DFT characterisation of a Pd → I adduct, and a Pd complex formed after oxidative alkenylation of Pd by [Ph(alkenyl)I], in Pd-mediated synthesis of benzofurans involving Pd, annulation and chain-walking.

The synthesis of benzofurans by the reaction of the palladium(II) complex Pd{1-CH-2-OCH(COEt)-C,C}(bipy) (bipy = 2,2'-bipyridine) with hypervalent iodine(III) reagents [Ph(CHCHR)I] has been examined by Density Functional Theory. Results highlight the role of oxidative alkenylation to form Pd intermediates and the role of initial adduct formation in this process, an annulation process facilitated by Pd, and the role of 'chain-walking' at Pd centres to allow formation of the lowest energy product. Computation (R = Me) allows assignment of an initially formed adduct with a 'Pd → I' interaction at -50 °C, and, after oxidative alkenylation of Pd and reductive elimination from a Pd centre Ar⋯Alkenyl coupling, formation of a second intermediate with a structure consistent with NMR detection (R = -hexyl) at -30 °C is obtained.

Modular strategy for the synthesis of functionalized aryl-fused azabicyclo[2.2.2]octanes via sequential Cu/Pd/Ru catalysis.

Aryl-fused 2-azabicyclo[2.2.2]octanes were prepared by a novel sequence of Cu-catalyzed three-component coupling of diversely substituted N-benzyl o-bromoaryl imines with methacryloyl chloride and vinyltributyl stannane followed by Pd-catalyzed Heck annulation.

Divergent reaction pathways of homologous and isosteric propargyl amides in sequential Ru/Pd-catalyzed annulations for the synthesis of heterocycles.

Cu-catalyzed three-component coupling of imines with benzoyl chloride and terminal arylalkynes followed by enyne ring-closing metathesis (RCM) and Heck cyclization afforded medicinally relevant benzoindolines, cyclopropane-fused indenopyridines, pyrroloquinolines, or 1,7-tetrahydrophenanthrolines via divergent cyclization pathways. Unexpectedly, the Pd-catalyzed cyclization of heterocyclic dienes proceeded via regiodivergent 5-exo or 6-endo pathways depending on the ring size (n = 1, 2) or the presence of isosteric groups (CH vs N). A one-pot protocol for the enyne-RCM/Heck annulation featuring a sequential addition of the Ru and Pd catalysts was developed maximizing the synthetic efficiency.

Palladacycles: Effective Catalysts for a Multicomponent Reaction with Allylpalladium(II)-Intermediates.

Palladium(II) complexes with an bidentate ligand featuring one C-Pd bond and a Pd-N-donor bond (palladacycles) have been shown to afford improved yields of homoallylic amines from a three-component coupling of boronic acids, allenes and imines in comparison to the yields of homoallylic amines achieved with the originally reported catalyst (Pd(OAc)/P(-Bu)), thus extending the scope of the reaction. P NMR monitoring studies indicate that distinct intermediates featuring Pd-P bonds originate in the reactions catalyzed by either Pd(OAc)/P(-Bu) or the pallada(II)cycle/P(-Bu) systems, suggesting that the role of the pallada(II)cycles is more complex than just precatalysts. The importance of an additional phosphine ligand in the reactions catalyzed the pallada(II)cycles was established, and its role in the catalytic cycle has been proposed.

Application of sequential Cu(I)/Pd(0)-catalysis to solution-phase parallel synthesis of combinatorial libraries of dihydroindeno[1,2-c]isoquinolines.

Parallel solution-phase synthesis of combinatorial libraries of dihydroindenoisoquinolines employing a sequential Cu(I)/Pd(0)-catalyzed multicomponent coupling and annulation protocol was realized. The scope and limitations of the protocol with respect to the substitution pattern in the aryl ring of the indene core, as well as the N-substituent have been defined, revealing that the methodology is compatible with a wide-range of aliphatic linear, branched, and ester functionalized N-substituents. Unexpectedly, the formation of regioisomers featuring a 1,2,3-contiguous substitution pattern in the aromatic ring of the indene core was observed.

Sequential Cu(I)/Pd(0)-catalyzed multicomponent coupling and annulation protocol for the synthesis of indenoisoquinolines.

Copper-catalyzed coupling of imines, vinylstannanes, or alkynes and o-bromoaroyl chlorides followed by Pd(0)-catalyzed annulations afforded indenoisoquinolines. Protocols requiring minimal purifications were developed, providing new methods for the construction of combinatorial libraries.

Solution-phase parallel synthesis of hexahydro-1H-isoindolone libraries via tactical combination of Cu-catalyzed three-component coupling and Diels-Alder reactions.

Parallel solution-phase synthesis of combinatorial libraries of hexahydro-1 H-isoindolones exploiting a novel "tactical combination" of Cu-catalyzed three-component coupling and Diels-Alder reactions was accomplished. Three distinct libraries consisting of 24 members (library I), 60 members (library II), and 32 members (library III) were constructed. Variation of three substituents on the isoindolone scaffold in library I was exclusively achieved by the choice of the building blocks.

Copper-catalyzed multicomponent cascade process for the synthesis of hexahydro-1H-isoindolones.

Copper-catalyzed coupling of imines, dienylstannanes, and acryloyl chlorides followed by a Diels-Alder reaction afforded hexahydro-1H-isoindolones. Diversification of the core via Pd-catalyzed cross-coupling defines a new modular approach to isoindolone combinatorial libraries.

Allylpalladium umpolung in the three-component coupling synthesis of homoallylic amines.

[Structure: see text] Homoallylic amines and alpha-amino esters were prepared via a Pd(II)-catalyzed coupling of boronic acids and 1,2-nonadiene with ethyl iminoacetate or aliphatic, aromatic, and heteroaromatic imines. The allylpalladium umpolung was induced by a Pd(OAc)2 catalyst with commercial phosphine ligands.

A new method for the synthesis of 2-hydroxy-3-nitro-1,4-naphthoquinones: application to regiospecific preparation of unsymmetrical nitrobiquinones.

Novel 2-hydroxy-3-nitro-1,4-naphthoquinones were synthesized by an improved method utilizing nitronium tetrafluoroborate in high yields. A subsequent conversion to 2-chloro-3-nitro-1,4-naphthoquinones and a substitution of the chlorine by hydroxyquinone anions yielded 3-nitro-2,2'-binaphthoquinones with a complete regiocontrol.

Regiocontrolled synthesis and HIV inhibitory activity of unsymmetrical binaphthoquinone and trimeric naphthoquinone derivatives of conocurvone.

Unsymmetrical biquinone and trimeric quinone derivatives were synthesized using halotriflate-biselectrophilic naphthoquinones through stepwise regioselective quinone substitution chemistry and evaluated for their ability to inhibit the cytopathogenic effects of HIV-1 using an MTT colorimetric assay. Compounds were also screened for their ability to inhibit the activity of HIV-1 integrase in vitro. Pyranylated trimeric quinones and biquinones exhibited both antiviral activity and integrase inhibitory activity.

Polymer-supported palladacycles: efficient reagents for synthesis of benzopyrans with palladium recovery. Relationship among resin loading, Pd:P ratio, and reactivity of immobilized palladacycles.

[reaction: see text] Oxapalladacycles were immobilized on polystyrene-divinylbenzene supports and treated with 3-aryl-2-propynoates or 1-alkyl-1,2-propadienes to afford 2H-1-benzopyrans in yields superior to those for solution-phase experiments. Isolation of benzopyrans was facilitated, and 71-80% of the palladium was recovered. Effects of resin loading with phosphorus and palladium were studied, and the optimum immobilized palladacycles featuring a medium loading with P (1.

Regiocontrolled, palladium-catalyzed bisfunctionalization of allenyl esters. Multicomponent coupling approaches to highly substituted alpha,beta-unsaturated delta-lactones.

A palladium-catalyzed regioselective bisfunctionalization of allenyl esters with boronic acids (nucleophiles) and aldehydes (electrophiles) was demonstrated. The three-component coupling afforded alpha,beta-unsaturated delta-lactones under mild conditions and with excellent chemo-, regio-, and diastereoselectivity. Aromatic, heteroaromatic and vinylic boronic acids (R1B(OH)2) reacted with ethyl 2,3-butadienoate and benzaldehyde to afford the corresponding 4-R(1),6-Ph-disubstituted alpha,beta-unsaturated delta-lactones in 62-78% yields.

Regio- and diastereoselective insertion of allenes into stable oxapalladacycles with a metal-bonded stereogenic carbon. preparation of contiguously substituted 3,4-dihydro-2H-1-benzopyrans.

Insertion of monosubstituted allenes into stable oxapalladacycle I was studied. The aim of this work was to define steric and electronic parameters of allenes that would allow for a regio- and diastereoselective synthesis of 2,3-disubstituted 3,4-dihydro-2H-1-benzopyrans, which could not be prepared via related catalytic protocols. Allenes with electron-donating alkyl substituents R sterically unencumbered at the C-3 and C-4 carbons reacted with palladacycles I to afford benzopyrans IV in good yields (45-81%), exclusively as cis diastereomers.

Mechanism of stereoinduction in asymmetric synthesis of highly functionalized 1,2-dihydroquinolines and 2H-1-benzopyrans via nonracemic palladacycles with a metal-bonded stereogenic carbon.

To establish the synthetic utility of palladacycles, a stable racemic benzannulated azapalladacycle featuring a palladium-bonded sp(3)-hybridized stereogenic carbon was prepared and converted into a series of racemic 2,3,4-trisubstituted 1,2-dihydroquinolines via a regioselective insertion of activated alkynes (RCCCOOEt). Analogous diastereomerically enriched azapalladacyle (92% de) and oxapalladacycle (64% de) were synthesized from arylpalladium(II) iodo complexes possessing a nonracemic spectator ligand ((1R,2R)-N,N,N',N'-tetramethyl-1,2-diaminocyclohexane) via an intramolecular displacement of the iodide by an ester enolate. Absolute configurations of the metal-bonded stereocenters in the diastereomerically enriched palladacycles were unequivocally assigned, and the efficiency of stereoinduction was systematically studied.

Synthesis of homoallylic alcohols via palladium-catalyzed three-component coupling of an arylboronic acid with allenes and aldehydes.

[reaction: see text] Racemic homoallylic alcohols have been synthesized by palladium-catalyzed three-component coupling of an arylboronic acid, an allene, and an aldehyde.

Chiral nonracemic late-transition-metal organometallics with a metal-bonded stereogenic carbon atom: development of new tools for asymmetric organic synthesis.

Transition-metal-catalyzed cross-coupling reactions and the Heck reaction have evolved into powerful tools for the construction of carbon-carbon bonds. In most cases, the reactive organometallic intermediates feature a carbon-transition-metal sigma bond between a sp(2)-hybridized carbon atom and the transition metal (Csp(2)--TM). New, and potentially more powerful approach to transition-metal-catalyzed asymmetric organic synthesis would arise if catalytic chiral nonracemic organometallic intermediates with a stereogenic sp(3)-hybridized carbon atoms directly bonded to the transition metal (C*sp(3)--TM bond) could be formed from racemic or achiral organic substrates, and subsequently participate in the formation of a new carbon-carbon bond (C*sp(3)-C) with retention of the stereochemical information.

Synthesis of 2H-1-benzopyrans via palladacycles with a metal-bonded stereogenic carbon.

[reaction: see text] Stable oxapalladacycles have been prepared and converted into a series of highly functionalized 2H-1-benzopyrans via regioselective insertion of activated alkynes.