Rhodium‐Catalyzed Cross‐Cyclotrimerization and Dimerization of Allenes with Alkynes

It has been established that a cationic rhodium(I)/binap complex catalyzes the cross‐cyclotrimerization of two molecules of a monosubstituted allene with one molecule of a functionalized alkyne to give 3,6‐dialkylidenecyclohex‐1‐enes. In contrast, the reactions involving di‐ or trisubstituted allenes and/or unfunctionalized alkynes afforded cross‐dimerization products, substituted dendralenes, through β‐hydrogen elimination from the corresponding rhodacycles.     

Concise Synthesis of Dimethyl (2-Oxopropyl)phosphonate and Homologation of Aldehydes to Alkynes in a Tandem Process

The synthesis of dimethyl (diazomethyl)phosphonate, a useful reagent for the homologation of aldehydes to alkynes, is described as a one-pot process and comprises the generation of the azide transfer agent, diazotransfer to dimethyl (2-oxopropyl)phosphonate, and methanolysis, followed by a simple extraction protocol. Previously described syntheses for this bulk product are much more elaborate. The homologation of aldehydes to alkynes can also be extended to a single-step process by adding the aldehyde directly to the reaction mixture prior to isolation of the reagent. The homologation process using dimethyl (diazomethyl)phosphonate was shown to proceed also in nonprotic solvents with mild bases, emphasizing the importance of a facile access to the reagent. The oxidation of alcohols to the required aldehydes was performed by a TEMPO-mediated process using chloramine-T as electron acceptor.     

Superbase-Catalyzed Steric-Hindrance-Induced Dimerization of Alkynones to Highly Functionalized Furans

The cascade dimerization of alkynones bearing sterically hindered secondary alkyl groups at the carbonyl function has unexpectedly furnished highly functionalized furans. The reaction efficiently occurs in the presence of potassium tert-butoxide/dimethylsulfoxide superbase catalytic system at room temperature. Alkynones having additional C−H active site at the carbon-carbon triple bond have followed another dimerization pathway to afford 3-alkenylpyran-4-ones. The discovery of these reactions expands the traditional knowledge about the reactivity of alkynones in strong basic medium.     

Asymmetric Cyclizative Dimerization of (ortho-Alkynyl Phenyl) (Methoxymethyl) Sulfides with Palladium(II) Bisoxazoline Catalyst

The first example of an asymmetric cyclization–dimerization of (ortho-alkynyl phenyl) (methoxymethyl) sulfides with a palladium(II) bisoxazoline (box) catalyst has been developed. The box ligand enhances the alkynophilicity of benzothienyl palladium(II) intermediate A and thus promotes coordination of the second alkyne substrate, leading to the dimerization. The characteristic properties of the box ligand were supported by density functional theory (DFT) calculations of the intermediate. Axially chiral bibenzothiophenes were obtained in good yields with good enantioselectivities.     

Layered Electron Acceptors by Dimerization of Acenes End‐ Capped with 1,2,5‐Thiadiazoles

Layered electron acceptors D1 – 4 equipped with terminal 1,2,5‐thiadiazole groups have been constructed using a one‐pot protocol of acene dimerization. Their molecular structures are determined using single‐crystal X‐ray diffraction analysis. Photophysical and electrochemical properties of these molecules present a marked dependence on conjugation length and molecular geometry. An aggregation‐induced emission peak and an intramolecular excimer emission (IEE) band were observed for D2 and D4 , respectively. This work paves the way for the efficient synthesis of layered heteroacenes.     

Rhodium catalyzed regioselective arene homologation of aryl urea via double C–H bond activation and migratory insertion of alkyne

A convenient rhodium catalyzed oxidative arene homologation of aniline derivatives with symmetrical or unsymmetrical alkynes using Cu(OAc)_2 as oxidant is described. Urea group is shown to be effective as a directing group for initial ortho C–H activation. Two migratory insertion events of alkyne into Rh–C bond occur successively, both with complete regioselectivity. This method is particularly useful for synthesis of polyarenes with different substituents, which has not been reported with conventional protocol. A mechanism has been proposed to explain the observed data.     

Cobalt‐Catalyzed E‐Selective Cross‐Dimerization of Terminal Alkynes: A Mechanism Involving Cobalt(0/II) Redox Cycles

A highly E‐selective cross‐dimerization of terminal alkynes with either terminal silylacetylenes, tert‐butylacetylene, or 1‐trimethylsilyloxy‐1,1‐diphenyl‐2‐propyne in the presence of a dichlorocobalt(II) complex bearing a sterically demanding 2,9‐bis(2,4,6‐triisopropylphenyl)‐1,10‐phenanthroline, activated with two equivalents of EtMgBr, gives a variety of (E)‐1,3‐enynes. A well‐characterized diolefin/cobalt(0) complex, with divinyltetramethyldisiloxane, acted as a catalytically active species without any activation, clearly indicating that a cobalt(0) species is involved in the catalytic cycle.     

Nickel‐Catalyzed Cyclization of ortho‐Iodoketoximes and ortho‐Iodoketimines with Alkynes: Synthesis of Highly Substituted Isoquinolines and Isoquinolinium Salts

A convenient method for the synthesis of highly substituted isoquinolines and isoquinolinium salts by the nickel‐catalyzed cyclization of ortho‐haloketoximes and ‐ketimines, respectively, with alkynes is described. The reaction of ortho‐haloketoximes and various alkynes in the presence of [Ni(PPh₃)₂Br₂] and zinc powder in a mixture of acetonitrile and tetrahydrofuran at 80 °C for 15 hours gave 1,3,4‐trisubstituted isoquinoline products in moderate to excellent yields and high regioselectivity. The corresponding isoquinoline N‐oxide was found to be the intermediate in the cyclization reaction pathway. In contrast, the reaction of ortho‐haloketimines and alkynes under similar catalytic conditions in tetrahydrofuran at 70 °C for two hours gave 1,2,3,4‐tetrasubstituted isoquinolinium salts in good to excellent yields.     

Lithium Halomethylcarbenoids: Preparation and Use in the Homologation of Carbon Electrophiles

α‐Halomethyllithium carbenoids are useful homologating reagents which – reacting under proper reaction conditions as carbanions – enable the installation via nucleophilic addition of a reactive halomethyl fragment onto a preformed carbon–heteroatom bond. The pronounced thermolability represented – since seminal studies by Köbrich – the Achilles' heel of these reagents: the use of Barbier‐type methodologies (i.e., the electrophile should be present in the reaction mixture prior to the formation of the carbenoid) was pivotal in order to suppress decomposition through α‐elimination processes. Nowadays, the use of low temperatures (?78 °C) guarantees reliable procedures and, significantly, the employment of microreactor technologies allows external trapping to be performed even at higher temperatures as reported by Luisi. We will discuss the α‐halomethyllithium‐mediated homologations of a series of carbon electrophiles such as carbonyl compounds, imines, esters, Weinreb amides, and isocyanates.

     

A New Approach for the Synthesis of Highly Substituted Aromatic Rings: The Alkyne‐Mediated Approach

Pentasubstituted aromatic rings serve as templates for drug design and can be conveniently prepared by the thermolysis of suitably substituted alkynes under microwave conditions.     

Gold‐Catalyzed Cascade Reactions of Furan‐ynes with External Nucleophiles Consisting of a 1,2‐Rearrangement: Straightforward Synthesis of Multi‐Substituted Benzo[b]furans

A gold‐catalyzed cycloisomerization of silyl‐protected 2‐(1‐alkynyl)‐2‐alken‐1‐(2‐furanyl)‐1‐ols with various nucleophiles including water, alcohol, aniline, sulfonamide, and electron‐rich arene has been developed. The method provides a highly efficient access to 5,7‐disubstituted or 2,5,7‐trisubstituted benzo[b]furans with a wide diversity of substituents under mild reaction conditions, which are not easily available by other methods. Remarkably, an interesting rearrangement of the alkyl group from C2 to the C3 position of the furan ring takes place during the cyclization process. The following gold‐assisted allylic substitution enables an elaboration of benzo[b]furans on its side chain of the C5 position with a wide range of functional groups.     

二茂铁亚胺环钯化合物－－一种新型芳基氯化汞偶联催化剂

发现在催化量二茂铁亚胺环钯化合物催化下，芳基氯化汞可在湿和条件下偶联 ，以中等或高的收率生成联芳烃。对于铑盐不能催化偶联的邻位取代苯基氯化汞和 α－基氯化汞，在此体系中亦可发生偶联。以HMPA为溶剂，在x = 0.025（摩尔分 数）化合物1或2催化下与2.0当量氯化锂存在时，得到最好的催化效果。     

Dimerization: First step for micelle preorganization of bile salts

The dimerization constants of sodium cholate, sodium deoxycholate and sodium chenodeoxycholate have been determined in dilute alkaline aqueous solution. The high stabilities of the dimers cannot be explained by single hydrogen bonds but multiple interactions must be involved simultaneously.     

Highly Diastereoselective Synthesis of Methylenecyclobutanes by Merging Boron‐Homologation and Boron‐Allylation Strategies

A highly diastereoselective synthesis of methylenecyclobutanes possessing a quaternary stereocenter is reported, in which boron homologation of an easily‐generated cyclobutenylmetal species is performed, followed by an allylation reaction. Combining three steps in a one‐pot process further optimized the method, which afforded the expected adducts in excellent yields and stereoselectivity, starting from commercially available 4‐bromobutyne.     

Synthesis and Characterization of 6,13‐Diamino‐Substituted Pentacenes

A series of 6,13‐diamino‐substituted pentacenes 1 a – d has been prepared and characterized as a new class of pentacene derivatives with strong donor ability and enhanced solubility in common organic solvents. The spectroelectrochemical and DFT studies revealed that the two‐electron oxidation process was accompanied by the substantial structural change into a butterfly‐like conformation of the pentacene moiety. More importantly, the extent of deformation from the planar pentacene moiety in the dications of 6,13‐diaminopentacene is tunable by varying the N‐substituents.     

Iridium(III) Catalysts with an Amide‐Pendant Cyclopentadienyl Ligand: Double Aromatic Homologation Reactions of Benzamides by Fourfold C−H Activation

The synthesis, characterization, and catalytic performance of iridium(III) catalysts that bear an amide‐pendant cyclopentadienyl ligand ([Cp^AIrI₂]₂) is reported. These [Cp^AIrI₂]₂ catalysts were obtained from the complexation of a Cp^A ligand precursor with [Ir(cod)OAc]₂ followed by oxidation. Double aromatic homologation reactions of benzamides with alkynes by fourfold C?H activation proceeded in good to high yield with these [Cp^AIrI₂]₂ catalysts, demonstrating their superior catalytic performance in this challenging transformation.     

A Sequential Homologation of Alkynes and Aldehydes for Chain Elongation with Optional 13C‐Labeling

Terminal alkynes (RCCH) are homologated by a sequence of ruthenium‐catalyzed anti‐Markovnikov hydration of alkyne to aldehyde (RCH₂CHO), followed by Bestmann–Ohira alkynylation of aldehyde to chain‐elongated alkyne (RCH₂CCH). Inverting the sequence by starting from aldehyde brings about the reciprocal homologation of aldehydes instead. The use of ¹³C‐labeled Bestmann–Ohira reagent (dimethyl ((1‐¹³C)‐1‐diazo‐2‐oxopropyl)phosphonate) for alkynylation provides straightforward access to singly or, through additional homologation, multiply ¹³C‐labeled alkynes. The labeled alkynes serve as synthetic platform for accessing a multitude of specifically ¹³C‐labeled products. Terminal alkynes with one or two ¹³C‐labels in the alkyne unit have been submitted to alkyne–azide click reactions; the copper‐catalyzed version (CuAAC) was found to display a regioselectivity of >50 000:1 for the 1,4‐ over the 1,5‐triazine isomer, as shown analytically by ¹³C NMR spectroscopy.     

毛细管电色谱有机流动相双二元双台阶分离

根据毛细管电色谱中溶质保留值与有机改性剂种类和浓度之间的相互关系，首次实现了毛细管电色谱有机流动相双二元双台阶分离。利用此方法分离含１２种芳香族化合物的混合样品，各组分在六次连续进样中保留时间的ＲＳＤ（％）值均在１．６５％以内，并将样品的分离时间缩短到等度洗脱方式下的三分之一。这说明该方法分离复杂样品快速、可靠。此外还推导了双二元双台阶分离方式下溶质保留值的预测公式，并对该公式的准确性进行了检验，预测值与实测值间的相对误差在５．７３％以内。     

A Novel Pd‐Catalysed Annulation Reaction for the Syntheses of Pyrroloindoles and Pyrroloquinolines

Pd‐catalysed annulation reactions between indole derivatives and internal alkyne esters leading to various pyrrolo[1,2‐a]indoles and pyrroloquinolines have been developed. The strategy involves an intermolecular addition of the indole nitrogen on to the internal alkyne ester followed by an intramolecular insertion of a vinyl–palladium complex into the carbonyl group. This method offers a facile and practical approach to pyrrolo[1,2‐a]indoles and pyrroloquinolines.