Synthesis of BINOL derived phosphorodithioic acids as new chiral Brønsted acids and an improved synthesis of 3,3′-disubstituted H8-BINOL derivatives

Original phosphorodithioic acid diesters were prepared according to an improved synthesis of 3,3′-disubstituted H₈-BINOL derivatives. In preliminary experiments, these new Brønsted acids were tested as organocatalysts in three reactions. They promoted the Nazarov cyclisation with mixed selectivities, the Mannich reaction with good enantioselectivity and they catalyzed efficiently the alkylation of N-acyliminium with enol silyl ether.     

Synthesis of cholaphanes by ring closing metathesis

The synthesis of cholaphanes by ring closing metathesis (RCM) of 3α,7α,12α,24-tetraol allyl derivatives, obtained from cholic acid, was attempted. The reactions of tetraol 3,24-diallyl ether or 3,24-diacrylate were not satisfactory. However, diallyl derivatives of disteroidal 3,3′- or 24,24′-ortho-phthalates reacted smoothly affording cyclic dimers in good yields. In all the reactions studied, the E isomers of the macrocycles were obtained in excess.     

Three dimeric anthracene derivatives from the fruits of Bulbine abyssinica

From the fruits of Bulbine abyssinica three new dimeric anthracene derivatives, (P)-8,9,1′,8′-tetrahydroxy-3,3′-dimethyl[10,7′-bianthracene]-1,4,9′,10′-tetraone (trivial name abyquinone A), (10R)-1,4,8,1′,8′-pentahydroxy-3,3′-dimethyl-[10,7′-bianthracene]-9,9′,10′(10H)-trione (trivial name abyquinone B), and (10R)-3′,4′-dihydro-1,4,8,3′,8′,9′-hexahydroxy-3,3′-dimethyl-[10,7′-bianthracene]-9,1′(10H,2′H)-dione (trivial name abyquinone C) were isolated. Despite their structural differences, these three compounds are connected to each other by the apparently biomimetic conversion of abyquinone C (a preanthraquinonylanthrone with two stereogenic centers) into B (an anthraquinonylanthrone with one stereogenic center) and finally into A (an axially chiral bianthraquinone) under mild conditions, involving a highly efficient center-to-axis chirality transfer. In addition, the known anthraquinones islandicin and chrysophanol were identified. The structures were determined on the basis of spectroscopical evidences, chemical transformations, and quantum chemical CD calculations.     

Enantioselective construction of quaternary asymmetric carbon centers using an aldol reaction of trimethoxysilyl enol ethers catalyzed by lithium binaphtholate

An aldol reaction of 2,2-disubstituted trimethoxysilyl enol ethers with aldehydes catalyzed by a dilithium salt of (R)-3,3′-dichlorobinaphthol afforded the corresponding aldol adducts with quaternary carbon centers in high anti-selectivities (syn:anti = ∼1:50) and enantioselectivities (∼90% ee).     

Synthesis and structural characterization of novel bridged platinum(II) biscarbene complexes

Novel bridged platinum(II) biscarbene complexes are reported: 1,1′-dimethyl-3,3′-methylene-4-diimidazolin-2,2′-diylidene platinum(II) (3) and 1,1′-dimethyl-3,3′-ethylene-4-diimidazolin-2,2′-diylidene platinum(II) complexes 4 are directly accessible in high yields starting from platinum halides. The one-pot synthesis obviates the need for multi-step reactions via metal precursors or free carbenes. An X-ray crystal structure of 1,1′-dimethyl-3,3′-methylene-4-diimidazolin-2,2′-diylidene platinum(II) dibromide (3b) confirmed the structural similarity to the known corresponding palladium complexes. Since free 1,1′-di-R-3,3′-methylene-4-diimidazolin-2,2′-diylidenes are only available in low yields this synthetic route provides an easy access to the corresponding carbene complexes.     

Dibutylphosphate (DBP) mediated synthesis of cyclic N,N′-disubstituted urea derivatives from amino esters: a comparative study

The N,N′-disubstituted urea derivatives such as amino acid hydantoins and dihydrouracil derivatives were prepared starting from natural and unnatural amino acid esters using dibutylphosphate (DBP). During the attempted synthesis of N-heterocycles with larger than six-membered rings containing the N,N′-disubstituted urea functionalities, three unexpected products namely squamolone, N-methyl pyrrolidine-2-one, and diketopiperazine were isolated.     

Reaction, identification, and fluorescence of aminoperfluorophenazines

Perfluorophenazine regiospecifically reacted with monoalkyl-, dialkyl-, and arylamines to afford the corresponding 2-amino-substituted derivatives. 2-(Ethylamino)- and 2-(diethylamino)perfluorophenazine reacted with another molar amount of ethylamine and diethylamine to preferentially provide the 2,7-disubstituted derivatives, respectively. Perfluoro(2,7-dimethylphenazine) was allowed to react with ethylamine to give the 1-ethylamino derivative. These regiospecific reactions were explained by the density functional theory (DFT) calculations. Perfluorophenazine reacted with ethylenediamine to afford the 2,3-cyclized and N,N′-bis(2-perfluorophenazinyl) derivatives. These amino-substituted products showed UV-vis absorption (λ_max) and fluorescence maxima (F_max) in the range of 439-536 and 524-613 nm in hexane, respectively. Some of them exhibit intense fluorescence.     

Synthesis of chiral 3,3′-disubstituted 1,1′-binaphthyl-2,2′-disulfonic acids

A convenient synthesis of chiral 3,3′-disubstituted 1,1′-binaphthyl-2,2′-disulfonic acids (BINSA, 1) was developed. The key was directed ortho-lithiation of BINSA methyl ester 2 with n-BuLi and subsequent reaction with an electrophile. Electrophiles such as Br₂, I₂, Me₃SiOTf, and i-PrOB(Pin) reacted smoothly with 3,3′-dilithiated BINSA methyl ester, and the corresponding 3,3′-dihalo-, 3,3′-bis(trimethylsilyl)-, and 3,3′-diboryl-BINSA derivatives were obtained in yields of 21–78%. This simple synthetic method is highly attractive since the ability to prepare 3,3′-disubstituted BINOLs in advance can be useful.     

Synthesis, complexation behavior and application of a new diphosphite ligand in rhodium-catalyzed hydroformylation

Oxidative coupling of 3-(3-tert-butyl-4-hydroxyphenyl)propionic acid methyl ester (2) gave dimethyl 3,3′-(5,5′-di-tert-butyl-6,6′-dihydroxybiphenyl-3,3′-diyl)-dipropionate (1c), which upon phosphorylation/transesterification with a phosphochloridite derived from (R)-binaphthol, formed the new unsymmetrical binaphthol-bridged diphosphite 4. A rhodium catalyst based on 4 as ligand gave predominantly iso-selectivity in the hydroformylation of selected styrenes but opposite regioselectivity with 2,6-disubstituted derivatives. New chelate metal complexes (acac)RhL, PdCl₂L and PtCl₂L have been synthesized by reacting 4 with (acac)Rh(CO)₂, PdCl₂(MeCN)₂ and PtCl₂(COD), respectively. The structure of obtained compounds is determined based on ¹H, ¹³C, ³¹P and ¹⁹⁵Pt NMR spectroscopy and mass spectrometry data.     

Efficient synthesis of 3,3′,5,5′-tetra(p-X-phenylethynyl)biphenyl (X: NMe2; OMe) by homocoupling of 1-bromo-3,5-di(p-X-phenylethynyl)benzene or by heterocoupling of 3,3′,5,5′-tetraethynylbiphenyl with p-X-phenylbromobenzene with nickel or palladium complexes, respectively

The conjugated 3,3′,5,5′-tetra(p-X-phenylethynyl)biphenyl derivatives were efficiently obtained by homocoupling of 1-bromo-3,5-di(p-X-phenylethynyl)benzene mediated by zero-valent nickel complexes.The 1-bromo-3,5-di(p-X-phenylethynyl)benzene was previously prepared by heterocoupling between 1-bromo-3,5-di(ethynyl)benzene and p-X-iodobenzene (X: NMe₂; OMe) catalysed by the palladium/copper system in good yield. The necessary 1-bromo-3,5-di(ethynyl)benzene was obtained by heterocoupling between 1,3,5-tribromobenzene and 2-methyl-3-butyn-2-ol catalysed by palladium and successive treatment with sodium hydroxide in dry toluene, in good yield.The same 3,3′,5,5′-tetra(p-X-phenylethynyl)biphenyl (X: NMe₂; OMe) derivatives were alternatively synthesised in highest yield by heterocoupling between 3,3′,5,5′-tetra(ethynyl)biphenyl and p-X-bromobenzene (X: NMe₂; OMe) catalysed by palladium in excellent yields. Previously, 3,3′,5,5′-tetra(ethynyl)biphenyl was obtained in practically quantitative yield by homocoupling of 1-bromo-3,5-di[4-(2-methyl-3-butyn-2-ol)] benzene mediated by the zero-valent nickel complex to the 3,3′,5,5′-tetra{di[4-(2-methyl-3-butyn-2-ol)]}biphenyl followed the treatment with sodium hydroxide.     

1,1′-Methylene-bis(1,1′,2,2′,3,3′,4,4′-octahydroisoquinoline): synthesis, reaction, resolution, and application in catalytic enantioselective transformations

The preparation of new chiral 1,3-diamine ligand systems based on the 1,1′-methylene-bis(1,1′,2,2′,3,3′,4,4′-octahydroisoquinoline) framework is described. Synthesis of various mono-, di-, and bridged N-alkyl derivatives are presented. Resolution of one compound, its Cu(I)Br X-ray crystallographic structure and the preliminary results on its application in the enantioselective Henry and Aldol reactions are disclosed.     

A concise approach to CF3-containing furan-3-ones, (bis)pyrazoles from novel fluorinated building blocks based on 2,3-butanedione

1,1,1-Trifluoro-4,5,5-trimethoxyhex-3-en-2-one and lithium (2Z)-1,1,1-trifluoro-5,5-dialkoxy-4-oxohex-2-en-2-olate were synthesized for the first time via direct trifluoroacetylation of 2,3-butanedione acetal derivatives. A simple and effective approach to acetal or acyl substituted CF₃-pyrazoles, 5,5′-bis(trifluoromethyl)-3,3′-bipyrazole, and, to 5-trifluoromethylfuran-3-ones is presented.     

Synthesis, structural characterization and electrochemical study of 1,1′-ferrocenylene labeled amino acids

Unsymmetrical 1,1′-disubstituted ferrocenes bearing an amino acid moiety and a conjugated electron density controlling substituent were synthesized conveniently starting from 1,1′-ferrocenedicarbaldehyde. The novel ferrocene amino acid derivatives were completely characterized from their MS, ¹H NMR and ¹³C NMR spectra. Their electrochemical behavior was studied by cyclic voltammetry. Their formal redox potentials E_f were slightly influenced by the nature of the amino acid and mainly by the kind of the ethenyl substituent. Furthermore all the (Z)-isomers exhibited a slight anodic shift compared with the corresponding (E)-isomers.     

A novel,chemoselective one-pot procedure for the preparation of 3H-spiro[isobenzofuran-1,2′-pyrrole]-3,3′(1′H)-dione derivatives via oxidative cleavage of 3a,8b-dihydroxyindeno[1,2-b]pyrroles

A one-pot, efficient and chemoselective procedure for the synthesis of new 3H-spiro[isobenzofuran-1,2′-pyrrole]-3,3′(1′H)-dione derivatives has been developed which involves room temperature oxidative cleavage of 3a,8b-dihydroxyindeno[1,2-b]pyrroles themselves synthesized from the reaction of ninhydrin and enaminones in 30% ethanol. A reasonable mechanism is proposed for the oxidation reaction based on the results of this study and our previous related work.     

A new route to 2,2′,3,3′-tetrasubstituted binaphthyls

Based on an ortho-lithiation protocol of 2,2′-dibromo-1,1′-binaphthyl four tetrasubstituted binaphthyls, 2,2′-dibromo-3,3′-diiodo-, 3,3′-dibromo-2,2′-diiodo-, 2,2′,3,3′-tetrabromo-, and 2,2′,3,3′-tetraiodo-1,1′-binaphthyls have been prepared in excellent yield which in turn proved to be versatile key intermediates in the synthesis of various 2,2′,3,3′-tetrasubstituted 1,1′-binaphthyl derivatives.     

Synthesis of novel 3′-spirocyclic-oxindole derivatives and assessment of their cytostatic activities

The synthesis of some novel 3′-spirocyclic-oxindole compounds, based on the spiro[indole-3,5′-isoxazolidin]-2(1H)-one, the 2′H-spiro[indole-3,6′-[1,3]oxazinane]-2,2′(1H)-dione and the 2′H-spiro[indoline-3,3′-pyrrolo[1,2-c][1,3′]oxazine]-1′,2(1H)-dione heterocyclic structures, is described. These compounds were prepared from methyl α-(2-nitrophenyl)acrylate via [1,3]-dipolar cycloaddition reactions with two acyclic nitrones and one cyclic nitrone followed by reduction of the cycloadducts and then treatment with triphosgene. Two of these compounds showed significant cytostatic activity on three cancer cell lines with GI₅₀ values of 2.6-4.1 μM on the human breast cancer cell line, MCF-7.     

Synthesis of new compounds containing the 2,3-dihydro[1,4]dioxino[2,3-b]pyridine heterocyclic system as a substructure

2,3-Dihydro-spiro[1,4]dioxino[2,3-b]pyridine-3,3′-pyrrolidine (8A) and 2,3-dihydro-spiro[1,4]dioxino[2,3-b]pyridine-3,4′-piperidine (9A) have been synthesized from 2-chloro-3-pyridinol. The corresponding 2,3′ (8B) and 2,4′ (9B) isomers were obtained via the Smiles rearrangement, while 9B was also selectively synthesized from 2-nitro-3-pyridinol. The separation of the isomers A and B under the sulfamide form was carried out by flash column chromatography. Subsequent transformations of the corresponding dioxinopyridine derivatives were described.     

Four hydroxyls are better than two. The use of a chiral lithium salt of 3,3′-bis-methanol-2,2′-binaphthol as a multifunctional catalyst of enantioselective Michael addition reactions

The catalytic performance of the Li salt of (S)- or (R)-3,3′-bis[bis-(phenyl)hydroxymethyl]-2,2′-dihydroxy-dinaphthalene-1,1′ (BIMBOL) in asymmetric Michael additions of malonic acid derivatives and toluedine has been studied. Nitrostyrene and cyclohex-2-enone were chosen as Michael acceptors. Efficient asymmetric C-C and C-N bond formations with ee’s of up to 95% at room temperature were observed. A transition state model of the malonic ester addition to cyclohex-2-enone has been proposed based on the molecular structure of the acetone solvate of BIMBOL. The impact of the catalyst self-association on its performance is also discussed.     

New N-acyl, N-alkyl, and N-bridged derivatives of rac-6,6′,7,7′-tetramethoxy-1,1′,2,2′,3,3′,4,4′-octahydro-1,1′-bisisoquinoline

The preparation of potential new ligand systems based on the rac-1,1′,2,2′,3,3′,4,4′-octahydro-6,6′,7,7′-tetramethoxy-1,1′-bisisoquinoline skeleton has been investigated. Syntheses of N-(2-bromobenzyl), N-(3-acetoxybenzyl), N-acetyl, N-chloroacetyl, N-chlorocarbonyl, N-ethoxycarbonyl and N-tert-butyloxycarbonyl derivatives and five macrocyclic, polyether containing derivatives are described.     

One catalyst for two distinct reactions: sequential asymmetric hetero Diels-Alder reaction and diethylzinc addition

This paper describes the successful development of a series of chiral zinc catalysts containing (R)-3,3′-Br₂-BINOL ligand and various diimine activators for enantioselective HDA reaction of Danishefsky's diene with aldehydes through a combinatorial approach, affording the corresponding 2,3-dihydro-4H-pyran-4-one derivatives in excellent yields and enantioselectivities. The application of this type of catalysts was also extended to the diethylzinc addition to the benzaldehyde, affording the corresponding secondary alcohol with up to 94.5% ee under optimized conditions. On the basis of these facts, the integration of two distinct enantioselective reactions, HDA and diethylzinc addition reactions, has been realized in one-pot with the promotion of a single chiral zinc catalyst in a sequential manner. The impact of diimine additive on the catalytic system of HDA reaction was also investigated by probing the nonlinear effect of reaction system. The positive nonlinear effect exhibited in the catalytic system could be attributed to the poor solubility of the heterochiral zinc species. On the basis of various experimental findings disclosed in this research, a possible mechanism for the asymmetric induction in the 3,3′-Br₂-BINOL/Zn/diimine catalyzed enantioselective HDA reaction of Danishefsky's diene with aldehydes was outlined.