Microwave-assisted, Pd(0)-catalyzed cross-coupling of diazirines with aryl halides

Pd(0)-catalyzed cross-coupling reactions of diazirines with aryl halides under microwave heating conditions afford a series of substituted olefins. A reaction mechanism involving the migratory insertion of the Pd carbene intermediate is proposed.     

Pd(DIPHOS)2-catalyzed cross-coupling reactions of organoborons with free or polymer-bound aryl halides

Bis[1,2-bis(diphenylphosphino)ethane]palladium(0) [Pd(DIPHOS)2] catalyzes cross-coupling reactions of free or polymer-bound aryl halides with organoboron compounds to produce biaryls in overall yields of 60-96%.     

N-vinylpyridinium and -ammonium tetrafluoroborate salts: new electrophilic coupling partners for Pd(0)-catalyzed Suzuki cross-coupling reactions

N-Vinylpyridinium and -trialkylammonium tetrafluoroborate salts represent a new class of electrophilic coupling partner for Pd(0)-catalyzed Suzuki cross-coupling reactions and give very good to excellent yields of products with a wide range of boronic acids. The salts are easily prepared from activated acetylenes and pyridinium or trialkylammonium tetrafluoroborates to form crystalline, air-stable, and nonhygroscopic crystals. [reaction: see text].     

Atom-efficient cross-coupling reactions of triarylbismuths with acyl chlorides under Pd(0) catalysis

The atom-efficient cross-coupling reaction of triarylbismuths with a variety of aliphatic, aromatic, and hetero-aromatic acyl chlorides was demonstrated to afford high yields of cross-coupled ketones under palladium catalysis. The corresponding cross-coupling reaction with diacid chlorides also furnished bis-coupled ketones in good yields.     

Pd(OAc)2-catalyzed fluoride-free cross-coupling reactions of arylsiloxanes with aryl bromides in aqueous medium

Mild conditions have been developed to achieve the Pd(OAc)2-catalyzed fluoride-free cross-coupling between the aryl bromides and arylsiloxanes in good to high yields in aqueous medium. The success of the reactions requires the presence of poly(ethylene glycol) (PEG) and 3 equiv of sodium hydroxide. The product was easily separated with ethyl ether extraction, and the catalytic system can be reused eight times with high efficiency.     

Palladium(0)-catalyzed suzuki-miyaura cross-coupling reactions of potassium aryl- and heteroaryltrifluoroborates with alkenyl bromides

Efficient palladium(0)-catalyzed Suzuki-Miyaura cross-couplings are described. The reactions involving potassium aryl- and heteroaryltrifluoroborates with alkenyl bromides can generally be carried out using < or =2 mol % of palladium catalyst and 3 equiv of base in toluene/H2O. When stereodefined alkenyl bromides are employed, the resulting styrene derivatives are accessed stereospecifically. A variety of functional groups are tolerated in both coupling partners.     

Highly efficient copper(0)-catalyzed Suzuki-Miyaura cross-coupling reactions in reusable PEG-400

Readily available copper powder with K₂CO₃ as the base was extremely effective catalyst for Suzuki-Miyaura coupling reaction performed in PEG-400, which afforded almost quantitative coupling products of aryl iodides. Using iodine as additive, coupling products of aryl bromides or chlorides could be obtained with moderate to good yields.     

Triphenylphosphine as a ligand for room-temperature Ni(0)-catalyzed cross-coupling reactions of aryl chlorides with arylboronic acids

Room-temperature Ni(0)-catalyzed cross-coupling reactions of deactivated aryl chlorides with arylboronic acids with inexpensive triphenylphosphine (PPh3) as a supporting ligand have been accomplished in good to excellent yields. Air-stable Ni(PPh3)2Cl2 has also been established as catalyst precursor, and highly active nickel catalysts were obtained when the reduction of Ni(PPh3)2Cl2 with n-BuLi was carried out in the presence of an aryl chloride.     

Pd(0) or Pd(II)-catalyzed ring-opening reactions of benzylidene- and alkylidenecyclopropyl ketones and aldehydes

Pd(0) catalyzed reactions of methylenecyclopropyl carbonyl compounds afforded a convenient method for the synthesis of conjugate (E,E)-1,3-diene derivatives 2 in good to excellent yields. Moreover, we also found that Pd(II)-catalyzed reactions of methylenecyclopropyl carbonyl compounds with water gave 1,5-diketones in good to high yields via a carbene-palladium intermediate. The plausible reaction mechanisms have also been provided on the basis of control and ¹⁸O-labeling experiments.     

Preferential oxidative addition in palladium(0)-catalyzed suzuki cross-coupling reactions of dihaloarenes with arylboronic acids

The study of Pd(0)-/t-Bu3P system as a powerful catalyst for the cross-coupling of n,m-dihaloarenes with 1 equiv of arylboronic acids is described. Our work demonstrated that the fate of the regenerated Pd(0) catalyst can be controlled when the appropriate ligand is employed. The results described here may lead to the development of new, efficient processes to conjugate polymers with controlled length which are potentially useful in molecular electronics.     

Room-temperature Ni0-catalyzed cross-coupling reactions of aryl arenesulfonates with arylboronic acids

Room-temperature Ni(0)-catalyzed cross-coupling reactions of aryl arenesulfonates with arylboronic acids are described. The Ni(0) catalyst, derived from Ni(COD)2 and PCy3, proved to be a general one for the Suzuki-Miyaura cross-coupling of a variety of aryl arenesulfonates. The mild reaction condition, the readily availability of the catalyst, and excellent coupling yields make aryl arenesulfonates potentially useful substrates in organic synthesis.     

Synthesis of cystothiazole E and formal syntheses of cystothiazoles A and C by Pd0-catalyzed cross-coupling reactions

The synthesis of the naturally occurring bithiazole (+)-cystothiazole E (1e) is described starting from oxazolidinone 2. It proceeded in 10 steps and an overall yield of 37%. The key reaction of the sequence was a Suzuki cross-coupling between bromobithiazole 4 and the (E)-alkenylboronic acid derived from alkyne 18 (94% yield). Prior to the synthesis, more general investigations related to the cross-coupling of bromobithiazole 4 were undertaken. Whereas Heck reactions failed Suzuki and Stille cross-coupling reactions were successfully conducted. By this means, the alkenylboronic acid derived from alkyne 11 and stannane 12 could be transformed into the corresponding alkenylbithiazoles 13 (92%) and 14 (52%). The Stille cross-coupling of compound 4 and stannane 5 allowed access to aldehyde 21 (97% yield) and paved the way for an alternative route to (+)-cystothiazole E (1e). In addition, aldehyde 21 was transformed into aldol product 22 (72%) which has been used in previous syntheses of cystothiazole A (1a) and C (1c). In this respect, the preparation of compound 21 represents a formal total synthesis of these cystothiazoles.     

The effect of vicinyl olefinic halogens on cross-coupling reactions using Pd(0) catalysis

(trans) 1-Chloro-2-iodoethylene (3), (trans) 1-bromo-2-iodoethylene (4), (trans) 1,2-diiodoethylene (5) and (cis and trans) 1,2-dibromoethylene (11) were reacted under Suzuki, Sonogashira and Negishi cross-coupling conditions using Pd catalysis to obtain mono coupled products. Only olefin template 3 provided the desired coupling products reliably under all reaction conditions. Compound 5 did not provide cross coupled products under any of the reaction conditions used. The Negishi reaction was the only one that worked for templates 4 and 11. Studies indicate that oxidative addition of the most reactive carbon-halogen bond to Pd(0) is followed by elimination of the second halide, when the second halide is a bromide or an iodide. This happens to a much lesser degree when the second halogen is a chloride.     

Rh(I)-catalyzed cross-coupling reactions of alkenyl tosylates with potassium aryltrifluoroborates

RhCl(PPh₃)₃/DPPF was successfully employed as an efficient catalyst in the Suzuki-Miyaura cross-coupling reactions of potassium aryltrifluoroborates with alkenyl tosylates, affording the corresponding products in good to excellent yields.     

Pyridine ligands as promoters in Pd(II/0)-catalyzed C-H olefination reactions

Commercially available pyridine ligands can significantly enhance the rate, yield, substrate scope, and site selectivity of arene C-H olefination (Fujiwara-Moritani) reactions. The use of a 1:1 ratio of Pd/pyridine proved critical to maximize reaction rates and yields.     

Synthesis of alpha-acyl-functionalized azacycles by Pd-catalyzed cross-coupling reactions of alpha-alkoxyboronates with lactam-derived vinyl triflates

Alkoxydienyl- and alkoxystyrylboronates were used for Pd-catalyzed cross-coupling reactions with lactam-derived vinyl triflates. The hydrolysis of the coupling products with alkoxystyrylboronates provided the corresponding alpha-acyl-substituted 3,4-dihydro-(2H)-pyridines and 2,3,4,5-tetrahydroazepines in good to high yields. The hydrolysis of the coupling products with alkoxydienylboronates, performed in the presence of Amberlyst 15, resulted in a Nazarov-type cyclization that afforded hexahydro[1]pyrindin-7-ones and 3,4,5,6,7,8-hexahydro-(2H)-cyclopenta[b]azepin-8-ones. This methodology represents a novel and efficient procedure for the preparation of these classes of azacyclic compounds.     

Directed Pd(0)-catalyzed hydrostannations of internal alkynes

Hydrostannations of primary propargylic alcohols with Bu₃SnH catalyzed by Pd(PPh₃)₂ yield (E) allylic alcohols in which the Bu₃Sn group is affixed to the carbon proximal to the CH₂OH substituent, suggestive of an OH directing effect. Hydrostannations of the related propargylic acetates show no such effect.