Palladacycle as highly efficient catalyst for ring opening of oxabicyclic alkenes with organozinc halides

Ring opening reaction of oxabicylic alkenes 4 with in situ prepared organozinc halides 5 was catalyzed by palladacycle 3 with high efficiency. Good yields of the corresponding 1,2-dihydronaphth-1-ols (6) were provided when as low as 0.05 mol% of palladacycle 3 was used. ³¹P NMR study showed that the skeleton of 3 remained intact in the reaction, which implied that palladacycle 3 did not serve as a catalyst precursor but a catalyst in the reaction.     

Rhodium-catalyzed asymmetric ring opening of oxabicyclic alkenes with phenols

The scope of the rhodium-catalyzed asymmetric ring opening reaction of oxabenzonorbornadiene has been extended to include phenolic nucleophiles. The enanatioenriched, functionalized dihydronaphthalene products are highly valuable intermediates for which no other practical methods of preparation are available. A new catalyst system has been developed which allows the use of less reactive o-halophenols. The utility of these products has been demonstrated through their application in the synthesis of benzofuran polycyclic materials.     

Rhodium-catalyzed asymmetric ring opening of oxabicyclic alkenes with sulfur nucleophiles

The synthesis of 2-sulfanyl-1,2-dihydro-naphthalen-1-ols is described. This methodology is based on rhodium catalysis and enables various thiols to undergo an asymmetric SN2' ring opening of oxabenzonorbornadiene. Under the reaction conditions ([Rh(COD)Cl](2) (2.5 mol %), (S)-(R)-PPF-P(t)Bu(2) (6 mol %), AgOTf (7 mol %), NH(4)I (1.7 equiv), galvinoxyl (5 mol %), THF, 85 degrees C), aryl- and alkyl-sulfide adducts are obtained in good to excellent yield and in high enantiomeric excess (>90% ee).     

Copper-catalyzed asymmetric ring opening of oxabicyclic alkenes with Grignard reagents

[reaction: see text] Simple Grignard reagents were applied in copper-catalyzed asymmetric ring-opening reactions of oxabenzonorbornadiene derivatives using spiro phosphoramidite ligands. Excellent anti-stereoselectivities and good enantioselectivities were achieved.     

Copper-catalyzed anti-stereocontrolled ring opening of oxabicyclic alkenes with grignard reagents

[reaction: see text] A general copper-catalyzed procedure for the stereoselective ring opening of [2.2.1]-oxabicyclic alkenes with Grignard reagents is described. In the presence of catalytic amounts of CuCl/PPh(3) the reaction occurs with very high or complete anti selectivity in all cases.     

Copper-catalyzed asymmetric ring opening of oxabicyclic alkenes with organolithium reagents

A highly efficient method is reported for the asymmetric ring opening of oxabicyclic alkenes with organolithium reagents. Using a copper/chiral phosphoramidite complex together with a Lewis acid (BF(3)·OEt(2)), full selectivity for the anti isomer and excellent enantioselectivities were obtained for the ring opened products.     

Rhodium-catalyzed asymmetric ring opening of oxabicyclic alkenes with organoboronic acids

The first rhodium(I)-catalyzed asymmetric addition of organoboronic acids to oxabicyclic alkenes is reported. This asymmetric ring-opening (ARO) reaction can proceed in high yield under very mild conditions with electronically diverse organoboronic acids, in a highly diastereoselective and enantioselective manner. [structure: see text]     

Fesulphos-palladium(II) complexes as well-defined catalysts for enantioselective ring opening of meso heterobicyclic alkenes with organozinc reagents

The air-stable and readily available cationic methyl palladium(II) complexes of planar chiral Fesulphos ligands [(Fesulphos)Pd(Me)(PhCN)]+ X- are highly efficient catalysts for the alkylative ring opening of oxa- and azabicyclic alkenes with dialkylzinc reagents, showing broad scope with regards to both the bicyclic substrate and the dialkylzinc reagent. Catalyst loading as low as 0.5 mol % is sufficient to achieve good yields and enantioselectivities ranging 94 --> 99% ee in most cases. {Fesulphos = (1-phosphino-2-sulfenylferrocene); X- = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate or PF6(-)].} The origin of the high asymmetric induction has been rationalized by mechanistic studies combining computational calculations and X-ray structural analysis.     

Palladium-catalyzed multistep reactions involving ring closure of 2-iodophenoxyallenes and ring opening of bicyclic alkenes

[reaction: see text] An efficient ring closure of 2-iodophenoxy-, 2-iodobenzyloxy-, and 2-iodobenzylaminoallenes followed by ring opening of oxabenzonorbornadienes leading to the synthesis of 2-benzofuranyl, 1H-isochromenyl, or 1,2-dihydroisoquinoline methyl-1,2-dihydro-1-naphthalenol derivatives catalyzed by palladium complexes is described.     

Iron-catalyzed regio- and stereoselective ring opening of [2.2.1]- and [3.2.1]oxabicyclic alkenes with a Grignard reagent

[reaction: see text] Arylative and alkenylative ring-opening reactions of a [2.2.1]- or [3.2.1]oxabicyclic alkene with a Grignard reagent take place in the presence of a catalytic amount of iron(III) chloride and a stoichiometric amount of TMEDA to produce a highly substituted 3-cyclohexen-1-ol or 3-cyclohepten-1-ol in good yield with high regio- and stereoselectivity.     

Copper phosphoramidite catalyzed enantioselective ring-opening of oxabicyclic alkenes: remarkable reversal of stereocontrol

[reaction: see text] An unprecedented copper phosphoramidite catalyzed enantioselective alkylative ring-opening reaction of oxabenzonorbornadiene derivatives with dialkylzinc reagents is reported. The reaction shows high levels of anti-stereoselectivity (up to anti/syn >99:1), complementary to the Pd(0)-catalyzed syn-selective ring-opening protocol, allowing a new entry to anti-dihydronaphthols with high enantioselectivity (up to 99% ee).     

Palladium-catalyzed regio- and enantioselective fluorination of acyclic allylic halides

This report describes the Pd(0)-catalyzed fluorination of linear allylic chlorides and bromides, yielding branched allylic fluorides in high selectivity. Many of the significant synthetic limitations previously associated with the preparation of these products are overcome by this catalytic method. We also demonstrate that a chiral bisphosphine-ligated palladium catalyst enables highly enantioselective access to a class of branched allylic fluorides that can be readily diversified to valuable fluorinated products.     

Rhodium-catalyzed asymmetric ring opening reactions of oxabicyclic alkenes: application of halide effects in the development of a general process

We have demonstrated halide effects in the rhodium-catalyzed asymmetric ring opening reaction of oxabicyclic alkenes. By employing halide and protic additives, the catalyst poisoning effect of aliphatic amines is reversed allowing the amount nucleophile to react in high yield and ee. Second, by simply changing the halide ligand on the rhodium catalyst from chloride to iodide, the reactivity and enantioselectivity of reactions employing an aromatic amine, malonate or carboxylate nucleophile are dramatically improved. Third, through the application of halide effects and more forcing reaction conditions, less reactive oxabicycle [2.2.1] substrates react to generate synthetically useful enantioenriched cyclohexenol products. Application of these new conditions to the more reactive oxabenzonorbornadiene permits the reaction to be run with very low catalyst loadings (0.01 mol %).     

氧杂双环烯烃开环反应的研究及其应用

有机金属试剂(其中包括镍、钯、铑、铁、铜)以及路易斯酸能选择性地催化氧杂双环烯烃的亲核开环反应,并建立多个手性中心。这种方法已经被用在一些生物活性分子的全合成过程当中,如甾体酮类似物等。     

Iridium-catalyzed asymmetric ring opening of azabicyclic alkenes by amines

The enantioselective ring-opening reactions of azabicyclic alkenes with primary and secondary aromatic amine nucleophiles are reported using an iridium catalyst generated in situ from 1.5 mol % of [Ir(COD)Cl](2) and 3 mol % of (S)-BINAP. The reaction affords the corresponding trans-1,2-diamine derivatives in moderate to good yields with moderate to high enantioselectivities (up to 97% ee). The trans-configuration of the 1,2-diamino product 2g was confirmed by X-ray crystallography.     

Palladium-catalyzed cross-coupling reactions of carboxylic anhydrides with organozinc reagents

[reaction: see text] Negishi-type cross-coupling reaction was effected by employing organozincs and anhydrides or mixed anhydrides that formed in situ from sodium salts of the corresponding acids and ethyl chloroformate under the catalysis of palladium(0). A general method for preparing symmetrical/unsymmetrical ketones was developed.     

Reactions of gem-difluoro-substituted organozinc reagents with propargyl halides

Russian Chemical Bulletin - gem-Difluoro-substituted organozinc reagents undergo cross-coupling reaction with propargyl halides in the presence of catalytic amounts of copper cyanide. The reaction...     

Copper catalyzed oxidation of organozinc halides

A wide range of organozinc substrates may be oxidized in the presence of catalytic copper to give carbon-carbon bonds in high yield.     

Hydrated nickel (II) halides mediated ring opening reaction with N-tosylaziridines

An efficient and water tolerant method for the synthesis ofβ-haloamines is described utilizing hydrated nickel（Ⅱ） halides （NiX₂ⅩnH₂O X = Cl,Br,I） and aziridines as starting materials.N-Tosylaziridines reacted with NiCl₂·6H₂O or NiI₂·6H₂O givingβ-chloro -orβ-iodoamines in high yields（73-99%） within a short time,but 10 mol%of n-Bu₄NBr should be added in the reactions of N-tosylaziridines with NiBr₂·3H₂O in order to obtain the high yields of correspondingβ-bromoamines.Solvent played an important role in the reactions.The proper solvent for the reaction of NiCl₂·6H₂O was DMF,while NiBr₂·3H₂O or NiI₂·6H₂O proceeded well in 1,4-dioxane.