Atom-efficient Pd-catalyzed cross-couplings of chloroarenes with triarylbismuth reagents

Various Pd-catalyzed protocols have been developed for the atom-efficient cross-coupling of chloroarenes with triarylbismuth reagents. Using the developed protocols, an efficient synthesis of unsymmetrical biaryls in good to excellent yields was achieved by employing electron-deficient chloroarenes and a range of triarylbismuth reagents.     

Pd-catalyzed atom-economic couplings of triarylbismuth reagents with 2-bromo- and 2,6-dibromochromones and synthesis of medicinally important fisetin

Pd-catalyzed mono- and bis-arylation of chromones was demonstrated using triarylbismuths as threefold aryl transfer atom-economic reagents. This unprecedented study involving functionalized chromones afforded regio-selective mono-arylations leading to functionalized 2-arylchromones in good to high yields. Bis-arylation of 2,6-dibromochromones in one-pot operation furnished 2,6-diarylchromones in moderate to good yields. The present methodology was applied in the synthesis of naturally occurring and medicinally important fisetin molecule in high yield.     

Palladium-catalyzed synthesis of functionalized tetraarylphosphonium salts

An efficient method to synthesize functionalized tetraarylphosphonium salts is described. This palladium-catalyzed coupling reaction between aryl iodides, bromides, or triflates and triphenylphosphine generates phosphonium salts in high yields. The coupling is compatible with a variety of functional groups such as alcohols, ketones, aldehydes, phenols, and amides.     

Palladium-catalyzed cross-couplings of allylic phosphates

A range of palladium-catalyzed cross-coupling reactions can be performed using allylic phosphates as electrophiles. Both conventional heating and microwave irradiation can be used.     

Room-temperature Stille cross-couplings of alkenyltin reagents and functionalized alkyl bromides that possess beta hydrogens

This communication describes a significant expansion in the scope of Stille reactions of Csp3-X electrophiles, specifically, that Pd/P(t-Bu)2Me catalyzes the room-temperature cross-coupling of a variety of functionalized, beta-hydrogen-containing alkyl bromides with an array of alkenyltin reagents. The structure of the phosphine (P(t-Bu)2Me) is well suited for facilitating oxidative addition and avoiding beta-hydride elimination, while the fluoride serves to activate the tin reagent for efficient transmetalation.     

Stille cross-couplings of unactivated secondary alkyl halides using monoorganotin reagents

The first catalyst that achieves Stille cross-couplings of secondary (as well as primary) alkyl halides has been developed. The method employs easily handled and inexpensive catalyst components (NiCl2 and 2,2'-bipyridine) and, through the use of monoorganotin reagents, avoids the formation of toxic and difficult-to-remove triorganotin side products.     

An atom-economic synthesis of functionalized pyrroles via a sequential metal-catalyzed three-component reaction

A three-component reaction of one molecule of imine and two molecules of alkynoates is realized with the catalysis of Cu(I)–Fe(III) in a sequential manner to allow the direct synthesis of functionalized pyrroles, during which, one C–N bond and two C–C bonds are formed with high atom economy. This method benefits from easily available starting materials, low-cost catalysts, and convenient operations.     

Palladium-catalyzed Hiyama cross-couplings of aryl arenesulfonates with arylsilanes

Palladium-catalyzed efficient Hiyama cross-coupling reaction of aryl arenesulfonate with arylsilane is described. The desired carbon-carbon bond formation proceeds under mild conditions with good functional group tolerance.     

Palladium-catalyzed Stille cross-couplings of sulfonyl chlorides and organostannanes

Arene and phenylmethanesulfonyl chlorides can be cross-coupled with aryl, heteroaryl, and alkenylstannanes with desulfitation in the presence of 10 mol % CuBr.Me2S, 1.5 mol % Pd2dba3, and 5 mol % tri-2-furylphosphine in tetrahydrofuran or toluene under reflux. This extension of the Stille cross-coupling reaction realizes a new and economical method for the generation of C-C bonds. The palladium-catalyzed carbonylative Stille cross-coupling reactions of arenesulfonyl chlorides and organostannanes in the presence of CO (60 bar) at 110 degrees C in toluene generate the corresponding ketones. Arenesulfonyl chlorides are more reactive than aryl chlorides and aryl bromides in their Stille cross-coupling with organostannanes but less reactive than aryl iodides. The new methods disclosed for the generation of C-C bonds open new possibilities for medicinal chemistry and material sciences.     

Remote stereocontrol using functionalized allylmetal reagents

Alk-2-enyl(trialkyl)stannanes with heteroatom substituents at the 4-, 5-, and 6-positions are transmetallated stereoselectively using tin(IV) halides to generate allyltin trihalides, which react with aldehydes to give (3Z)-homoallylic alcohols with efficient 1,5-, 1,6-, and 1,7-stereocontrol. This chemistry has been used to develop new strategies for natural product synthesis. Because of the toxicity of organotin reagents and the problems in removing organotin residues from reaction products, alternative procedures that avoid the use of organotin reagents have been investigated. To date, alk-2-enylgermanium reagents have been shown to deliver effective 1,5- and 1,6-stereocontrol, which is analogous to that observed for the organotin compounds. Organobismuth intermediates, which can be generated from allyl bromides and zinc-bismuth(III)iodide, react with aldehydes with efficient 1,5-stereocontrol which is complementary to that observed with the organo-stannanes or -germanes in that (3E)-homoallylic alcohols are obtained.     

Palladium-catalyzed aryl-aryl cross-coupling reaction using ortho-substituted arylindium reagents

A range of biaryl compounds (aryl-aryl, aryl-heteroaryl, and heteroaryl-heteroaryl) can be efficiently prepared by a palladium-catalyzed cross-coupling reaction between ortho-substituted triarylindium reagents and aryl halides. The triarylindium reagents are prepared by directed ortho-lithiation and transmetallation to indium from the corresponding benzene derivatives using various directed metallation groups (DMGs). The reaction proceeds smoothly in high yields and short reaction times with high atom economy (the three aryl groups attached to indium are efficiently transferred).     

Palladium-catalyzed carboboration of alkynes using chloroborane and organozirconium reagents

Three-component coupling of bis(dialkylamino)chloroborane, alkynes and organozirconium reagents proceeded in the presence of palladium catalysts, leading to the formation of stereo-defined alkenylborane derivatives via cis-carboboration of carbon-carbon triple bonds.     

Highly functionalized organolithium reagents for enantiomerically pure alpha-amino acid synthesis

[reaction: see text] Highly functionalized l-serine-derived organolithium reagents have been generated and reacted with a variety of electrophiles, delivering novel enantiomerically pure adducts. These adducts were then converted into homochiral amino alcohols and novel nonproteinogenic alpha-amino acids, including an aspartic acid mimic that has been synthesized in an enantiomerically pure form for the first time.     

Palladium-catalyzed ring opening of azabicyclic olefins with organoindium reagents: a simple, clean, and efficient synthesis of functionalized cyclopentenes

Azabicyclic olefins undergo facile palladium-catalyzed ring opening with organoindium reagents affording trans-3,4-disubstituted hydrazinocyclopentenes in good to excellent yields.     

Palladium catalyzed atom-economic synthesis of functionalized 9-(diarylmethylene)-9H-fluorenes using triarylbismuths in one-pot bis-coupling process

An efficient palladium catalyzed atom-economic synthesis of functionalized 9-(diarylmethylene)-9H-fluorenes has been accomplished in one-pot bis-coupling process using triarylbismuths as organometallic reagents. These bis-couplings in 1 hour short reaction time afforded various 9-(diarylmethylene)-9H-fluorenes in good to high yields.     

Palladium-catalyzed Suzuki-Miyaura cross-couplings of aryl tosylates with potassium aryltrifluoroborates

Pd-catalyzed Suzuki-Miyaura cross-coupling reaction of aryl tosylates with potassium aryl trifluoroborate in the presence of bulky and electron-rich phosphine ligand is described. In addition, a useful chemoselective coupling of an aryl chloride in the presence of a tosyloxy group was demonstrated.     

Palladium-catalyzed Suzuki-Miyaura cross-couplings of sulfonyl chlorides and boronic acids

[reaction: see text] R = tolyl, phenyl, 4-halophenyl, 1-naphthyl, 2-nitrophenyl, benzyl, methallyl, r1 = aryl, heteroaryl, alkenyl. Arene-, arylmethane, and alk-2-ene-1-sulfonyl chlorides undergo Suzuki-Miyaura cross-coupling with arene-, heteroarene-, and alkeneboronic acids in THF at reflux. The reactivity order is ArI > ArSO(2)Cl > ArBr > ArCl.     

A synthesis of 2-vinylcylobutanones using 1-methoxycyclopropyllithium reagents

A facile synthesis of 2-vinylcyclobutanones consists of reductive lithiation of 1-phenylthio-1-methoxycyclopropanes) addition of enals or enones to the resulting α-lithioethers, and acid catalyzed rearrangement of the allylic alcohols thus produced.