Synthesis of 6H-dibenzo[b,d]pyran-6-ones from aryl 3-bromopropenoates via a sequential one-pot procedure using the Sonogashira coupling-benzannulation reaction

Various kinds of 6H-dibenzo[b,d]pyran-6-ones 4 were synthesized via a sequential one-pot procedure using the Sonogashira coupling-benzannulation reaction of aryl 3-bromopropenoates 1, in which the ortho-position of aryl group is substituted with enynes or iodine, with acetylenes 2 in the presence of palladium and copper catalysts. The Sonogashira coupling between the aryl 3-bromopropenoates 1a and 1b, bearing enynes at the ortho-position of aryl group, and alkynes 2a-g gave the enyne intermediates 3 in situ, which subsequently underwent the palladium-catalyzed benzannulation reaction to afford the 6H-dibenzo[b,d]pyran-6-ones 5a-g and 6. The Sonogashira coupling between the aryl 3-bromopropenoate 1c, bearing iodine at the ortho-position of aryl group, and diynes 2f and 2h produced the diyne intermediates 13, which underwent the benzannulation reaction to afford the 6H-dibenzo[b,d]pyran-6-ones 14f and 14h.     

Rhodium‐Catalyzed Cyclization of Diynes with Nitrones: A Formal [2+2+5] Approach to Bridged Eight‐Membered Heterocycles

N‐aryl‐substituted nitrones were employed as five‐atom coupling partners in the rhodium‐catalyzed cyclization with diynes. In this reaction, the nitrone moiety served as a directing group for the catalytic C? H activation of the N‐aryl ring. This formal [2+2+5] approach allows rapid access to bridged eight‐membered heterocycles with broad substrate scope. The results of this study may provide new insight into the chemistry of nitrones and find applications in the synthesis of other heterocycles.     

Synthesis of Unsymmetrical 1,3‐Diynes via Pd/Cu‐Catalyzed Cross‐Coupling of Terminal Alkynes at Room Temperature

A facile and practical synthetic route of unsymmetrical 1,3‐diynes via the PdCl/CuI catalyzed oxidative coupling of two different terminal alkynes has been developed by using 3‐(diphenylphosphino)propanoic acid as a ligand in the presence of oxygen. This system is suitable for not only aromatic alkynes but also heteroaromatic and aliphatic alkynes which were transformed into the corresponding unsymmetrical 1,3‐diynes in moderate to good yields at room temperature. Moreover, the unsymmetrical 1,3‐diynes were also obtained on a multi‐gram scale. Mechanistic studies suggest that oxygen plays a key role in the catalytic cycles.     

Nickel-catalyzed cycloaddition of alkynes and isocyanates

A mild and general route for preparing 2-pyridones from isocyanates and diynes is described. Ni imidazolyidene complexes were used to mediate cyclizations between both internal and terminal diynes with aryl and alkyl isocyanates. In addition, the efficacy of this protocol allows for the preparation of a fused seven-membered pyridone and for three component cyclizations.     

二醇的单保护反应研究进展

综述了近年来二醇的选择性单保护反应的方法, 包括对称二醇的单醚化反应和单酯化反应, 不对称二醇的选择性单醚化反应和单酯化反应, 手性化合物中二醇的选择性单保护反应, 手性试剂和生物催化剂在二醇的选择性单保护反应中的应用. 另外, 还讨论了二醇的选择性单保护反应在天然产物合成中的应用.     

A rhodium(I)-xylyl-BINAP catalyzed asymmetric ynamide-[2+2+2] cycloaddition in the synthesis of optically enriched N,O-biaryls

A rhodium(I)-xylyl-BINAP catalyzed asymmetric [2+2+2] cycloaddition of achiral conjugated aryl ynamides with various diynes is described here. This asymmetric cycloaddition provides a series of structurally interesting chiral N,O-biaryls with excellent enantioselectivity along with a modest diastereoselectivity with respect to both C-C and C-N axial chirality.     

Ruthenium-catalyzed transfer oxygenative cyclization of α,ω-diynes: unprecedented [2 + 2 + 1] route to bicyclic furans via ruthenacyclopentatriene

A novel oxygen-atom-transfer process enables the catalytic [2 + 2 + 1] synthesis of bicyclic furans from α,ω-diynes with DMSO. [CpRu(AN)(3)]PF(6) catalyzed the transfer oxygenative cyclization of diynes with aryl terminal groups, while those of diynes with alkyl terminal groups were effectively promoted by the corresponding Cp* complex. A mechanism for bicyclic furan formation via a ruthenacyclopentatriene was proposed on the basis of both experimental and theoretical studies.     

Zirconocene-mediated, high-yielding macrocyclizations of silyl-terminated diynes

A series of silyl-terminated diynes of varying lengths and substitution patterns have been prepared. These diynes undergo zirconocene coupling with selective formation of trimeric macrocycles from linear alkynes, while nonlinear diynes give cyclodimeric products. The length of the linear diynes can be increased for the preparation of macrocycles with large nanoscale cavities. Reaction of the zirconium-containing macrocycles with acid results in the synthesis of metal-free cyclophanes. All of these macrocycles were prepared in multigram quantities, in the absence of high-dilution conditions, to give products in > 75% yield that are easily purified as crystalline solids.     

A rapid synthesis of 2-alkynylindoles and 2-alkynylbenzofurans

An expeditious synthesis of 2-alkynylindoles and 2-alkynylbenzofuran derivatives has been devised starting from easily available ortho-substituted aryl diynes.     

Palladium-catalyzed dimerization of conjugated diynes: synthesis of (E)-1,2-divinyldiethynylethenes having donor and acceptor chromophores at the terminus of alkyne

(E)-1,2-Divinyldiethynylethenes (DVDEEs) having donor and acceptor chromophores at the terminals of alkyne unit 7' were synthesized by the palladium/HOAc-catalyzed dimerization of the conjugated diynes 8 bearing an Si group at the terminus of alkyne (R(1) position), followed by desilylation and subsequent Sonogashira reaction of the resulting terminal alkyne 10 with aryl iodides.     

Rh-catalyzed cyclization of diynes and enynes initiated by carbonyl-directed activation of aromatic and vinylic C-H bonds

The Rh-catalyzed hydroarylative and hydrovinylative cyclization of diynes with aryl ketones or enones gave monocyclic 1,3-dienes. Enynes also underwent the same reaction and chiral products were obtained with high ee using a chiral Rh catalyst. Carbonyl-directed activation of aromatic and vinylic C-H bonds is likely the initial step in the present transformation.     

1,3-Diyne chemistry: synthesis and derivations

Conjugated diynes have attracted more and more attention not only for their unique rod like structures and wide existence in nature product, but also the abundant properties and derivations of them. Although oxidative dimerization of alkynes or Cadiot–Chodkiewicz reactions were the main pathway and have achieved great success in the synthesis of diynes, oxidative cross coupling, FBW rearrangement as well as diyne metathesis emerged rapidly recently. Moreover, diynes could be precursors of basic heterocycles, which represented an emerging research area. This Letter will cover the recent progresses in the synthesis and further derivations of diynes.     

Polyunsaturated alkyl amides from Echinacea: synthesis of diynes, enynes, and dienes

The synthesis of 20 alkyl amides, including 15 naturally occurring polyunsaturated alkyl amides previously identified from Echinacea spp. (1-13 and 62) or from Achilla sp. (55) and five previously unknown geometric isomers (23, 28, 67, 73, and 80), is described. Importantly, these amides include all of the major alkyl amides present in commercially used Echinacea extracts. The syntheses demonstrate methodology used for constructing alkyl amides containing conjugated diyne and isomerically pure enyne and diene moieties and may be adapted easily for the preparation of other alkyl amides present in Echinacea spp. Terminal-conjugated diynes were prepared by a Cadiot-Chodkiewitz coupling/deprotection sequence utilizing a protected bromoacetylene, and methyl-substituted diynes were made via a base-catalyzed rearrangement of terminal-skipped diynes. Conjugated dienes were prepared conveniently and with high stereoselectivity by the reduction of enynes or diynes with Rieke zinc. With the exception of 1-2 and 11-12, the alkyl amides are synthesized here for the first time, and their NMR data are consistent with that of the reported isolated natural compounds.     

A straightforward method for the synthesis of unsymmetrically substituted 1,3-diynes

An efficient synthetic approach to a variety of unsymmetrically substituted conjugated diynes has been developed, starting from the readily available 1,4-bis(trimethylsilyl)-1,3-butadiyne, based upon the selective and sequential substitution of the trimethylsilyl groups with alkyl, aryl and vinyl groups.     

Ligand‐free Pd/Cu‐catalyzed decarboxylative coupling of aryl iodides with α‐oxocarboxylates

This paper describes a palladium/copper‐catalyzed decarboxylative coupling of aryl iodides with α‐oxocarboxylates. The cross‐coupling reaction gives high chemical yields of aryl ketones and has wide functional group tolerance, making the transformation an attractive alternative to the traditional cross‐coupling approaches for aryl ketones. Copyright © 2014 John Wiley & Sons, Ltd.     

Effective synthesis of aryl ethers and coumaranones employing the palladium-catalyzed enyne-diyne

Alkyl-, alkoxy-, and aryloxy-substituted conjugated enynes 1 in the presence of Pd(PPh(3))(4) catalyst smoothly underwent the regiospecific [4 + 2] cycloaddition reaction with conjugated alkyl- and alkoxy-substituted symmetric diynes 2 to give multisubstituted aryl ethers 3 in good to high yields. Benzannulation of enynes 1d-g with unsymmetric diyne 6, possessing alkyl and alkoxy groups at acetylenic terminii, in most cases produced an aromatic product 8 with an alkoxy group of diyne attached to the ethynyl moiety of the aromatic product. Remarkably, alkoxy-substituted diynes 2c and 6 underwent the benzannulation reaction with 1 at an unusually low temperature of 0 degrees C! One-pot consecutive benzannulation of alkyl-substituted enynes 1d,e and alkoxy-substituted enynes 1f,g with alkoxy-substituted diynes 2c and 6 followed by protonolysis with TsOH afforded coumaranones 9a-c and 10 in reasonable to high overall yields.     

A nickel-catalyzed route to pyridines

A mild and general route for preparing pyridines from nitriles and diynes is described. Ni/imidazolyidene complexes were used to mediate cyclization alkynes and both aryl and alkyl nitriles at ambient temperature. In addition, the efficacy of this protocol allows for the preparation of a fused seven-membered pyridone and for intermolecular cyclizations. When an asymmetrical diyne was employed, cyclization afforded a single pyridine regioisomer.     

Synthesis of symmetrical and unsymmetrical N,N'-diaryl guanidines via copper/N-methylglycine-catalyzed arylation of guanidine nitrate

CuI/N-methylglycine-catalyzed coupling reaction of guanidine nitrate with both aryl iodides and bromides takes place at 70-100 °C, affording symmetrical N,N'-diaryl guanidines with good to excellent yields. Unsymmetrical N,N'-diaryl guanidines can be assembled via monoarylation of guanidine nitrate with aryl iodides bearing a strong electron-withdrawing group and subsequent coupling with another aryl iodide.     

Copper‐Catalyzed Aerobic Oxidative Transformation of Ketone‐Derived N‐Tosyl Hydrazones: An Entry to Alkynes

A novel strategy involving Cu‐catalyzed oxidative transformation of ketone‐derived hydrazone moiety to various synthetic valuable internal alkynes and diynes has been developed. This method features inexpensive metal catalyst, green oxidant, good functional group tolerance, high regioselectivity and readily available starting materials. Oxidative deprotonation reactions were carried out to form internal alkynes and symmetrical diynes. Cross‐coupling reactions of hydrazones with halides and terminal alkynes were performed to afford functionalized alkynes and unsymmetrical conjugated diynes. A mechanism proceeding through a Cu‐carbene intermediate is proposed for the C? C triple bond formation.     

Copper/oxalohydrazide/ketone catalyzed synthesis of primary arylamines via coupling of aryl halides with aqueous ammonia in water

The coupling reaction of aryl halides with aqueous ammonia was catalyzed by copper/oxalohydrazide/ketone system in water to yield primary arylamines without inert atmosphere. This method was fast and facile. The coupling reaction proceeded at 90 °C for 20-80 min, or at room temperature for a prolonged reaction time. A variety of aryl bromides and iodides were found to be applicable to this three-component catalytic system, which afforded good to excellent isolated yields.