAHT) ‘activation protocol’ that efficiently generates (±)‐β‐thioesters. Our bioinspired aldol process is exceptionally mild, conducted under near neutral pH reaction conditions, does not require an inert, oxygen‐free atmosphere or anhydrous reaction conditions and is highly atom‐economic. Exemplifying the utility of our protocol, the synthesis of an array of structurally and functionally diverse (±)‐β‐hydroxy thioesters equipped with highly prized functionality, i.e., chlorine, bromine, fluorine, nitrile and nitro groups, is reported, as is the diastereoselective potential of this important reaction.

     

Lewis Acid‐Catalyzed [3+4] Annulation of 2‐(Heteroaryl)‐ cyclopropane‐1,1‐dicarboxylates with Cyclopentadiene

A novel Lewis acid‐catalyzed [3+4] annulation of 2‐(heteroaryl)cyclopropane‐1,1‐dicarboxylates with cyclopentadiene is reported. This reaction proceeds via an electrophilic attack of the Lewis acid‐activated donor‐acceptor cyclopropane onto cyclopentadiene followed by Friedel–Crafts intramolecular alkylation of the heteroarene substituent. This is the first general example of reactions of donor‐acceptor cyclopropanes wherein the donor substituent serves as a nucleophile. The described annulation represents a convenient approach to bicyclo[3.2.1]octa‐2,6‐dienes with heteroarenes annulated to C(2)‐C(3) bond. Its efficiency was demonstrated for a series of furyl, thienyl, pyrrolyl, benzofuryl, benzothienyl, and indolyl substituted cyclopropanes. Additionally, in the case of 2‐(5‐methyl‐2‐furyl)cyclopropane‐1,1‐diester we observed the predominant formation of product of the [3+4] annulation or the tetracyclic 5,8‐methanocyclopenta[a]azulene derivative, depending on the reaction conditions.     

Direct Decarboxylative Alkynylation of α,α‐Difluoroarylacetic Acids under Transition Metal‐Free Conditions

An efficient and generally applicable protocol for decarboxylative coupling of α,α‐difluoroarylacetic acids with ethynylbenziodoxolone (EBX) reagents has been developed, affording α,α‐difluoromethylated alkynes bearing various functional groups in moderate to excellent yields. Remarkably, this potassium persulfate (K₂S₂O₈)‐promoted reaction employs water as solvent under transition metal‐free conditions, thus providing a green synthetic approach to α,α‐difluoromethylated alkynes.

     

Palladium‐Catalyzed Annulation of 2‐(1‐Alkynyl)benzenamines with Disulfides: Synthesis of 3‐Sulfenylindoles

3‐Sulfenylindoles can be efficiently prepared in moderate to good yields from 2‐(1‐alkynyl)benzenamines and disulfides using the palladium/air catalytic systems. The study also provides a useful route to the synthesis of fipronil analogues.     

Enantioselective Synthesis of Highly Functionalized Trifluoromethyl‐Bearing Cyclopentenes: Asymmetric [3+2] Annulation of Morita–Baylis–Hillman Carbonates with Trifluoroethylidenemalonates Catalyzed by Multifunctional Thiourea‐Phosphines

On the basis of the design and synthesis of multifunctional thiourea‐phosphines, a catalytic method for the asymmetric [3+2] annulation of Morita–Baylis–Hillman carbonates with trifluoroethylidenemalonates has been developed, affording highly functionalized trifluoromethyl‐bearing cyclopentenes in excellent yields, high diastereoselectivities and enantioselectivities under mild conditions.     

Regioselective Synthesis of Functionalized Pyrroles via Gold(I)‐Catalyzed [3+2] Cycloaddition of Stabilized Vinyl Diazo Derivatives and Nitriles

The reaction of nitriles with alkenyldiazo compounds in the presence of gold catalysts provides functionalized pyrrole derivatives in moderate to high yields. This formal [3+2] cyclization reaction takes place with complete regioselectivity. The observed regiochemical outcome suggests the attack of the nitrile to the terminal position of the alkenylgold carbenoid (vinylogous reactivity). A broad range of nitriles (including those bearing functional groups) is compatible with this cyclization reaction.