Deprotection of pinacolyl boronate esters via hydrolysis of intermediate potassium trifluoroborates

An efficient two-step procedure for the deprotection of pinacolyl organoboronate esters is described. Reaction with excess potassium hydrogen fluoride produces the corresponding stable, crystalline potassium organotrifluoroborate salts. Treatment of the trifluoroborates with either inorganic base or trimethylsilyl chloride and water affords the corresponding organoboronic acid in high yield.     

Dioxazaborocanes: old adducts, new tricks

Dioxazaborocanes are boronic adducts obtained by condensation of diethanolamine derivatives with boronic compounds. They were first described in the mid-1950's as a practical way to isolate a boronic adduct. Their use has for a long time been restricted to this purpose for the isolation and characterisation of either a final product or a boronic intermediate. Only recently have they been directly involved in chemical transformations in which they proved equivalent or superior to their acid counterpart. In the meantime they have also been used as protected boronic acids. We wish to show in this report that they will likely represent a fluoride-free alternative to organotrifluoroborate salts and therefore an area of intense development.     

Synthesis of amphidinolide E C10-C26 fragment

The key C10-C26 fragment in a total synthesis of (-)-amphidinolide E has been prepared from an oxolane-containing C10-C17 segment (9, derived from L-glutamic acid) via a Julia-Kocienski reaction with aldehyde 3, followed by a Sharpless AD to obtain the desired diol. The C22-C26 fragment was installed by means of an efficient Suzuki-Molander coupling, with an organotrifluoroborate reagent (4, arising from a cross-metathesis reaction between a vinylboronate and 2-methyl-1,4-pentadiene).     

Exploration of the reaction of potassium organotrifluoroborates with porphyrins

A general method that uses potassium organotrifluoroborates in the Suzuki-Miyaura cross-coupling reaction with ring-brominated porphyrins has been investigated. The reaction conditions tolerate various functional groups and are applicable to the meso- and β-position as well as to aryl- and alkyl-substituted porphyrins. Depending on the nature of the potassium organotrifluoroborate, the coupling products can be obtained in yields of up to 75%.     

Multicomponent and one-pot synthesis of trisubstituted pyridines through a Pd-catalyzed cross-coupling/cross-coupling/cycloaddition sequence

Trisubstituted pyridines are regioselectively synthesized through multicomponent and one-pot processes promoted by a bifunctional Pd-catalyst. The process involves formation of an enamine by Pd-catalyzed amination of an alkenyl bromide, formation of a 2-aza-1,3-butadiene by Pd-catalyzed cross-coupling of a trimethylsilylimine with an alkenyl bromide, and Lewis acid catalyzed cycloaddition between the enamine and the azadiene.     

有机三氟硼酸钾参与的Suzuki偶联反应研究进展

Suzuki偶联反应是构筑碳-碳单键的重要方法之一。 继有机硼酸后,有机三氟硼酸盐成为一种理想的、具有研究意义和使用价值的有机硼亲核试剂。 本文系统地综述了有机三氟硼酸钾参与的Suzuki偶联反应研究进展并对其研究前景进行了展望。     

Synthesis of self-doped polyaniline bearing phosphonic acid moiety via Pd-catalyzed phosphonation of poly(2-bromoaniline)

Self-doped conducting polyaniline bearing phosphonic acid moiety was synthesized via the Pd-catalyzed phosphonation of poly(2-bromoaniline) as a key reaction.     

Highly enantioselective partial hydrogenation of simple pyrroles: a facile access to chiral 1-pyrrolines

A highly enantioselective Pd-catalyzed partial hydrogenation of simple 2,5-disubstituted pyrroles with a Br?nsted acid as an activator has been successfully developed, providing chiral 2,5-disubstituted 1-pyrrolines with up to 92% ee.     

A concise asymmetric synthesis of cis-2,6-disubstituted N-aryl piperazines via Pd-catalyzed carboamination reactions

A concise, modular, asymmetric synthesis of cis-2,6-disubstituted piperazines from readily available amino acid precursors is described. The key step in the synthesis is a Pd-catalyzed carboamination of a N1-aryl-N2-allyl-1,2-diamine with an aryl bromide. The products are obtained in 14-20:1 dr, with >97% ee, and the key cyclizations are the first examples of six-membered ring formation via Pd-catalyzed carboamination reactions of unsaturated amines with aryl halides.     

Solvent control of product diversity in palladium-catalyzed addition of arylboronic acid to aryl aldehydes

In Pd-catalyzed arylboronic acid addition to aryl aldehydes, the expected carbinol or asymmetrical ether can be obtained as the major product by altering aqueous solvent composition. Exploiting this methodology with 2-formylbiphenyls as reaction partner, a fluorene scaffold can be readily constructed in two steps.     

Pd-catalyzed desulfitative Heck coupling with dioxygen as the terminal oxidant

A Pd-catalyzed desulfitative Heck-type reaction of aromatic sulfinic acid sodium salts with various olefins is developed with O(2) as the terminal oxidant under mild conditions. The presence of phosphane ligand DPEphos in anisole can significantly enhance the reaction selectivity.     

Synthesis of gamma,delta-unsaturated and delta,epsilon-unsaturated alpha-amino acids from fragmentation of gamma- and delta-lactones

A noncoded amino acid of cyclomarin A (1) was synthesized in a racemic fashion. The method employs a six-membered ring template to control the relative stereochemistry and introduction of the functional groups. Ultimately, Pd-catalyzed fragmentation of the lactone provided gamma,delta-unsaturated and delta,epsilon-unsaturated alpha-amino acids. A Pd-catalyzed ring opening of a gamma-lactone is also reported.     

The palladium catalyzed asymmetric addition of oxindoles and allenes: an atom-economical versatile method for the construction of chiral indole alkaloids

The Pd-catalyzed asymmetric allylic alkylation (AAA) is one of the most useful and versatile methods for asymmetric synthesis known in organometallic chemistry. Development of this reaction over the past 30 years has typically relied on the use of an allylic electrophile bearing an appropriate leaving group to access the reactive Pd(π-allyl) intermediate that goes on to the desired coupling product after attack by the nucleophile present in the reaction. Our group has been interested in developing alternative approaches to access the reactive Pd(π-allyl) intermediate that does not require the use of an activated electrophile, which ultimately generates a stoichiometric byproduct in the reaction that is derived from the leftover leaving group. Along these lines, we have demonstrated that allenes can be used to generate the reactive Pd(π-allyl) intermediate in the presence of an acid cocatalyst, and this system is compatible with nucleophiles to allow for formation of formal AAA products by Pd-catalyzed additions to allenes. This article describes our work regarding the use of oxindoles as carbon-based nucleophiles in a Pd-catalyzed asymmetric addition of oxindoles to allenes (Pd-catalyzed hydrocarbonation of allenes). By using the chiral standard Trost ligand (L1) and 3-aryloxindoles as nucleophiles, this hydrocarbonation reaction provides products with two vicinal stereocenters, with one being quaternary, in excellent chemo-, regio-, diastereo-, and enantioselectivities in high chemical yields.     

Pd-catalyzed coupling reaction of acid chlorides with terminal alkynes using 1-(2-pyridylethynyl)-2-(2-thienylethynyl)benzene ligand

In the presence of 1-(2-pyridylethynyl)-2-(2-thienylethynyl)benzene as a ligand, the direct synthesis of alkynones has accomplished by a Pd-catalyzed coupling reaction of acid chlorides with terminal acetylenes under mild conditions.     

From Minutes to Years: Predicting Organotrifluoroborate Solvolysis Rates

Organotrifluoroborates solvolyze in water at rates that vary over five orders of magnitude. The negative logarithm of the solvolytic rate constant, pk_(B?F), correlates exceptionally well with the pK_a of the analogous carboxylic acid (R²=0.984). This unforeseen correlation may be of predictive value for several applications including Suzuki–Miyaura cross‐coupling reactions and the design of ¹⁸F‐organotrifluoroborate radioprosthetic groups.     

Tartaric acid-derived chiral phosphite-type P,N-ligands: behavioural features in Pd-catalyzed asymmetric transformations

A practical synthesis of new phosphoramidite, phosphite and diamidophosphite P,N-ligands derived from (R,R)-tartaric acid was carried out. A study of these chiral inducers showed them to provide up to 93% ee in the Pd-catalyzed asymmetric allylations of (E)-1,3-diphenylallyl acetate, up to 84% ee in the Pd-catalyzed asymmetric alkylation of cinnamyl acetate with ethyl 2-oxocyclohexane-1-carboxylate and up to 63% ee in the Pd-catalyzed desymmetrization of N,N′-ditosyl-meso-cyclopent-4-ene-1,3-diol biscarbamate. The effects of the structural modules, such as the nature of the phosphorus-containing ring or exocyclic substituent as well as of the nature of palladium source on the catalytic activity and enantioselectivity were investigated.     

Suzuki–Miyaura Cross‐Coupling of Potassium Organoborates with 6‐Sulfonate Benzimidazoles Using Microwave Irradiation

This article focuses on the utility of organotrifluoroborate salts as coupling partners for Suzuki–Miyaura cross‐coupling with 4‐nitro‐6‐triflyl benzimidazoles using microwave irradiation. The C–C bond formation at the 6‐position of the electron‐rich 1‐,4‐,6‐trisubstituted benzimidazole core is challenging and was not achievable via Kumada, Negishi, Stille, or Heck coupling strategies. Yields of 37–70% could be obtained via palladium coupling strategies utilizing potassium benzyl trifluoroborates as the organometallic coupling partner.     

Dynamic kinetic asymmetric cycloadditions of isocyanates to vinylaziridines

The first examples of the use of racemic vinylaziridines in a Pd-catalyzed dynamic kinetic asymmetric transformation have been examined. Optimization studies of the Pd-catalyzed addition of vinylaziridines to isocyanates revealed that the chiral ligand between trans-1,2-diaminocyclohexane and 2-diphenylphosphino-1-naphthoic acid is superior to that involving 2-diphenylphosphino benzoic acid. Surprisingly, high ee's required the use of an acid whose pKa was about 4.7 +/- 0.1 as a cocatalyst. Both acetic acid and hydroxybenzotriazole meet this requirement. Less electrophilic isocyanates (e.g., benzyl, p-methoxyphenyl) gave higher ee's than more electrophilic ones (phenyl or benzoyl). Both N-benzyl and N-arylaziridines react well to give good yields and ee's, whereas N-tosylaziridines gave lower ee's. A 1,1-disubstituted aziridine led to the formation of a tertiary C-N bond with ee's comparable to the formation of the secondary C-N bond. The products were easily reduced almost quantitatively to the sensitive imidazolidines which can be readily hydrolyzed to the vicinal diamines. The reactivity pattern is consistent with a Curtin-Hammett situation wherein the enantiodiscriminating event is the cyclization of a rapidly equilibrating dynamic pi-allyl palladium intermediate.     

Novel structural derivatives of poly-p-phenylenevinylene

Blends of oligoarylenevinylenes were prepared with polycarbonate, resp. polystyrene. These blends were investigated by electron microscopy as well as by differential scanning calorimetry (DSC) measurements. Block copolymers with well defined arylenevinylene segments were prepared by polycondensation of OH-functionalized oligoarylenevinylenes and aliphatic biscarboxylic acid chlorides. Arylenevinylene functionalized polystyrenes were prepared by Pd-catalyzed coupling reactions.     

Palladium-catalyzed N-arylation of 2-aminothiazoles

A method for the Pd-catalyzed coupling of 2-aminothiazole derivatives with aryl bromides and triflates is described. Significantly, for this class of nucleophiles, the coupling exhibits a broad substrate scope and proceeds with a reasonable catalyst loading. Furthermore, an interesting effect of acetic acid as an additive is uncovered that facilitates catalyst activation.