Synthesis of 2-alkylidenecyclopentanones via palladium-catalyzed carbopalladation/ring expansion of 1-(1-alkynyl)cyclobutanols

The palladium-catalyzed cross-coupling of aryl halides or vinylic halides or triflates and 1-(1-alkynyl)cyclobutanols affords good yields of stereoisomerically pure 2-arylidene- or 2-(2-alkenylidene)cyclopentanones, respectively. The process involves (1) oxidative addition of the organic halide or triflate to Pd(0), (2) regioselective, intermolecular carbopalladation of the carbon-carbon triple bond of the 1-(1-alkynyl)cyclobutanol to produce a vinylic palladium intermediate, (3) regioselective ring expansion to a palladacycle, and (4) reductive elimination of the 2-alkylidenecyclopentanone with simultaneous regeneration of the Pd(0) catalyst. Generally, the best results are obtained by employing 10 mol % of Pd(OAc)(2), 20 mol % of PPh(3), 2 equiv of the aryl or vinylic iodide or vinylic triflate, 2 equiv of diisopropylethylamine, and n-Bu(4)NCl in DMF as the solvent.     

Synthesis of 3,4-disubstituted isoquinolines via palladium-catalyzed cross-coupling of 2-(1-alkynyl)benzaldimines and organic halides

The palladium-catalyzed cross-coupling of readily available N-tert-butyl-2-(1-alkynyl)benzaldimines and aryl, allylic, benzylic, alkynyl halides, as well as a vinylic halide, provides a valuable new route to 3,4-disubstituted isoquinolines with aryl, allylic, benzylic, 1-alkynyl, and vinylic substituents, respectively, in the 4-position. The reaction appears to require an aryl group on the end of the acetylene furthest from the imine functionality. The reaction conditions have been optimized, and reasonably good yields have been obtained.     

Synthesis of indenes via palladium-catalyzed carboannulation of diethyl 2-(2-(1-alkynyl)phenyl)malonate and organic halides

Highly substituted indenes have been prepared in good yields by the palladium-catalyzed carboannulation of diethyl 2-(2-(1-alkynyl)phenyl)malonate with aryl, benzylic, and alkenyl halides. The reaction conditions and the scope of the process were examined, and a possible mechanism is proposed.     

The first palladium-catalyzed desulfitative Sonogashira-type cross-coupling of (hetero)aryl thioethers with terminal alkynes

An unprecedented desulfitative Sonogashira-type cross-coupling protocol is exemplified by the synthesis of substituted 5-chloro-3-alkynylpyrazinones from the corresponding 5-chloro-3-(phenylsulfanyl) pyrazin-2(1H)-ones. The applicability of the method is extended to solid-phase linked pyrazin-2(1H)-ones as well as to some oxazinones, pyrazines, and phenyl thioesters.     

Synthesis of 2-substituted 3-aroylindenes via palladium-catalyzed carbonylative cyclization of diethyl 2-(2-(1-alkynyl)phenyl)malonates with aryl halides

[reaction: see text] The palladium-catalyzed reaction of readily accessible diethyl 2-(2-(1-alkynyl)phenyl)malonates with aryl halides under a balloon pressure of CO produced 2-substitued 3-aroylindenes in good yields. The reaction is believed to proceed via cyclization of the alkyne containing a proximate nucleophilic center promoted by an acylpalladium complex.     

Carbon-nitrogen bond formation involving well-defined aryl-copper(III) complexes

Carbon-heteroatom bond formation from copper(III) is commonly invoked as a key step in catalytic reactions, including the century-old Ullmann reactions. Well-defined examples of such reactions have never been observed. Here, we demonstrate that a well-defined Cu(III)-aryl species reacts with a variety nitrogen nucleophiles to undergo facile carbon-nitrogen bond formation.     

Synthesis of phosphaisoquinolin-1-ones by Pd(II)-catalyzed cyclization of o-(1-alkynyl)phenylphosphonamide monoesters

A Pd(II)-catalyzed intramolecular cyclization of o-(1-alkynyl)phenylphosphonamide monoethyl esters was examined, and a new class of six-membered phosphorus heterocycles (phosphaisoquinolin-1-ones) were formed with high regioselectivity and good yields. The present reaction is the first example of intramolecular addition of P-NH to substituted alkynes, which provides a valuable way to synthesize novel phosphorus heterocycles with potential bioactivities.     

Synthesis of diporphyrins via palladium-catalyzed C-O bond formation: effective access to chiral diporphyrins

Diporphyrins can be efficiently synthesized from bromoporphyrin precursors via palladium-catalyzed C-O bond formation. The synthetic methodology is general and can be applied to various diols, forming a series of homo-diporphyrins containing different types of spacers in high to excellent yields. Chiral diporphyrins can be readily constructed through the use of optically active diols. A similar strategy allows access to hetero-diporphyrins and triporphyrins, including free-base and metalloporphyrin hetero dimers.     

A new stereospecific cross-coupling by the palladium-catalyzed reaction of 1-alkenylboranes with 1-alkenyl or 1-alkynyl halides

The representative (E)-1-alkenyldisiamylboranes and (E)-1-alkenyl-1,3,2-benzodioxaboroles readily obtainable $\text{via}$ hydroboration of 1-alkynes react with 1-alkenyl halides or 1-alkynyl halides in the presence of a catalytic amount of tetrakis(triphenylphosphine)palladium and base to give corresponding conjugated (E)-dienes or (E)-enynes with high regio- and stereospecificity in good yields, respectively.     

Synthesis of 1-alkynyl(diphenyl)onium salts of group 16 elements via heteroatom transfer reaction of 1-alkynyl(phenyl)-lambda 3-iodanes

1-Alkynyl(phenyl)-lambda 3-iodanes undergo selective transfer of the alkynyl groups over the phenyl group onto diphenyl chalcogens. Exposure of 1-alkynyl(phenyl)-lambda 3-iodanes to diphenyl chalcogens (S, Se, and Te) in dichloromethane or 1,2-dichloroethane affords 1-alkynyl(diphenyl)sulfonium, -selenonium, and -telluronium salts in high yields.     

Efficient preparation of monohydrosilanes using palladium-catalyzed Si-C bond formation

The arylation of dihydrosilanes with aryl iodides or heteroaryl iodides in the presence of a palladium catalyst provides the corresponding monohydrosilanes in good to high yield. Moderate to good yields are obtained even in the presence of a variety of reactive functional groups, such as -NH2, -OH, or -CN, without their protection.     

The preparation and properties of cationic dicarbonylcyclopentadienyliron complexes of organic carbonyl compounds: molecular structure of dicarbonylcyclopentadienyliron(3-methylcyclohexenone) hexafluorophosphate

A number of complexes CpFe(CO)₂(L) (L = aldehyde, ketone, ester, amide) have been prepared either by treatment of [CpFe(CO)₂]₂ or CpFe(Co)₂Br with AgPF₆ in the presence of L or by a ligand exchange reaction employing CpFe(CO)₂(isobutylene)BF₄. NMR spectral data suggest that these complexes involve iron—oxygen σ-bonding rather than π-bonding to the carbonyl group. This is confirmed by an X-ray structure determination of the 3-methylcyclohexenone complex. The exchange stability of these complexes parallels their basicity.     

Synthesis of bulky and electron-rich MOP-type ligands and their applications in palladium-catalyzed C-N bond formation

A series of 2-dialkylphosphino-2'-alkoxy-1,1'-binaphthyl ligands (6a-c and 8a-c) have been prepared conveniently by a lithium-initiated ring-opening reaction of dinaphthofuran, followed by selective phosphorylation. These compounds displayed a remarkable air and moisture stability, both in solid form and in solution. Application of these phosphine ligands in palladium-catalyzed C-N bond forming reactions revealed the crucial roles of the steric bulk of the substituents on the phosphorus atom governing the catalytic activity. Specifically, 2-di-tert-butylphosphino-2'-isopropoxy-1,1'-binaphthyl (8b) proved to be the most effective for the aminations of aryl halides with primary amines, while the less bulky 2-dicyclohexyl-2'-methoxy-1,1'-binaphthyl (6a) was more effective for the aminations with secondary amines. The steric and electronic effects of the ligands were analyzed to account for these observations.     

Synthesis and structure of supramolecular complexes between 1-alkynyl(phenyl)(tetrafluoroborato)-λ-iodanes and 18-crown-6

Slow evaporation of a solution of 1-decynyl(phenyl)(tetrafluoroborato)-λ³-iodane and 18-crown-6 in dichloromethane-diethyl ether-hexane gave a supramolecular 1:1 complex, while 3,3-dimethyl-1-butynyl- and phenylethynyl(phenyl)(tetrafluoroborato)-λ³-iodanes afforded 2:1 complexes. Complexation with 18-crown-6 increased the thermal stability of the phenylethynyl-λ³-iodane. Solid state and solution structures of these complexes were examined by single crystal X-ray analyses, ¹H and ¹³C NMR spectra, and cold-spray ionization MS. Binding constants were measured by ¹H NMR titrations.     

Synthesis of 4-halophosphaisocoumarins via halocyclization of 2-(1-alkynyl)phenylphosphonates

A series of 4-halophosphaisocoumarins were prepared with high regioselectivity in good to excellent yields under mild conditions by the reaction of 2-(1-alkynyl)phenylphosphonic acid diesters with I₂ in CHCl₃ or ICl in CH₂Cl₂, or by the reaction of 2-(1-alkynyl)phenylphosphonic acid monoesters with NBS or NCS in DMF. Whether the alkynylphosphonates could cyclize or not was affected by the substituents, reaction solvents and electrophiles. A rationale for this reaction is discussed.     

Synthesis of 3-iodoindoles by electrophilic cyclization of N,N-dialkyl-2-(1-alkynyl)anilines

[reaction: see text] A wide variety of N-alkyl-3-iodoindoles are readily prepared under very mild reaction conditions by the palladium/copper-catalyzed cross-coupling of N,N-dialkyl-o-iodoanilines and terminal alkynes, followed by electrophilic cyclization by I(2)(). Alkyl-, aryl-, and vinylic-substituted alkynes all undergo iodocyclization in excellent yields.     

Synthesis of omega-(hetero)arylalkynylated alpha-amino acid by Sonogashira-type reactions in aqueous media

Mild conditions are described that allow the palladium-catalyzed cross-coupling of C(alpha)-alkynylated glycine with a wide variety of electron-rich and electron-poor aryl and heteroaryl halides in aqueous media.     

Synthesis, structure, and reaction of 1-alkynyl(aryl)-lambda3-bromanes

Reported here for the first time are the synthesis, structure, and reaction of hypervalent 1-alkynyl(aryl)-lambda3-bromanes. BF3-catalyzed ligand exchange on bromine(III) of p-trifluoromethylphenyl(difluoro)-lambda3-bromane with 1-alkynyl(trimethyl)stannanes in dichloromethane at -78 degrees C afforded 1-alkynyl(aryl)-lambda3-bromanes in good yields. Trimethyl(trimethylsilylethynyl)stannane gave silylethynyl-lambda3-bromane selectively. 13C NMR chemical shifts of acetylenic carbon atoms of alkynylbromanes are compared with those of alkynyl-lambda3-iodanes and explained in terms of the spin-orbit-induced heavy atom effects. The structure of tert-butylethynylbromane was established by a single-crystal X-ray analysis of its crown ether complex. The 1-alkynyl(aryl)-lambda3-bromanes serve as highly electron-deficient Michael acceptors and undergo tandem Michael-carbene rearrangements by the reaction with sulfonate anions, yielding 1-alkynyl sulfonates.     

Synthesis of substituted quinolines by electrophilic cyclization of N-(2-alkynyl)anilines

Quinolines substituted in the 3-position by an iodo or phenylseleno group are readily prepared in good to excellent yields by the reaction of propargylic anilines with appropriate electrophiles under mild reaction conditions. [reaction: see text]