Tetraorganoindates as nucleophilic coupling partners in Pd-catalyzed cross-coupling reactions

In situ-generated tetraorganoindate complexes from the reaction of 1 equiv of indium trichloride with 4 equiv of appropriate organometallics are efficient nucleophiles in Pd-catalyzed cross-coupling reactions. In this novel reaction tetraorganoindates containing methyl, 1 degree- and 2 degree-alkyl, vinyl, alkynyl, and aryl groups transfer the four organic groups to a variety of electrophiles with high atom efficiency. [reaction: see text]     

Pd-catalyzed direct cross-coupling of electron-deficient polyfluoroarenes with heteroaromatic tosylates

We report a Pd-catalyzed direct cross-coupling of electron-deficient polyfluoroarenes with heteroaromatic tosylates. The notable features of this reaction are its high reaction efficiency, excellent chemoselectivity, operational simplicity, and mild reaction conditions. We have applied this protocol to prepare the semiconducting materials in a highly efficient manner.     

Pd-catalyzed cross-coupling reactions of alkyl halides

Cross-coupling reactions have become indispensable tools for creating carbon-carbon (or heteroatom) bonds in organic synthesis. Like in other important transition metal catalyzed reactions, such as metathesis, addition, and polymerization, unsaturated compounds are usually employed as substrates for cross-coupling reactions. However during the past decade, a great deal of effort has been devoted to the use of alkyl halides as saturated compounds in cross-coupling reactions, which has resulted in significant progress in this undeveloped area by introducing new effective ligands. Many useful catalytic systems are now available for synthetic transformations based on C(sp(3))-C(sp(3)), C(sp(3))-C(sp(2)) and C(sp(3))-C(sp) bond formation as complementary methods to conventional C(sp(2))-C(sp(2)), C(sp(2))-C(sp) and C(sp)-C(sp) coupling. This tutorial review summarizes recent advances in cross-coupling reactions of alkyl halides and pseudohalides catalyzed by a palladium complex.     

Phosphinates as new electrophilic partners for cross-coupling reactions

The use of enol phosphinates as electrophiles for cross-coupling reactions has been explored. Both boronic acids (Suzuki-Miyaura reaction) and stannanes (Stille reaction) couple efficiently with lactam derived phosphinates.     

Phosphorus derivatives of carboranes as ligands for Pd-catalyzed cross-coupling reactions

Carborane-containing phosphine ligands having different steric and electronic properties were synthesized. Testing of these ligands in the Pd-catalyzed Suzuki—Miyaura reaction showed higher catalytic activity for sterically congested phosphine ligands with acceptor carborane substituents.     

Halogenated 2'-chlorobithiazoles via Pd-catalyzed cross-coupling reactions

Halogenated bithiazoles allow facile further functionalization and are, therefore, suitable intermediates for the synthesis of compounds with interesting biological activity or material science properties. The applicability of three coupling methods (Negishi, Suzuki, and Stille) for the synthesis of the title compounds was compared. The Negishi method proved to be troublesome, and side reactions were predominant. The synthesis of the first thiazoleboronic acid ester offered a new method for the formation of bithiazoles, not generally applicable so far. The lower toxicity compared to that of tin organyls make this method an approach with interesting perspectives. The Stille coupling proved to be superior to the other methods and enabled the synthesis of the title compounds with diverse connectivity.     

Controlling site selectivity in Pd-catalyzed oxidative cross-coupling reactions

This paper presents a detailed investigation of the factors controlling site selectivity in the Pd-mediated oxidative coupling of 1,3-disubstituted and 1,2,3-trisubstituted arenes (aryl-H) with cyclometalating substrates (L~C-H). The influence of both the concentration and the steric/electronic properties of the quinone promoter are studied in detail. In addition, the effect of steric/electronic modulation of the carboxylate ligand is discussed. Finally, we demonstrate that substitution of the carboxylate for a carbonate X-type ligand leads to a complete reversal in site selectivity for many arene substrates. The origins of these trends in site selectivity are discussed in the context of the mechanism of Pd-catalyzed oxidative cross-coupling.     

Highly efficient Pd-catalyzed carbonylative cross-coupling reactions with tetraorganoindates

Tetraorganoindates, which were prepared easily from the reaction of 1 equiv of InCl(3) with 4 equiv of organometallics, could be employed as effective nucleophilic cross-coupling partners in Pd-catalyzed carbonylative cross-coupling reactions with a variety of organic electrophiles. The present method gave unsymmetrical ketones and 1,4-diacylbenzenes in good yields with highly efficient transfer of almost all the organic groups attached to the indium under a carbon monoxide atmosphere in THF at 60 degrees C.     

General, robust, and stereocomplementary preparation of beta-ketoester enol tosylates as cross-coupling partners utilizing TsCl-N-methylimidazole agents

We have developed a general, robust, and cost-effective method for the (E)- or (Z)-stereocomplementary enol tosylation of beta-ketoesters using TsCl- N-methylimidazole (NMI)-Et3N or LiOH. TsCl coupled with NMI formed a highly reactive N-sulfonylammonium intermediate. Stereocongested secondary alcohols were smoothly sulfonylated using Ts(Ms)Cl-NMI-Et3N. beta-Ketoesters underwent (E)-selective tosylation using TsCl-NMI-Et3N and (Z)-selective tosylation using TsCl-NMI-LiOH (total of 23 examples; 60%-99% yield). Stereoretentive Negishi and Sonogashira couplings using enol tosylates proceeded successfully to give trisubstituted alpha,beta-unsaturated esters.     

Functionalised butanediacetal-protected 1,2-diols as suitable partners for Pd-catalysed cross-coupling reactions

A new method for the synthesis of dienes and enynes containing chiral 1,2-diols is described. The strategy is based on the Pd-catalysed cross-coupling reactions of a series of vinyl and alkynyl asymmetric butanediacetal-protected building blocks. After the coupling, removal of the protecting group leads to the desired functionalised dienes and enynes.     

Synthesis of unsymmetrical diarylureas via Pd-catalyzed C-N cross-coupling reactions

A facile synthesis of unsymmetrical N,N'-diarylureas is described. The utilization of the Pd-catalyzed arylation of ureas enables the synthesis of an array of diarylureas in good to excellent yields from benzylurea via a one-pot arylation-deprotection protocol, followed by a second arylation.     

Pd-catalyzed efficient one-pot sequential cross-coupling reactions of aryl dihalides

The palladium complex containing N-heterocyclic carbene ligands catalyzes one-pot sequential Heck/Suzuki, Heck/Heck, and Heck/Sonogashira coupling reactions of aryl dihalides to afford unsymmetrically substituted arenes in excellent yields.     

Pd-catalyzed cross-coupling reactions of arenediazonium salts with arylsilanes and aryltrifluoroborates in water

Pd-catalyzed cross-coupling reactions of various arenediazonium salts with ArSi(OR)₃ and KArBF₃ have been achieved in good to excellent yields under simple aerobic conditions in water at room temperature. The functional group tolerance makes these transformations as attractive alternatives to the traditional cross-coupling approaches. Furthermore, the sequence can also be performed in a one-pot domino process, omitting the isolation of the intermediate arenediazonium salt.     

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.     

Pd-catalyzed boronations and cross-coupling reactions of aromatic cobaltadithiolene complexes with aryl halides

The Pd-catalyzed reaction of [CpCo(S2C2(Ph)(Bpin))] (1, Bpin = 4,4,5,5-tetramethyl-1,3,2-dioxaboronate) with 1-iodonaphthalene or 2-bromothiophene gave the cross-coupling product [CpCo(S2C2(Ph)(Ar))] (Ar = 1-Np (4) or 2-Th (5)), although an early paper described the reaction of 1 with 3-bromopyridine or 9-bromoanthracene (Ar = 3-Py (2) or 9-Anth (3)). The boronation of the brominated precursor [CpCo(S2C2(p-C6H4Br)(H))] (7) with Bpin-H in the presence of Pd catalyst gave the expected boronated product [CpCo(S2C2(p-C6H4Bpin)(H))] (8) but also underwent an unexpected direct boronation on the dithiolene carbon to form [CpCo(S2C2(p-C6H4Br)(Bpin))] (9). The brominated complex 7 or [CpCo(S2C2(Ph)(p-C6H4Br))] (10) was synthesized by thermal reaction and the microwave-enhanced reaction relatively gave better yield with shorter reaction time than that of the conventional heating reaction. The cross-coupling reactions of the boronated or [CpCo(S2C2(Ph)(p-C6H4Bpin))] (11) with aryl halides successfully produced the corresponding cross-coupling products such as [CpCo(S2C2(p-C6H4Py)(H))] (12) or [CpCo(S2C2(p-C6H4Anth)(H))] (13) from 8 and [CpCo(S2C2(Ph)(p-C6H4Py))] (14) from 11. The structures of 7, 9, 11, 12, 13 and 14 were determined by X-ray diffraction studies. Electronic absorption maxima (λ_max) due to dithiolene LMCT in dichloromethane solution can be modified in the range of 574-602 nm by a substituent effect on the dithiolene ring. Redox potentials obtained from CV measurement were also reported.     

Highly selective mono-substitution in Pd-catalyzed cross-coupling reactions of 3,6-dichloropyridazine with organozinc compounds

Pd-catalyzed cross-coupling reactions of 3,6-dichloropyridazine (1) with benzyl, aryl, and alkyl organozinc compounds led to selective mono-substitution of one of the chlorine atoms. The subsequent cross-coupling of the resulting monochlorides with RZnCl afforded unsymmetrical 3,6-carbon-disubstituted pyridazines.     

Pd-catalyzed cross-coupling reactions of halogenated 1-phenylpyrazol-3-ols and related triflates

1-Phenyl-1H-pyrazol-3-ol was used as a versatile synthon for the preparation of various 1-phenyl-1H-pyrazole derivatives substituted at C-3 and C-4 of the pyrazole nucleus and at the phenyl ring para-position. Treatment of 1-phenyl-1H-pyrazol-3-ol with triflic anhydride in the presence of base gave 3-trifloyloxy pyrazole, while bromination and iodination yielded the corresponding halogenated derivatives. The obtained scaffolds were used in carbon-carbon bond forming Pd-catalyzed cross-coupling reactions to yield (het)aryl- and carbo-functionally substituted 1-phenyl-1H-pyrazoles.     

Nickel-catalyzed cross-coupling reactions of benzylic zinc reagents with aromatic bromides, chlorides and tosylates

Benzylic zinc reagents prepared by direct insertion of zinc to benzylic chlorides in the presence of LiCl undergo smooth cross-coupling reactions with aromatic chlorides, bromides and tosylates using Ni(acac)(2) and PPh(3) as a catalyst system.