Palladium-catalysed amination of 2-acyl-1-alkyl-5-bromopyrroles

The first intermolecular C-N bond-forming reactions between substituted 2-bromopyrroles and primary and cyclic secondary amines were performed using Pd₂(dba)₃ as catalyst with BINAP as the ligand. The aminations proceeded in the presence of NaO^tBu at 80-100 °C in 31-93% yields.     

A comparison of palladium complexes of BINAP and diphenylphosphinooxazoline ligands in the catalytic asymmetric synthesis of cis-decalins

BINAP and a range of oxazoline-containing phosphinamine ligands were screened in the palladium-catalysed asymmetric intramolecular Heck cyclisation to form cis-decalins. Complexes formed from Pd₂(dba)₃ and BINAP gave cyclised products in up to 65% yield and 85% ee. The t-leucine-derived diphenylphosphinoferrocenyloxazoline ligand afforded our optimal enantioselectivity of 85% for the range of phosphinamine ligands tested. Variation of solvent and base appears to indicate that this system is sensitive to catalyst deactivation and that a combination of either toluene or N-methylpyrrolidine with potassium carbonate as base was required for acceptable catalytic activity. Catalysts prepared from palladium complexes of diphenylphosphinoaryloxazoline ligands were less reactive than the corresponding BINAP catalysts as the optimal yield obtained was 47%.     

Asymmetric hydroformylation of vinyl acetate with BINAP–rhodium(I) complexes

Complexes of (R)-BINAP (BINAP=2,2′-bis(diphenylphosphino)-1,1′-binaphthyl) derived from the available rhodium precursors Rh(acac)(CO)₂ and [Rh(μ-OMe)(cod)]₂ are used for the asymmetric hydroformylation of vinyl acetate. Enantiomeric excesses of up to 60% are achieved with regioselectivities of up to 99%. Only a BINAP/Rh ratio of 2 is required. Effects of pressure and temperature on catalyst stability, enantio- and chemoselectivity are discussed.     

The regiochemistry of reduction of mono-ethyl fumarate and maleate using a ruthenium BINAP catalyst

The regiochemistry of the reduction of mono-ethyl fumarate using bis(carboxylato){2,2′-bis(diphenylphosphino)-[R]-1,1-binapthyl}-ruthenium(II) (Ru[BINAP]) in H₂/CH₃OD is reported and occurs opposite to the regiochemistry observed in the reduction of tiglic acid. Reduction of mono-ethyl maleate with D₂/CH₃OD is very sluggish but produces meso-dideuteriosuccinic acid with high stereoselectivity. Reduction of mono-ethyl maleate with Ru[BINAP](O₂CR)₂ and H₂/CH₃OD results in mono-ethyl succinate-d₁ with nearly complete loss of regiochemistry.     

Cationic iridium-BINAP complex-catalyzed addition of aryl ketones to alkynes and alkenes via directed C-H bond cleavage

Cationic Ir complex ([Ir(cod)₂]BF₄ + BINAP) catalyzed the addition of ortho-C-H bonds in aryl ketones to alkynes, which gave alkenylated products in good to high yield. Styrene derivatives were good substrates, and the enantioselective addition to norbornene was also described.     

Diastereoselective hydrogenation of folic acid esters with the Daniphos ligand

Folic acid dimethylester benzenesulfonate was hydrogenated homogeneously in a rhodium-catalyzed diastereoselective reaction employing a set of the previously published planar-chiral “Daniphos” ligands, which are based on an arene chromium tricarbonyl scaffold. Diastereoselectivities of up to 42% de were achieved, almost matching the benchmark ligand BINAP. An X-ray structure of the most successful ligand P(i-Pr₂)/PPh₂ is presented and discussed.     

Iridium‐Catalyzed Dehydrogenative Decarbonylation of Primary Alcohols with the Liberation of Syngas

A new iridium ‐ catalyzed reaction in which molecular hydrogen and carbon monoxide are cleaved from primary alcohols in the absence of any stoichiometric additives has been developed. The dehydrogenative decarbonylation was achieved with a catalyst generated in situ from [Ir(coe)₂Cl]₂ (coe=cyclooctene) and racemic 2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl (rac‐BINAP) in a mesitylene solution saturated with water. A catalytic amount of lithium chloride was also added to improve the catalyst turnover. The reaction has been applied to a variety of primary alcohols and gives rise to products in good to excellent yields. Ethers, esters, imides, and aryl halides are stable under the reaction conditions, whereas olefins are partially saturated. The reaction is believed to proceed by two consecutive organometallic transformations that are catalyzed by the same iridium(I)–BINAP species. First, dehydrogenation of the primary alcohol to the corresponding aldehyde takes place, which is then followed by decarbonylation to the product with one less carbon atom.     

New optically active organoantimony (BINASb) and bismuth (BINABi) compounds comprising a 1,1′-binaphthyl core: synthesis and their use in transition metal-catalyzed asymmetric hydrosilylation of ketones

Racemic 2,2′-bis[diarylstibano]-1,1′-binaphthyls [(±)-BINASbs] and 2,2′-bis[di(p-tolyl)bismuthano]-1,1′-binaphthyl [(±)-BINABi], which are the antimony and bismuth congeners of BINAP, have been prepared from 2,2′-dibromo-1,1′-binaphthyl (DBBN) via 2,2′-dilithio-1,1′-binaphthyl intermediate by treatment with the appropriate metal halides [(p-Tol)₂SbBr, Ph₂SbBr and (p-Tol)₂BiCl]. The optical resolution of the (±)-BINASbs could be achieved via the separation of a mixture of the diastereomeric Pd-complexes derived from the reaction of (±)-BINASbs with di-μ-chlorobis{(S)-2-[1-(dimethylamino)-ethyl]phenyl-C¹,N}dipalladium(II). Optically active (R)-BINASb and (R)-BINABi could be also obtained from optically active (R)-DBBN by the same procedure. The enantiopure BINASbs have been shown to be effective chiral ligands for the rhodium-catalyzed asymmetric hydrosilylation of ketones.     

BINAP versus BINAP(O) in asymmetric intermolecular Mizoroki-Heck reactions: substantial effects on selectivities

2,2′‐Bis(diphenylphosphino)‐1,1′‐binaphthyl (BINAP) was employed as chiral ligand in the enantioselective intermolecular Mizoroki–Heck reaction, whereas the use of cognate BINAP(O) (monooxidized BINAP) is unprecedented. The regio‐ and enantioselectivity of the arylation of representative cyclic alkenes changes dramatically in the presence of hemilabile BINAP(O) instead of BINAP. The arylation of 2,3‐dihydrofuran is perfectly regiodivergent (98:2 versus 0:100) and the arylation of cyclopentene is only enantioselective with BINAP(O) [60 versus 10 % enantiomeric excess (ee)]. Use of [Pd₂(dba)₃] ? dba (dba=dibenzylideneacetone) instead of Pd(OAc)₂ produces as high as 86 % ee in the arylation of cyclopentene.     

On the specific heat of nonstoichiometric ceria

Ceria (CeO₂) can readily be reduced to form a wide range of binary compounds CeO_y, 2 ≥y ≥ 1.5. Specific heat measurements at constanty were carried out for the composition range 2≥y > 1.714 and for the temperature range 300 K <T < 1200 K. In thisy,T region the specific heat exhibits a complex form reflecting various transformations. The results and theoretical evaluations of the specific heat are presented as the temperature is varied from low values (T ≈ 400K) where two phases coexist, through several phase transformations to a high temperature α phase. Special features of the specific heat due apparently to increased internal local pressure appearing for small deviations from stoichiometry are also discussed.     

Enantiomeric products formed via different mechanisms: asymmetric hydrogenation of an α,β-unsaturated carboxylic acid involving a Ru(CH3COO)2[(R)-binap] catalyst

Hydrogenation of (Z)-3-phenyl-2-butenoic acid with a Ru(CH₃COO)₂[(R)-binap] (BINAP=2,2′-bis(diphenylphosphino)-1,1′-binaphthyl) catalyst in methanol gives (S)-3-phenyl-2-butanoic acid and its R enantiomer in a 97:3 (4 atm) to 94:6 (100 atm) ratio in quantitative yield. Both hydrogen gas and protic methanol participate in the saturation of the olefinic bond. Analysis of the products obtained using (Z)-3-phenyl-2-butenoic acid-3-¹³C and either H₂, a 1:1 H₂-D₂ mixture, or D₂ in CH₃OD indicates that several catalytic cycles are operative, showing different reactivity and stereoselectivity. The major S enantiomer was formed primarily by the standard Ru monohydride mechanism, whereas the minor R isomer is produced via more complicated routes.     

Probing the stereo‐electronic properties of cationic rhodium complexes bearing chiral diphosphine ligands by 103Rh NMR

¹⁰³Rh NMR represents a powerful tool to assess the global electronic and steric contribution of diphosphine ligands on [Rh(COD)(diphosphine)]⁺ complexes. In the case of DIOP, BINAP and MeDUPHOS, this approach proved to be more informative than classical CO‐stretching frequency measurements. After validation, this method has been extended to a set of seven diphosphines. ¹⁰³Rh NMR measurements on [Rh(COD)(diphosphine)]PF₆ lead to the following order of donor properties: dppe > MeBPE > MeDUPHOS > dppb > DIOP > BINAP > Tol‐BINAP. This trend has been validated by DFT in the case of DIOP, BINAP and MeDUPHOS. In conjunction, ³¹P NMR chemical shift has been shown to reflect the ring constraints of the Rh‐diphosphine scaffold. This contribution is a step towards a mechanistic investigation of the catalytic hydrogenation of unsaturated substrates by ¹⁰³Rh NMR and DFT. Copyright © 2010 John Wiley & Sons, Ltd.     

Translation of helical chirality from polymer into monomer: supramolecular polymerization of a chirality-memory molecule with an asymmetric Pd(II) complex

A chirality-memorizing saddle-shaped porphyrin (1_2H) with 3,5-dipyridylphenyl side arms at the opposite meso positions underwent supramolecular polymerization in CH₂Cl₂ with a chiral Pd(II) complex of 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (Pd^II(BINAP)), forming a ladder-shaped polymer (3_2H) with a prevailing one-handed helical chirality. When this polymer was poured into AcOH containing 1,3-bis(diphenylphosphino)propane (DPPP) as a decomplexing agent, 3_2H was depolymerized in a stereochemically retentive way to give optically active 1_2H, hydrogen-bonded with AcOH. Although a cyclodimeric reference of 3_2H, formed from 2_2H having two 3-pyridylphenyl meso substituents in conjunction with Pd^II(BINAP), behaved similar to 3_2H, the translation efficiency of helical chirality was lower than that in the case with 3_2H.     

Synthesis of chiral N,N′-disubstituted 1,2-benzenediamines from o-dibromobenzene

Palladium-catalyzed amination of o-dibromobenzene provided chiral N,N′-disubstituted 1,2-benzenediamines in good to excellent yields. The amination was executed stepwise and in one pot to give unsymmetrically and symmetrically substituted 1,2-benzenediamines. Incorporation of chiral primary amines was possible without racemization using catalytic Pd₂dba₃–BINAP.     

[RuCl2COD)]n: A simplified source of Ru(II)-catalysts for the asymmetric hydrogenation of functionalized ketones

A simplified procedure of enantioselective ruthenium-catalyzed hydrogenation of functionalized ketones using commercially available [RuCl₂(COD)]_n, (COD = cis,cis-cycloocta-1,5 diene) mixed with the chiral diphosphines (BINAP, MeO-BIPHEP, DuPHOS) is reported. Under these conditions, C-O groups were completely hydrogenated with excellent enantiomeric excesses (up to 99 %).     

Solid-phase synthesis of 2,6- and 2,7-diamino-4(3H)-quinazolinones via palladium-catalyzed amination

A new procedure for the solid-phase synthesis of 2,6- and 2,7-diamino-4(3H)-quinazolinones is described. The method involves coupling of 2,4,6- and 2,4,7-trichloroquinazoline to a solid support via benzyl alcohol type linkers, subsequent displacement of chlorine at C-2 then at the C-6 or C-7 positions by amines (Fig. 1) and the cleavage of the products from the resin. The palladium-catalyzed amination of C-6 and C-7 positions with a representative set of amines in the presence of 2-(di-t-butylphosphino)biphenyl (DTBPBP), P(t-Bu)₃ and 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (BINAP) ligands has been investigated. This method should prove to be a useful tool for constructing combinatorial libraries containing the 4(3H)-quinazolinone moiety.     

Copper-catalyzed asymmetric hydrosilylation of ketones using air and moisture stable precatalyst Cu(OAc)2·H2O

Air and moisture stable copper(II) salts can be used to catalyze the hydrosilylation of aromatic ketones. The combination of catalytic amounts of copper(II) acetate or copper(II) acetate monohydrate (Cu(OAc)₂·H₂O) and BINAP in the presence of organosilanes as the stoichiometric reducing agent generates an active catalyst for the reduction of ketones.     

Synthesis of diarylamines in the benzo[b]thiophene series bearing electron donating or withdrawing groups by Buchwald-Hartwig C-N coupling

Diarylamines in the benzo[b]thiophene series bearing electron donating or withdrawing groups, were prepared by Buchwald-Hartwig C-N coupling in moderate to high yields. The conditions used were Pd(OAc)₂ (3 mol%), BINAP as ligand (4 mol%) and Cs₂CO₃ as base (1.4 equiv.), in toluene at 100°C, being 6-bromo or amino benzo[b]thiophenes coupled, respectively, with substituted anilines or phenylbromides. The 6-aminobenzo[b]thiophene derivatives were also prepared by palladium catalyzed C-N coupling of the corresponding 6-bromo compounds with benzophenone imine, followed by acidic hydrolysis of the imino derivatives. When 4-nitrobromobenzene and 4-bromobenzonitrile were used as coupling components, triarylamines were also isolated in small amounts. The presence of a fluorine atom on the phenylbromide highly increases the diarylamine yields.     

Synthesis of 3-aminoaspartic acid derivatives from glycine precursors

3-Aminoaspartic acid derivatives 3 have been synthesized via stereoselective alkylation of α-acetyloxyglycine Schiff base 2 with the enolate of glycine anion equivalent 1 as a carbon nucleophile in the presence of Pd(OAc)₂ and BINAP at room temperature. High chemical yields and moderate stereoselectivities were observed. The enantiomeric excess of the dl diastereomer can be increased to 95% after a single recrystallization from isopropanol and hexanes.     

Conformationally Flexible Biphenyl‐phosphane Ligands for Ru‐Catalyzed Enantioselective Hydrogenation

Stereomutation of a BIPHEP/RuCl ₂ /diamine complex (shown schematically) is possible because of the conformational flexibilty of BIPHEP ligands. The result is an asymmetric activation in the Ru‐catalyzed hydrogenation of carbonyl compounds to optically active alcohols. Whereas a racemic BINAP/RuCl₂ complex with a chiral diamine activator gives a 1:1 mixture of two diastereomers, unequal amounts of the diastereomers can be produced from a BIPHEP/RuCl₂ complex and a chiral diamine. Ar=3,5‐dimethylphenyl, BINAP=2,2′‐bis(diphenylphosphanyl)‐1,1′‐binaphthyl, BIPHEP=2,2′‐bis(diarylphosphanyl)biphenyl.