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Relevant academic research and scientific papers

Hydrogen-bond-directed catalysis: Faster, regioselective and cleaner heck arylation of electron-rich olefins in alcohols

A general method for the regioselective Heck reaction of electronrich olefins is presented. Fast, highly regioselective Pd-catalysed α-arylation of electron-rich olefins, vinyl ethers (1a-d), hydroxyl vinyl ethers (1e,f), enamides (1g,h) and a substituted vinyl ether (1i) has been accomplished with a diverse range of aryl bromides (2a-r), for the first time, in cheap, green and easily available alcohols with no need for any halide scavengers or salt additives. The reaction proceeds with high efficiency, leading exclusively to the a-products, in 2-propanol and particularly in ethylene glycol. In the latter, the arylation can be catalysed at a palladium loading of 0.1 mol% and finish in as short a time as 0.5 h. The remarkable performance of the alcohol solvents in promoting a regiocontrol is attributed to their hydrogen-bond- donating capability, which is believed to facilitate the dissociation of halide anions from PdII, and hence, the generation of a key ionic Pd II-olefin intermediate responsible for the a product. This belief is further strengthened by the study of a benchmark arylation reaction in 21 different solvents. The study revealed that exclusive α-regioselective arylation takes place in almost all of the protic solvents, and there is a rough correlation between the α-arylation rates and the solvent parameter ETN. The method is simpler, cleaner and more general than those established thus far.

PALLADIUM CATALYSED HECK ARYLATION OR VINYLATION OF 1-SUBSTITUTED OLEFINS

The present invention relates to a process for preparing arylated or vinylated olefins.

The Heck reaction of electron-rich olefins with regiocontrol by hydrogen-bond donors

No salt please: Halide scavengers AgOTf and TlOAc are not required for the Heck coupling of electron-rich olefins with aryl bromides and chlorides. Using ammonium additives, these reactions can be carried out in either an imidazolium ionic liquid or a common molecular solvent, thus furnishing 1,1′- disubstituted olefins in high yields with excellent regioselectivities. (Chemical Equation Presented).

Ionic liquid-promoted, highly regioselective Heck arylation of electron-rich olefins by aryl halides

Palladium-catalyzed regioselective Heck arylation of the electron-rich olefins, vinyl ethers 1a-d, enamides 1e-g, and allyltrimethylsilane 1h, has been accomplished in imidazolium ionic liquids with a wide range of aryl bromides and iodides instead of the commonly used, but commercially unavailable and expensive, aryl triflates. The reaction proceeded with high efficiency and remarkable regioselectivity without the need for costly or toxic halide scavengers, leading exclusively to substitution by aryl groups of diverse electronic and steric properties at the olefinic carbon α to the heteroatom of 1a-g and β to the heteroatom of 1h. In contrast, the arylation reaction in molecular solvents led to mixtures of regioisomers under similar conditions. Several lines of evidence point to the unique regiocontrol stemming from the ionic environment provided by the ionic liquid that alters the reaction pathway. The chemistry provides a simple, effective method for preparing branched, arylated olefins and contributes to the extension of Heck reaction to a wider range of substrates.

Significant enhancement of the Stille reaction with a new combination of reagents-copper(I) iodide with cesium fluoride

A systematic investigation for enhancement of Stille reaction using the combination of copper(I) iodide and cesium fluoride was described. Initial route to the target compound involved a double Stille coupling in the carbon-carbon bond formation of the key intermediate 1. Homocoupling has often been observed in this reaction especially when electron-withdrawing substituents are present in conjugation with tin. After extensive optimization, a variety of electronically unfavourable and sterically hindered substrates were coupled in very high yields under mild conditions.

Pd/P(t-Bu)3: A mild and general catalyst for stille reactions of aryl chlorides and aryl bromides

Pd/P(t-Bu)3 serves as an unusually reactive catalyst for Stille reactions of aryl chlorides and bromides, providing solutions to a number of long-standing challenges. An unprecedented array of aryl chlorides can be cross-coupled with a range of organotin reagents, including SnBu4. Very hindered biaryls (e.g., tetra-ortho-substituted) can be synthesized, and aryl chlorides can be coupled in the presence of aryl triflates. The method is user-friendly, since a commercially available complex, Pd(P(t-Bu)3)2, is effective. Pd/P(t-Bu)3 also functions as an active catalyst for Stille reactions of aryl bromides, furnishing the first general method for room-temperature cross-couplings.

Air-stable trialkylphosphonium salts: simple, practical, and versatile replacements for air-sensitive trialkylphosphines. Applications in stoichiometric and catalytic processes.

Trialkylphosphines furnish unusual, sometimes unique, reactivity in a range of transformations. Unfortunately, their utility is compromised by their sensitivity to oxidation. We have examined a simple but powerful strategy for addressing this problem: convert air-sensitive trialkylphosphines into air-stable phosphonium salts via protonation on phosphorus. These robust salts serve as direct replacements for the corresponding phosphines (simple deprotonation under the reaction conditions by a Bronsted base liberates the trialkylphosphine) in a diverse set of applications. [reaction: see text]