Rhodium-catalyzed allyl transfer from homoallyl alcohols to acrylate esters via retro-allylation

Retro-allylation of homoallyl alcohols by rhodium catalysts occurs to generate allylrhodium species. Insertion of acrylate esters to the allylrhodiums proceeds to give the corresponding 2,5-hexadienoate esters in situ. Subsequent isomerization or iterative 1,4-addition takes place in the same pots to furnish the corresponding 2,4-hexadienoate esters or triesters in good yields.     

Palladium-catalyzed stereo- and regiospecific allylation of aryl halides with homoallyl alcohols via retro-allylation: selective generation and use of sigma-allylpalladium

Treatment of tertiary homoallyl alcohol with aryl halide under palladium catalysis resulted in the transfer of the allyl moiety of the homoallyl alcohol to aryl halide and yielded the corresponding cross-coupling product stereo- and regiospecifically. The transfer process includes retro-allylation, which proceeds via a conformationally regulated six-membered transition state. The retro-allylation can be regarded as a method for the stereo- and regiospecific preparation of sigma-allylpalladium.     

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.     

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.     

Direct palladium-catalyzed allylic alkylations of alcohols with enamines: Synthesis of homoallyl ketones

An efficient, direct nucleophilic allylic substitution of α-, β- and γ-substituted alcohols with enamines, using the Pd(OAc)_2/PPh₃ catalyst system and ZnBr₂ as a promoter in CH₂Cl₂ at reflux, is reported. The reaction course was dependent on the steric hindrance at the α- or γ-positions with respect to the functionalized α-carbon, selectively affording in moderate to good yields, α- or γ-homoallyl ketones, the so-called “linear” and “branched” products, respectively.     

Microwave-assisted palladium-catalyzed cross-coupling of aryl and vinyl halides with H-phosphonate diesters

A general and efficient method for the microwave-assisted formation of the C-P bond was developed. Using a prevalent palladium catalyst, Pd(PPh3)4, a quantitative cross-coupling of various H-phosphonate diesters with aryl and vinyl halides was achieved in less than 10 min. The reactions occurred with retention of configuration at the phosphorus center and in the vinyl moiety. Using this protocol, several C-phosphonates, including those bearing nucleoside and cholesteryl moieties, were prepared in high yields.     

Remarkable regioselectivity in microwave-enhanced palladium-catalyzed allylation reaction involving allyltrifluoroborates and aryl halides

An unprecedented cross-coupling reaction of potassium allyltrifluoroborates and aryl halides to the corresponding trans-β-methylstyrenes in the presence of PdCl₂(d^tbpf) catalyst under microwave heating was developed.     

Allylic phosphinates via palladium-catalyzed allylation of H-phosphinic acids with allylic alcohols

A novel catalytic allylation of H-phosphinic acids is described. Using Pd/xantphos (2 mol %), H-phosphinic acids react directly with allylic alcohols to produce P-allylated disubstituted phosphinic acids.     

Highly efficient water promoted allylation and propargylation of arylepoxides via rearrangement-carbonyl addition

A simple and highly efficient one-pot procedure for allylation and propargylation of arylepoxides has been developed. A combination of SnCl₂ and catalytic Pd(0) or Pd(II) promotes the reaction of organic halides and epoxides in DMSO with controlled water addition, leading to the regioselective formation of the corresponding homoallyl and homopropargyl alcohols in good yields.     

TfOH-catalyzed allylation of alkynes with cyclic Baylis-Hillman alcohols

The substitution reaction of cyclic Baylis-Hillman alcohols with arylacetylenes was achieved under the catalysis of TfOH in nitromethane. The γ,δ-unsaturated ketones were obtained in moderate to good yields.     

Pd-nanoparticles catalyzed denitrogenative coupling of aryl halides with arylhydrazines: Greener approach for biaryls synthesis under ligand-free condition

The greener approach for the synthesis of biaryl using palladium nanoparticle (Pd–NPs) catalyzed denitrogenative coupling between aryl hydrazine and aryl halides under ligand-free condition has been described. The phytochemicals of the black pepper extract plays a dual role in reduction of Pd^II to Pd⁰ and acts as stabilizing agent for Pd–NPs. The electronically diver's arylhydrazines and commercially available aryl halides are used for the synthesis of symmetrical and unsymmetrical biaryls in good to excellent yield. The mechanism is well supported by control experiment and the recyclability, turnover number and turnover frequency of biogenically synthesized Pd–NPs is studied.     

Solvent-free palladium-catalyzed CO cross-coupling of (hetero)aryl halides with primary alcohols

A new efficient solvent-free procedure for the CO cross-coupling between (hetero)aryl halides with phenols, primary alkanols, or (hetero)arylmethanols using Pd₂(dba)₃/Bu^tBrettPhos catalytic system is proposed using 23 examples.     

Synthesis of amides via palladium-catalyzed amidation of aryl halides

A new and efficient method for the synthesis of amides via palladium-catalyzed C-C coupling of aryl halides with isocyanides is reported, by which a series of amides were formed from readily available starting materials under mild conditions. This transformation could extend its use to the synthesis of natural products and significant pharmaceuticals.     

A simple catalyst system for the palladium-catalyzed coupling of aryl halides with terminal alkynes

A convenient catalyst system consisting of Pd(OAc)₂, PPh₃, K₃PO₄ and DMSO was found to be effective for the coupling reaction of aryl halides with terminal alkynes as well as the deacetonative coupling reaction using a 4-aryl-2-methylbut-3-yn-2-ol as a terminal alkyne precursor. An iminophosphine as a ligand worked more effectively for some combination of substrates than triphenylphosphine.     

Stereocontrolled palladium-catalysed umpolung allylation of aldehydes with allyl acetates

In the present work the stereocontrolled palladium-catalysed umpolung allylation of aldehydes is described. Allyl acetates are in situ transformed into the corresponding allyl boronates, which directly react with aldehydes. The question of stereocontrol is raised by employing (a) chiral boronating agents (reagent control) and by (b) utilising chiral aldehydes (substrate control). These studies reveal that the approach based on substrate control is superior to the former one with respect to yields and stereoselectivity. Remarkably, this umpolung protocol often yields the 4,5-syn products in high selectivity, which is unprecedented for direct crotylations.     

Development of a palladium-catalyzed decarboxylative cross-coupling of (2-azaaryl)carboxylates with aryl halides

A catalytic method for the decarboxylative coupling of 2-(azaaryl)carboxylates with aryl halides is described. The decarboxylative cross-coupling presented is mediated by a system catalytic in both palladium and copper without requiring stoichiometric amounts of organometallic reagents or organoboronic acids. This method circumvents additional synthetic steps required to prepare 2-azaaryl organometallics and organoborates as nucleophilic coupling partners, which are prone to protodemetallation and protodeborylation and produce potentially toxic byproducts.     

Palladium-catalyzed direct allylation of fluorinated benzothiadiazoles with allyl chlorides

A palladium catalyzed cross-coupling of fluorinated benzothiadiazoles (FBTs) with allyl chlorides is reported. The significant feature of this method is synthetic simplicity, providing a straightforward access to unsymmetrical and symmetrical alkylated FBT derivatives that are of interest in organic electronic and optoelectronic materials.     

Microwave-assisted, Mo(CO)6-mediated, palladium-catalyzed amino-carbonylation of aryl halides using allylamine: from exploration to scale-up

Palladium-catalyzed aminocarbonylations of various (hetero)aryl halides with allylamine using Mo(CO)₆ as a solid, in situ CO source, were explored. Microwave-enhanced conditions proved to be highly useful in promoting the conversions in a mere 10-20 min with various (hetero)aryl iodides, bromides and chlorides. The scale-up of a microwave-enhanced aminocarbonylation to 25 mmol scale was performed successfully.     

Pd(OAc)2/dppf as an efficient and highly active catalyst for the allylation of amines, alcohols and carboxylic acids with 1-phenyl-1-propyne

Pd(OAc)₂/1,1′-bis(diphenylphosphino)ferrocene as an efficient, highly active catalyst for the allylation of amines, alcohols and carboxylic acids with 1-phenyl-1-propyne has been developed. The effect of various reaction parameters, such as ligand, time, solvent, temperature, metal: ligand ratio and catalyst concentration on yields of the product were investigated. The optimized procedure works well under mild operating conditions and permits rapid generation of a library for various allylated products.