Pd(OAc)2/P(cC6H11)3-catalyzed allylation of aryl halides with homoallyl alcohols via retro-allylation

Allylations of aryl halides take place upon treatment of tertiary homoallyl alcohols with aryl halides in the presence of cesium carbonate and a palladium catalyst. The allylation reaction would consist of the following steps: (1) oxidative addition of aryl halide to palladium, (2) ligand exchange between the halide and the homoallyl alcohol affording aryl(homoallyloxy)palladium, (3) retro-allylation of the palladium alkoxide to generate sigma-allyl(aryl)palladium with concomitant liberation of the relevant ketone, and (4) productive reductive elimination. Since the retro-allylation step proceeds in a concerted fashion via a conformationally regulated six-membered cyclic transition state, the allylation reactions are highly regio- and stereospecific when homoallyl alcohols having a substituted allyl group are used. Whereas triarylphosphine is known to serve as a ligand for the palladium-catalyzed allyl transfer reactions, tricyclohexylphosphine proves to significantly expand the scopes of aryl halides to electron-rich aryl chlorides and of homoallyl alcohols to cyclic homoallyl alcohols. The new arylative ring-opening reactions of cyclic homoallyl alcohols allow for the synthesis of ketones having a branched or linear allylarene moiety at the remote terminus in regio- and stereospecific manners.     

Microwave-assisted palladium-catalyzed allylation of aryl halides with homoallyl alcohols via retro-allylation

The palladium-catalyzed allylation of aryl halides with homoallyl alcohols via retro-allylation proceeds at 200-250 °C in a toluene-DMF mixed solvent using microwave heating. Even at such high temperatures, the regio- and stereospecificity of the allyl transfer reaction is still satisfactory. The amount of the palladium catalyst can be reduced to 0.5 or 0.05 mol %.     

Nickel-catalyzed allylation of allyl carbonates with homoallyl alcohols via retro-allylation providing 1,5-hexadienes

A highly efficient and mild method for the synthesis of 1,5-hexadienes, nickel-catalyzed reactions of Boc-protected allyl alcohols with homoallyl alcohols, has been developed. Nickel-mediated retro-allylation allows for the use of homoallyl alcohols as allylmetal equivalents in the synthesis of 1,5-hexadienes.     

Gallium-mediated allyl transfer from bulky homoallyl alcohol to aldehydes or alkynes: Control of dynamic σ-allylgalliums based on retro-allylation reaction

A new method for the preparation and control of dynamic σ-allylgalliums is disclosed. Upon treatment with a Grignard reagent and gallium trichloride, bulky homoallyl alcohols undergo gallium-mediated retro-allylation reaction to provide σ-allylgallium reagents. The σ-allylgallium reagents generated were applied to carbonyl allylation. The retro-allylation reaction generates (Z)- and (E)-σ-crotylgalliums stereospecifically, starting from erythro- and threo-homoallyl alcohols, respectively. The stereochemically defined crotylgallium reagents effected stereoselective allylation of aldehydes. Allylgallation reaction of alkynes with the allylgallium reagents prepared by retro-allylation is also described.     

Rhodium-catalyzed kinetic resolution of tertiary homoallyl alcohols via stereoselective carbon-carbon bond cleavage

A nonenzymatic kinetic resolution of tertiary homoallyl alcohols has been developed through a rhodium-catalyzed retro-allylation reaction under simple conditions. Selectivity factors of up to 12 have been achieved by employing (R)-H8-binap as the ligand, and the reaction can be conducted on a preparative scale.     

A Light/Ketone/Copper System for Carboxylation of Allylic C−H Bonds of Alkenes with CO2

A photo‐induced carboxylation reaction of allylic C?H bonds of simple alkenes with CO₂ is prompted by means of a ketone and a copper complex. The unique carboxylation reaction proceeds through a sequence of an endergonic photoreaction of ketones with alkenes forming homoallyl alcohol intermediates and a thermal copper‐catalyzed allyl transfer reaction from the homoallyl alcohols to CO₂ through C?C bond cleavage.     

A powerful palladium-catalyzed multicomponent process for the preparation of oxazolines and benzoxazoles

Efficient and convenient three-component couplings of an aryl halide, isocyanide, and an amino alcohol under palladium catalysis provide a range of oxazolines and benzoxazoles in excellent yield.     

Noticeable facilitation of the bismuth-mediated Barbier-type allylation of aromatic carbonyl compounds under solvent-free conditions

When milled together with bismuth shot in the presence of allyl halide, aromatic aldehydes readily underwent a Barbier-type allylation to afford the corresponding homoallyl alcohols in good yield. In contrast to the failure in solution reaction, aromatic ketones also underwent allylic carbonyl addition under solvent-free conditions to give the expected tertiary homoallyl alcohols in moderate to good yield.     

Copper-catalyzed coupling of aryl iodides with aliphatic alcohols

[reaction: see text] A simple and mild method for the coupling of aryl iodides and aliphatic alcohols that does not require the use of alkoxide bases is described. The reactions can be performed in neat alcohol. For more precious alcohols, the etherification was carried out in toluene as solvent using 2 equiv of alcohol. Additionally, the cross-coupling of an optically active benzylic alcohol with an unactivated aryl halide was demonstrated to proceed with complete retention of configuration.     

Synthesis of arylallenes by palladium-catalyzed retro-propargylation of homopropargyl alcohols

Treatment of tertiary homopropargyl alcohol with aryl halide under palladium catalysis provided arylallenes regioselectively. The reaction includes retro-propargylation, which proceeds in a concerted fashion via a cyclic transition state and transfers the stereochemistry of homopropargyl alcohols through C-C bond cleavage. The present method enables the use of homopropargyl alcohols as allenylmetal equivalents.     

Facile construction of the benzofuran and chromene ring systems via PdII-catalyzed oxidative cyclization

[reaction: see text]. We herein report the development of one-pot procedures for the conversion of allyl aryl ethers to 2-methylbenzofurans (via sequential Claisen rearrangement and oxidative cyclization) and for the conversion of aryl homoallyl ethers to chromenes (via direct oxidative cyclization). It is likely that both reactions proceed via a common Pd-catalyzed pathway involving olefin activation, nucleophilic attack, and beta-hydride elimination.     

A novel three-component one-pot pyrimidine synthesis based upon a coupling-isomerization sequence

[reaction: see text] 2,4,6-Tri(hetero)aryl-substituted pyrimidines can be readily synthesized in a three-component one-pot process based upon a coupling-isomerization sequence of an electron-poor (hetero)aryl halide and a terminal propargyl alcohol subsequently followed by a cyclocondensation with amidinium salts.     

Conversion of organic halides to disulfanes using KCN and CS2

A sulfur transfer reagent was produced in situ upon stirring a mixture of KCN and CS₂ in DMF at r.t. for 15 min, which after heating with an alkyl halide or aryl halide and CuI gave the corresponding symmetric dialkyl or diaryl disulfide, respectively, in high to excellent yields.     

One‐Pot Preparation of Unsymmetrical Biaryls via Suzuki Cross‐Coupling Reaction of Aryl Halide using Phase‐Transfer Catalyst in a Biphasic Solvent System

A one‐pot synthetic method of unsymmetrical biaryls was developed via the Suzuki cross‐coupling reaction of aryl halide using a phase‐transfer catalyst in a biphasic solvent system.     

A novel 1,5-benzoheteroazepine synthesis via a one-Pot coupling-isomerization-cyclocondensation sequence

2,4-Di(hetero)aryl substituted 2,3-dihydro 1,5-benzoheteroazepines (hetero = NH, O, S) can be readily sythesized in a one-pot process initiated by a coupling-isomerization sequence of an electron poor (hetero)aryl halide and a terminal propargyl alcohol subsequently followed by a cyclocondensation with 2-amino, 2-hydroxy, or 2-mercapto anilines. In addition, the structures were established unambiguously by an X-ray structure analysis of 7a.     

Phase transfer Pd(O) catalyzed polymerization reactions. I. Synthesis of 1,2-(4,4′;-dialkoxyaryl) acetylene monomers and 1,4-Bis[2-(4′,4″-dialkoxyphenyl)ethynyl]benzene derivatives by phase transfer Pd(O)/Cu(I) catalyzed coupling reactions

Several 1,2-(4,4'-dialkoxyaryl)acetylene monomers containing similar or dissimilar substituents were prepared by one of three variations of a one pot phase transfer Pd(O)/Cu(I) catalyzed coupling of aryl halides with a protected acetylene. The three steps within a single flask involved first coupling of the appropriate 1-halo-4-alkoxybenzene derivative with 2-methyl-3-butyn-2-ol, followed by cleavage of the carbinol group to form an aryl acetylide, and finally a second coupling of an aryl halide with the aryl acetylide. Best results were obtained when elevated temperatures and solid-liquid phase transfer reaction conditions were used. Some 1,4-bis[2-(4',4”-dialkoxyphenyl)ethynyl]benzene compounds were also prepared.     

Indium-mediated one-pot, three-component synthesis of homoallyl alcohol esters without catalysts and dehydrants

Indium-mediated one-pot esterification reaction of acyl chlorides or anhydride by using in situ-prepared homoallyl alcohols from aromatic aldehydes and allyl bromide proceeded smoothly to afford the corresponding homoallyl alcohol esters in high yields within about 1 h, which provided a simple and efficient protocol for the simultaneous allylation and esterification of aldehydes without other catalysts and dehydrants.     

Alkyl‐Group Selection in an Acidic‐Surfactant‐Promoted Reaction of Homoallyl Alcohols and Aldehydes in Water

The hydrophobic effect in the reaction of a homoallyl alcohol with an aldehyde (Yadav's reaction system) under aqueous conditions in the presence of an acidic surfactant was studied indicating the presence of the alkyl‐substituent effect, although not a dramatic one. The DBSA‐promoted reaction proceeds relatively faster when both the homoallyl alcohol and the aldehyde carry a cycloalkyl group (DBSA=4‐dodecylbenzenesulfonic acid). In contrast, the reaction of the substrates having an unbranched alkyl group is relatively more favorable in SDS/HCl than in DBSA (SDS=sodium dodecyl sulfate).     

Total synthesis of hirsutellone B via Ullmann-type direct 13-membered macrocyclization

Total synthesis of Hirsutellone B has been achieved by a convergent synthetic strategy. This synthesis features direct construction of the highly strained 13-membered macrocycle of Hirsutellone B utilizing the Ullmann-type reaction. To the best of our knowledge, this is the first application of macrocyclization utilizing an intramolecular Ullmann-type reaction between an aliphatic alcohol and aryl halide.     

Allyltin tribromide: A versatile reagent involved in the ring-opening of epoxides

This paper presents a versatile reagent for epoxide cleavage. The allyltin tribromide could act as a novel and easily prepared allylation reagent and halide atom donor to convert epoxides to the corresponding homoallyl alcohols and halohydrins in high yields with excellent regioselectivities under mild reaction conditions, respectively. It could also act as a Lewis acid to catalyze the ring opening reactions of epoxides with alcohols.