More than Bystanders: The Effect of Olefins on Transition-Metal-Catalyzed Cross-Coupling Reactions

α,β-Divinyl tetrahydropyrroles as chiral chain diene ligands in rhodium(I)-catalyzed enantioselective conjugated additions

A series of α,β-divinyl tetrahydropyrroles, synthesized by asymmetric allylic C-H bond activation/conjugated diene addition reaction of ene-2-dienes, were found to be very efficient chiral chain diene ligands in the rhodium-catalyzed conjugated addition of organoboronic acids to various α,β-unsaturated compounds, achieving the desired chiral adducts with good to excellent yields and ee values.

Stereospecific nickel-catalyzed cross-coupling reactions of alkyl ethers: enantioselective synthesis of diarylethanes

Secondary benzylic ethers undergo stereospecific substitution reactions with Grignard reagents in the presence of nickel catalysts. Reactions proceed with inversion of configuration and high stereochemical fidelity. This reaction allows for facile enantioselective synthesis of biologically active diarylethanes from readily available optically enriched carbinols.

Stereospecific cross-coupling of secondary alkyl β-trifluoroboratoamides

The stereospecific cross-coupling of enantioenriched nonbenzylic secondary alkyl boron compounds has been achieved. The high selectivity toward product formation over an undesired β-H elimination pathway is achieved via an intramolecular coordination of an ancillary carbonyl to the metal center in the diorganopalladium intermediate.

Catalytic enantioselective formation of chiral-bridged dienes which are themselves ligands for enantioselective catalysis

This paper reports a method for highly enantioselective Diels-Alder reaction with an acetylene equivalent to produce chiral-bridged dienes. These dienes, by coordination to Rh(I), can serve as catalysts for the enantioselective addition of vinyl or aryl groups to alpha,beta-unsaturated ketones.

Origins of regioselectivity and alkene-directing effects in nickel-catalyzed reductive couplings of alkynes and aldehydes

The origins of reactivity and regioselectivity in nickel-catalyzed reductive coupling reactions of alkynes and aldehydes were investigated with density functional calculations. The regioselectivities of reactions of simple alkynes are controlled by steric effects, while conjugated enynes and diynes are predicted to have increased reactivity and very high regioselectivities, placing alkenyl or alkynyl groups distal to the forming C-C bond. The reactions of enynes and diynes involve 1,4-attack of the Ni-carbonyl complex on the conjugated enyne or diyne. The consequences of these conclusions on reaction design are discussed.

Electronic and steric tuning of chiral diene ligands for rhodium-catalyzed asymmetric arylation of imines

Rhodium-catalyzed asymmetric arylation of imines using electronically and sterically-modified chiral diene ligands gave the corresponding diarylmethylamines in high yield and with high enantioselectivity using just 0.3 mol% of catalyst.

Cross-coupling of aromatic bromides with allylic silanolate salts

The sodium salts of allyldimethylsilanol and 2-butenyldimethylsilanol undergo palladium-catalyzed cross-coupling with a wide variety of aryl bromides to afford allylated and crotylated arenes. The coupling of both silanolates required extensive optimization to deliver the expected products in high yields. The reaction of the allyldimethylsilanolate takes place at 85 degrees C in 1,2-dimethoxyethane with allylpalladium chloride dimer (2.5 mol %) to afford 73-95% yields of the allylation products. Both electron-rich and sterically hindered bromides reacted smoothly, whereas electron-poor bromides cross-coupled in poor yield because of a secondary isomerization to the 1-propenyl isomer (and subsequent polymerization). The 2-butenyldimethylsilanolate (E/Z, 80:20) required additional optimization to maximize the formation of the branched (gamma-substitution) product. A remarkable influence of added alkenes (dibenzylideneacetone and norbornadiene) led to good selectivities for electron-rich and electron-poor bromides in 40-83% yields. However, bromides containing coordinating groups (particularly in the ortho position) gave lower, and in one case even reversed, selectivity. Configurationally homogeneous (E)-silanolates gave slightly higher gamma-selectivity than the pure (Z)-silanolates. A unified mechanistic picture involving initial gamma-transmetalation followed by direct reductive elimination or sigma-pi isomerization can rationalize all of the observed trends.