Palladium(II)-catalyzed conjugate addition of arylsiloxanes in water.

Palladium-phosphinous acids catalyze the conjugate addition of arylsiloxanes to a wide range of alpha,beta-unsaturated substrates in water. A microwave-assisted procedure is described that uses 5 mol % of POPd1 to afford beta-substituted ketones, aldehydes, esters, nitriles, and nitroalkanes in 83% to 96% yield within 4 h. This method eliminates the need for stoichiometric additives and an excess of arylsiloxane, and does not require an inert atmosphere.

Palladium-phosphinous acid-catalyzed NaOH-promoted cross-coupling reactions of arylsiloxanes with aryl chlorides and bromides in water.

A palladium-phosphinous acid-catalyzed and NaOH-promoted coupling method using arylsiloxanes and aryl halides in water has been developed. The POPd1-catalyzed reaction between aryl chlorides or bromides and arylsiloxanes is compatible with various functional groups and affords biaryls in up to 99% yield. This cross-coupling reaction does not require additives such as surfactants or organic cosolvents and proceeds under air, which greatly facilitates operation and catalyst handling.

Chemoselective nucleophilic arylation and single-step oxidative esterification of aldehydes using siloxanes and a palladium-phosphinous acid as a reaction switch.

Aldehydes and siloxanes form methyl esters in a single step through mild oxidative esterification in the presence of a palladium catalyst or, alternatively, afford secondary alcohols via TBAF-promoted arylation in the absence of a catalyst at increased temperatures under otherwise identical reaction conditions.

Palladium-catalyzed chemoselective cross-coupling of acyl chlorides and organostannanes.

Chemoselective cross-coupling of aliphatic and aromatic acyl chlorides with aryl-, heteroaryl-, and alkynylstannanes proceeds in up to 98% yield using 2.5 mol % of bis(di-tert-butylchlorophosphine)palladium(II) dichloride as the precatalyst. Various functional groups including aryl chlorides and bromides that usually undergo oxidative addition to palladium complexes bearing phosphinous acid or dialkylchlorophosphine ligands are tolerated. This procedure allows convenient ketone formation and eliminates inherent limitations of Friedel-Crafts acylations such as substituent-directing effects and typical reactivity requirements of Lewis acid-catalyzed electrophilic aromatic substitutions.

Palladium--phosphinous acid-catalyzed Sonogashira cross-coupling reactions in water.

A palladium--phosphinous acid-catalyzed Sonogashira cross-coupling reaction that proceeds in water under air atmosphere in the absence of organic co-solvents has been developed. Disubstituted alkynes have been prepared in up to 91% yield by POPd-catalyzed coupling of various aryl halides including chlorides in the presence of tetrabutylammonium bromide and pyrrolidine or NaOH.

Use of highly active palladium-phosphinous acid catalysts in Stille, Heck, amination, and thiation reactions of chloroquinolines.

An efficient synthetic route toward a variety of 2,4-disubstituted quinolines has been developed. Alkylation and arylation of 4-chloroquinoline using organolithium reagents proceed with high regioselectivity in position 2 under cryogenic conditions. The intermediate 1,2-dihydro-4-chloroquinoline derivatives are unstable to air and are easily oxidized to the corresponding 2-substituted 4-chloroquinolines in high yields. Highly active palladium-phosphinous acid catalysts POPd, POPd1, and POPd2 have been employed in Stille cross-couplings of quinaldine with arylstannanes and in Heck additions of various 2-substituted 4-chloroquinolines to tert-butyl acrylate. In particular, POPd combines high catalytic activity for cross-coupling reactions with simplicity of use due to its stability to air. Utilizing CsF in POPd-catalyzed Stille couplings further increased the reactivity of arylstannanes, which was attributed to the fluorophilicity of organotin compounds. Basic additives were found to exhibit a significant effect on the yields of the POPd-promoted Heck reactions. In general, dicyclohexylmethylamine affords superior results than NaOAc, Cs(2)CO(3), or t-BuOK. POPd was also found to tolerate amine and thiol substrates and proved to promote carbon-heteroatom bond formation of chloroquinoline derivatives with aliphatic and aromatic amines and thiols, respectively.

Efficient Stille cross-coupling reaction using aryl chlorides or bromides in water.

An efficient Stille cross-coupling reaction using a variety of aryl halides in neat water has been developed. Employing palladium-phosphinous acid catalyst [(t-Bu)(2)P(OH)](2)PdCl(2) allows formation of biaryls from aryl chlorides and bromides in good to high yields. Functional groups such as ketones and nitriles are tolerated, and organic cosolvents are not required. The air stability and solubility in water of the palladium complexes used in this study facilitate operation of the coupling reaction and product isolation. The feasibility of catalyst recycling has also been demonstrated.