An approach for quinolines via palladium-catalyzed Heck coupling followed by cyclization

2-Iodoaniline reacts with α,β-unsaturated carbonyl compounds in DMF at 100 °C in the presence of a catalytic amount of a palladium catalyst along with a base to afford the corresponding quinolones or quinolines in moderate to good yields.     

Solid-phase synthesis of indolines via palladium-catalyzed cyclization

The solid-phase synthesis of indolines from resin-bound 2-bromophenylacetylated amino acids is described. The exhaustive reduction of solid-support bound amides with borane afforded the requisite secondary amines that, following the palladium-catalyzed intramolecular cyclization and cleavage, provided the corresponding disubstituted indolines.     

Enantioselective synthesis of P-stereogenic benzophospholanes via palladium-catalyzed intramolecular cyclization

Enantioselective or diastereoselective intramolecular cyclization of functionalized secondary phosphines or their borane adducts catalyzed by chiral Pd(diphosphine) complexes gave P-stereogenic benzophospholanes in up to 70% ee. These results provide a new method for the synthesis of chiral phospholanes, which are valuable ligands in asymmetric catalysis. [reaction: see text]     

Formation of homoallyl stannanes via palladium-catalyzed stannylative cyclization of enynes

[reaction: see text] Treatment of 1,6-enynes with tri(n-butyl)tin hydride in the presence of a catalytic amount of palladium acetate leads to the formation of exo-methylenecyclopentanes bearing a tri(n-butyl)stannylmethyl moiety.     

Solid-phase synthesis of skeletally diverse benzofused sultams via palladium-catalyzed cyclization

The solid-phase synthesis of sultams from resin-bound amino acids is described. The sulfonylation of the resin-bound primary amines afforded the requisite secondary amines, after which the intramolecular Buchwald-Hartwig-type coupling forms the C-S bond. A final alkylation on the sulfonamides followed by cleavage provided the corresponding seven-membered sultams.     

Synthesis of dibenzofurans via palladium-catalyzed phenol-directed C-H activation/C-O cyclization

A practical, Pd(0)/Pd(II)-catalyzed reaction was developed for phenol-directed C-H activation/C-O cyclization using air as an oxidant. The turnover-limiting step of the process was found to be C-O reductive elimination instead of C-H activation. This reaction can tolerate a variety of functional groups and is complementary to the previous methods for the synthesis of substituted dibenzofurans.     

An unusual palladium-catalyzed carbonylative cyclization of β-bromovinyl aldehydes leading to lactones

β-Bromovinyl aldehydes are carbonylatively cyclized under carbon monoxide pressure in MeCN at 100 °C in the presence of a catalytic amount of a palladium catalyst along with a base to give the corresponding lactones in high yields.     

Synthesis of highly substituted pyrrolidines via palladium-catalyzed cyclization of 5-vinyloxazolidinones and activated alkenes

N-Tosyl-5,5-divinyloxazolidin-2-one undergoes a palladium-catalyzed decarboxylative cyclization across a range of electrophilic alkenes to give the corresponding pyrrolidine derivatives bearing two contiguous quaternary centres. Alkenes bearing two electron-withdrawing groups are required; pyrrolidines were not formed from mono-activated alkenes. Bulky, electron-rich phosphines promote pyrrolidine formation with less highly electrophilic, doubly activated alkenes, and a dramatic improvement is observed in the presence of iodide.     

Synthesis of carbobicyclic compounds via palladium-catalyzed cyclization/hydrosilylation: evidence for reversible silylpalladation

Cyclization/hydrosilylation of substituted 1-vinyl-1-(3-butenyl)cycloalkanes catalyzed by a 1:1 mixture of (phen)Pd(Me)Cl (1) and NaBAr(4) [phen = 1,10-phenanthroline; Ar = 3,5-C(6)H(3)(CF(3))(2)] formed silylated spirocycles in high yield with excellent regio and diastereoselectivity. Cyclization/hydrosilylation of substituted 3-(3-butenyl)cycloalkenes or 2,3-diallyl-5,6-dimethyl-1,4-hydroquinone diacetate (16) formed silylated fused bicyclic complexes in good yield. Reaction of substituted 1,6,11-nonatrienes with silane catalyzed by 1/NaBAr(4) led to cascade cyclization with hydrosilylation. This latter procedure was employed in the synthesis of silylated bicyclopentanes and a linear triquinane.     

An aza cyclopropylcarbinyl-homoallyl radical rearrangement-radical cyclization cascade. Synthesis of dibenzoimidazoazepine and oxazepine derivatives

The cycloaddition of the dibenzoxazepinium W-ylides, generated by heating of trans-1-aryl-7,11b-dihydro-1H-azirino[1,2-a]dibenzo[c,f]azepines, to the C═N double bond of 3-aryl-2H-azirines proceeds endo-stereoselectively giving regioisomeric cycloadducts in ca. 1:1 ratio, in good overall yields. In contrast to the dibenzoxazepinium ylides, the cycloaddition of the dibenzazepinium W-ylide proceeds regioselectively but without exo-endo-stereoselectivity. The reasons for this selectivity of the cycloaddition theoretically were studied at the DFT B3LYP/6-31G(d) level. Heating adducts, (2aRS,13SR,13aRS)-13,13a-diaryl-13,13a-dihydro-1H,2aH-azireno[1',2':3,4]imidazo[1,2-d]dibenzo[b,f][1,4]oxazepines and (2aRS,13SR,13aRS)-13,13a- diphenyl-2a,7,13,13a-tetrahydro-1H-azireno[1',2':3,4]imidazo[1,2-a]dibenzo[c,f]azepine, with an excess of AIBN in toluene gave new polyheterocyclic systems via a novel aza cyclopropylcarbinyl-homoallyl radical rearrangement-radical cyclization cascade. The energy profile of the cascade was studied at the DFT UB3LYP/6-31G(d) level. The transient imidazolinylmethyl radical was trapped by the use of other radical initiators as the corresponding peroxide or alcohol.     

Uncommon intramolecular palladium-catalyzed cyclization of indole derivatives

A novel synthetic strategy based on the intramolecular palladium-catalyzed oxidative cyclization reaction, allows the formation of C-C bond and the synthesis of β-carbolinones. The reaction has been performed in the presence of catalytic amount of PdCl₂(CH₃CN)₂ and benzoquinone as a reoxidant.     

A facile synthesis of indolo[3,2,1-jk]carbazoles via palladium-catalyzed intramolecular cyclization

A new efficient synthesis of indolo[3,2,1-jk]carbazoles by the palladium-catalyzed cyclization of N-(2-bromoaryl)carbazoles is described. The reaction involves intramolecular C-C bond formation, coupled with the cleavage of a C-X bond and a C-H bond on carbazole ring. Substitutions on N-aryl core with either electron-donating or electron-withdrawing groups are introduced, and different reaction factors for cyclization are evaluated.     

An unexpected palladium-catalyzed cyclization of bis-hydroxy allylic alcohols to dioxabicyclo[2.2.2]octanes

The palladium(II)-catalyzed cyclization of bis-hydroxy allylic alcohols afforded quantitatively a mixture of (3-alkyl-5-vinyltetrahydrofuran-3-yl)methanol and 4-alkyl-1-methyl-2,6-dioxabicyclo[2.2.2]octane.     

New Heck coupling strategies for the arylation of secondary and tertiary amides via palladium-catalyzed intramolecular cyclization

A new synthetic protocol has been developed for the arylation of secondary and N-alkylated amide Heck precursors by the implementation of the palladium-catalyzed intramolecular Heck reaction strategies.     

Regioselectivity on the palladium-catalyzed intramolecular cyclization of indole derivatives

Indole 2-carboxamide derivatives 4 underwent palladium-catalyzed intramolecular cyclization reactions to afford beta-carbolinones or pyrazino[1,2-a]indoles according to different reaction pathways. The complete regioselectivity of the reactions was obtained in different reaction conditions.     

Preparation of the 4-hydroxytryptamine scaffold via palladium-catalyzed cyclization: a practical and versatile synthesis of psilocin

[reaction: see text] The 4-hydroxytryptamine scaffold of psilocin was successfully prepared via palladium-catalyzed cyclization of protected N-tert-butoxycarbonyl-2-iodo-3-methoxyaniline and an appropriately substituted silyl acetylene. Removal of the protecting groups afforded psilocin in good yield.     

Synthesis of a TMC-95A ketomethylene analogue by cyclization via intramolecular Suzuki coupling

[structure: see text] A TMC-95A analogue extended at the C-terminus with NlePsi[COCH(2)]Gly-Ala-Ala-NH(2) was synthesized via side-chain cyclization of the linear precursor by a Suzuki cross-coupling reaction in solution to analyze the effect of additional P' residues on the inhibitory potency against yeast proteasome.     

Synthesis of novel tetrahydroindeno[1,2-b]pyrrolidines via Ugi multicomponent and palladium-catalyzed aerobic oxidative cyclization

Novel tetrahydroindeno[1,2-b]pyrrolidines were conveniently prepared in moderate to good yields via a sequential Ugi multicomponent reaction or Staudinger/aza-Wittig/Ugi combination, followed by the palladium-catalyzed aerobic oxidative cyclization of the resulting Ugi adducts.