AIBN-initiated radical addition of gem-difluorinated alkyl iodides to alkynes and the Pd-catalyzed Sonogashira coupling reaction of E-phenyl difluoromethylene vinylic iodides with terminal alkynes

The addition of gem-difluorinated alkyl iodides to alkynes initiated by AIBN neatly gave the corresponding difluoromethylene vinyl iodides among which the stereoselectivity of aromatic acetylenes was high. The further coupling reaction of E-phenyl difluoromethylene vinyl iodides with terminal alkynes in the presence of catalytic palladium afforded the substituted difluorinated enynes.     

Efficient synthesis of trisubstituted alkenes in an aqueous-organic system using a versatile and recyclable Rh/m-TPPTC catalyst

We have found that the use of [Rh(cod)OH]₂ associated with the water-soluble ligand m-TPPTC was highly efficient for the Rh-catalyzed arylation of alkynes. Aryl and alkyl alkynes were transformed to alkenes using 3 mol % rhodium catalyst and 2.5 equiv of boronic acid at 100 °C in a biphasic water/toluene system in 80-99% yield. The reaction was found to be totally regioselective for alkyl arylalkynes and alkyl silylated alkynes. The Rh/m-TPPTC system was for the first time recycled with no loss of the activity and with excellent purity of the desired alkene.     

N-triflyl-propiolamides: Preparation and transamidation reactions

N-Trifluoromethylsulfonyl-propiolamides have been prepared by two methods: a) N-triflation of secondary acetylenic carboxanilides, prepared in two steps from terminal alkynes, with triflic anhydride (Tf₂O) and b) from terminal alkynes and an aryl or alkyl isocyanate followed by Tf₂O in a consecutive one-pot reaction. The title compounds are bench-stable and insensitive to water and alcohols but amenable to transamidation reactions with a wide range of amine nucleophiles. Conversely, they are excellent reagents for the propynoylation of ammonia, primary and secondary amines, anilines, and hydrazines.     

Palladium-catalyzed carbonylative annulation of terminal alkynes: synthesis of coumarins and 2-quinolones

o-Iodophenols and o-iodoaniline derivatives react with terminal alkynes under 1 atm of CO in the presence of pyridine and catalytic amounts of Pd(OAc)₂ to generate coumarins and 2-quinolones, respectively, as the only products. Terminal alkynes bearing alkyl, aryl, silyl, hydroxyl, ester and cyano substituents are effective in these processes affording the desired products in moderate yields. The formation of coumarins and 2-quinolones in this process is in stark contrast with all previously described palladium-catalyzed reactions of o-iodophenols or o-iodoanilines with terminal alkynes and CO, which have afforded chromones and 4-quinolones. Moreover, under our reaction conditions terminal alkynes insert into the carbonpalladium bond instead of undergoing a Sonogashira-type coupling as confirmed by an isotope labeling experiment.     

Lewis Acid Mediated Vinyl‐Transfer Reaction of Alkynes to N‐Alkylimines by Using the N‐Alkyl Residue as a Sacrificial Hydrogen Donor

A variety of N‐alkyl‐α,α‐dichloroaldimines were vinylated by terminal acetylenes in the presence of Lewis acids such as In(OTf)₃ or BF₃ ? OEt₂ and hexafluoroisopropanol (HFIP) as an additive. The reaction proceeds at ambient temperature and leads to geometrically pure allylic β,β‐dichloroamines. This approach is complementary to previously reported transition‐metal‐catalyzed vinyl‐transfer methods, which are not applicable to aliphatic imines and are restricted to imines that contain an electron‐withdrawing nitrogen substituent. In the present approach, terminal alkynes were used as a source of the vinyl residue, and the N‐alkyl moiety of the imine acts as a sacrificial hydrogen donor. The additional advantage of this methodology is the fact that no external toxic or hazardous reducing agents or molecular hydrogen has to be used. This new methodology nicely combines a C(sp²)? C(sp) bond formation, hydride transfer, and an unusual cleavage of an unactivated C? N bond, thereby giving rise to functionalized primary allylic amines. A detailed experimental study supported by DFT calculations of the mechanism has been done.     

Synthesis of enol and vinyl esters catalyzed by an iridium complex

Enol and vinyl esters were successfully synthesized by the use of an iridium complex as a catalyst. The reaction of carboxylic acids with terminal alkynes in the presence of catalytic amounts of [Ir(cod)Cl]₂ and Na₂CO₃ gave the corresponding 1-alkenyl esters. The addition of carboxylic acids to alkynes principally took place in the Markovnikov fashion. In addition, by the use of an Ir complex combined with NaOAc various vinyl esters were prepared through the transvinylation between carboxylic acids and vinyl acetate.     

Efficient synthesis of enynes by tetraphosphine-palladium-catalysed reaction of vinyl bromides with terminal alkynes

Through the use of [PdCl(C₃H₅)]₂/cis,cis,cis-1,2,3,4-tetrakis(diphenylphosphinomethyl)cyclopentane as catalyst, a range of vinyl bromides undergoes Sonogashira cross-coupling reaction with a variety of alkynes, leading to the corresponding 1,3-enynes in good yields. The reaction tolerates several alkynes such as phenylacetylene, dec-1-yne, 2-methylbut-1-en-3-yne a range of alk-1-ynols, 3,3-diethoxyprop-1-yne and a propargyl amine. Higher reactions rates were observed in the presence of phenylacetylene, dec-1-yne, but-3-yn-1-ol, pent-4-yn-1-ol, 3,3-diethoxyprop-1-yne or 1,1-dipropyl-2-propynylamine than with propargyl alcohol, 3-methoxy-prop-1-yne or 2-methylbut-1-en-3-yne. This catalyst can be used at low loading even for reactions of sterically hindered vinyl bromides such as bromotriphenylethylene or 2-bromo-3-methyl-but-2-ene.     

Efficient synthesis of substituted quinolines through intramolecular addition of aryl anion to carbonyl carbon

Substituted quinolines were synthesized in three steps from the Boc amides of substituted 2-iodoanilines and alkyl vinyl ketones. This method consists of (1) N-Michael addition of the Boc amide of 2-iodoaniline to alkyl vinyl ketone in the presence of Cs₂CO₃ in MeCN; (2) I-Mg exchange of the adduct with 3.5 equiv of i-PrMgCl·LiCl, and (3) acid-catalyzed reaction (excess AcCl in EtOH) of the resulting alcohol. Six examples are given with good yields.     

3-Iodo-4-chalcogen-2H-benzopyran as a convenient precursor for the sonogashira cross-coupling: synthesis of 3-alkynyl-4-chalcogen-2H-benzopyrans

3-Iodo-4-chalcogen-2H-benzopyran derivatives underwent a direct Sonogashira cross-coupling reaction with several terminal alkynes in the presence of a catalytic amount of Pd(PPh₃)₂Cl₂ with CuI as a co-catalyst, using Et₃N as base and solvent. This cross-coupling reaction proceeded cleanly under mild conditions and was performed with propargylic alcohols, propargylic ethers, as well as alkyl and aryl alkynes, furnishing the correspondent 3-alkynyl-4-chalcogen-2H-benzopyrans in good yields.     

Iron‐Catalyzed Diboration and Carboboration of Alkynes

An iron‐catalyzed diboration reaction of alkynes with bis(pinacolato)diboron (B₂pin₂) and external borating agents (MeOB(OR)₂) affords diverse symmetrical or unsymmetrical cis‐1,2‐diborylalkenes. The simple protocol for the diboration reaction can be extended to the iron‐catalyzed carboboration of alkynes with primary and, unprecedentedly, secondary alkyl halides, affording various tetrasubstituted monoborylalkenes in a highly stereoselective manner. DFT calculations indicate that a boryliron intermediate adds across the triple bond of an alkyne to afford an alkenyliron intermediate, which can react with the external trapping agents, borates and alkyl halides. In situ trapping experiments support the intermediacy of the alkenyl iron species using radical probe stubstrates.     

Stereoselective synthesis of vinylic (Z)-vic-bis(arylchalcogenides)

Alkyne-titanium complexes 3, readily prepared in situ by the reaction of alkynes with Ti(O-i-Pr)₄/2 i-PrMgCl, react with electrophilic chalcogen species under mild conditions to provide the corresponding addition products in fair to good yields. The obtained vinylic vic-bis(arylchalcogenides) 4 are useful synthetic intermediates for introducing vinyl functions into organic molecules.     

Palladium-catalyzed cross-coupling of 2-haloselenophene with terminal alkynes in the absence of additive

We present herein our results of the Sonogashira coupling reaction of 2-haloselenophenes with terminal alkynes catalyzed by PdCl₂(PPh₃)₂, under co-catalyst free conditions and establish a new procedure to prepare (2-alkynyl)-selenophenes in good yields. The reaction proceeded cleanly under mild reaction conditions and was performed with propargylic alcohols, protected propargylic alcohols, propargylic amines, as well as alkyl, and aryl alkynes, in the presence of PdCl₂(PPh₃)₂, Et₃N, DMF, and in the absence of any supplementary additives. In addition, by this protocol (2,5-bis-alkynyl)-selenophenes were also obtained, in a one pot procedure, using 2,5-bis-iodoselenofene with an excess of terminal alkynes.     

Copper-catalysed photoinduced decarboxylative alkynylation: a combined experimental and computational study

Redox-active esters (RAEs) as alkyl radical precursors have demonstrated great advantages for C–C bond formation. A decarboxylative cross-coupling method is described to afford substituted alkynes from various carboxylic acids using copper catalysts CuCl and Cu(acac)₂. The photoexcitation of copper acetylides with electron-rich NEt₃ as a ligand provides a general strategy to generate a range of alkyl radicals from RAEs of carboxylic acids, which can be readily coupled with a variety of aromatic alkynes. The scope of this cross-coupling reaction can be further expanded to aliphatic alkynes and alkynyl silanes using a catalytic amount of preformed copper-phenylacetylide. In addition, DFT calculations revealed the favorable reaction pathway and that the bidentate acetylacetonate ligand of the copper intermediate plays an important role in inhibiting the homo-coupling of the alkyne.

Redox-active esters (RAEs) as alkyl radical precursors have demonstrated great advantages for Cu-catalysed C–C bond formation.     

高选择性透过二氧化硫气体分离膜的研究 （Ⅳ）不同烃基乙烯基亚砜接枝聚乙烯醇膜的透过性能

研究了不同烃基乙烯基亚砜接技聚乙烯醇（ＰＶＡ－ＲＶＳＯ，Ｒ＝Ｍｅ，Ｅｔ，ｔ－Ｂｕ，Ｐｈ）膜对纯ＳＯ２、Ｎ２的透过性能以及ＳＯ２／Ｎ２混合气体的分离性能，结果表明上述膜对ＳＯ２具有高的选择性，对不同烃基乙烯基亚砜接枝膜进行了比较。     

Highly enantioselective addition of linear alkyl alkynes to linear aldehydes

It is discovered that the use of biscyclohexylamine (Cy₂NH) as an additive can greatly enhance the enantioselectivity for the reaction of linear alkyl alkynes with linear aldehydes. The combination of (S)-BINOL (20 mol %), Cy₂NH (5 mol %), ZnEt₂ (2 equiv), and Ti(OⁱPr)₄ (0.5 equiv) catalyzes the reaction at room temperature in diethyl ether solution with 81-89% ee and 57-77% yield.     

Probing the steric limits of rhodium catalyzed hydrophosphinylation. P-H addition vs. dimerization/oligomerization/polymerization

The reactivity of secondary phosphine oxides containing bulky organic fragments in hydrophosphinylation reactions has been investigated using several rhodium based catalysts. Upon heating in a focused microwave reactor, HP(O)(2-C₆H₄Me)₂ adds to prototypical terminal alkynes affording a complex mixture containing 1,2 and 1,1-addition products. Addition of a second ortho-substituent (HP(O)Mes₂) completely suppresses the hydrophosphinylation reaction for alkyl and aryl substituted alkynes. Variations in the temperature, catalyst loading, solvent, and microwave power were unable to induce an addition reaction in the case of HP(O)Mes₂. While this secondary phosphine oxide did not participate in the hydrophosphinylation reaction, it promoted the polymerization of phenylacetylene. HP(O)R₂ substrates are not commonly thought of as innocent ligands for rhodium complexes in reactions involving alkynes due to facile hydrophosphinylation. While this is certainly true for diphenylphosphine oxide, the chemistry presented herein suggests that HP(O)Mes₂ and related bulky secondary phosphine oxides have great potential as valuable ligands for rhodium catalyzed transformations involving alkynes due to their lack of reactivity towards the addition reaction.     

Synthesis of vinyl sulfides under base-free conditions using selenium ionic liquid

A very simple procedure is described for the efficient synthesis of vinyl sulfides by hydrothiolation of terminal alkynes using 1-n-butyl-3-methylimidazolium methylselenite, [bmim][SeO₂(OCH₃)]. The reaction proceeds cleanly under mild, base-free conditions and was performed with aromatic and aliphatic thiols.     

[3+2] Cycloaddition of metal-containing azomethine ylides for highly efficient synthesis of mitosene skeleton

Efficient synthesis of tricyclic indole derivatives bearing a substituent at the 3-position of the indole nucleus was achieved by the [3+2] cycloaddition reaction of transition metal-containing azomethine ylides derived from N-(o-alkynylphenyl)imines with vinyl ethers. Third-row transition metal complexes, especially PtCl₂, turned out to be highly efficient for the reaction of internal alkynes and imidate substrates with wide generality. Moreover, as strong support for the reaction mechanism, the intermediate Pt-carbene complex was found to undergo intramolecular C-H bond insertion reaction to give tetracyclic indoline derivatives when benzyl vinyl ether was employed as a dipolarophile. This protocol provided a facile synthesis of highly functionalized tricyclic indole derivatives found as the basic skeleton of the mitosene family, such as mitomycin C.     

Plant coumarins: XI. Cross coupling reactions with 2-(tosyl)oreoselone

The reaction of a linearly fused furocoumarin, oreoselone, with p-toluenesulfonyl chloride gave 2-tosyloreoselone which showed a high reactivity in palladium-catalyzed cross-coupling reactions with formation of a new carbon-carbon bond. 2-Tosyloreoselone reacted with terminal alkynes in the presence of Pd(PPh₃)₂Cl₂ to give the corresponding 2-alkynylfuro[3,2-g]chromen-3-ones. 2-Aryl(hetaryl)alkynyloreoselones were obtained in high yield directly by palladium-catalyzed reaction of oreoselone with tosyl chloride and aryl(hetaryl)acetylenes. The reaction of 2-tosyloreoselone with aryl(hetaryl)boronic acids in the presence of palladium complexes with uni- and bidentate ligands, tetrabutylammonium bromide, and a base afforded 2-aryl(hetaryl)-substituted oreoselones. 2-Vinyloreoselone was synthesized from 2-tosyloreoselone and potassium trifluoro(vinyl)borate.     

Synthesis of Silaphenalenes by Ruthenium‐Catalyzed Annulation between 1‐Naphthylsilanes and Internal Alkynes through CH Bond Cleavage

Ruthenium‐catalyzed annulation of 1‐naphthylsilanes with internal alkynes afforded silaphenalenes through cleavage of the C?H bond at the 8‐position of the naphthalene. [RuH₂(CO){P(p‐FC₆H₄)₃}₃] efficiently catalyzed the reaction. The use of 1‐naphthyldiphenylsilane as a substrate resulted in a better yield of the annulation product compared to the use of silanes with alkyl groups on the silicon atom. Internal alkynes with both aryl and alkyl groups were tolerated in this reaction.