Stereoarrayed CF3‐Substituted 1,3‐Diols by Dynamic Kinetic Resolution: Ruthenium(II)‐Catalyzed Asymmetric Transfer Hydrogenation

CF₃‐substituted 1,3‐diols were stereoselectively prepared in excellent enantiopurity and high yield from CF₃‐substituted diketones by using an ansa‐ruthenium(II)‐catalyzed asymmetric transfer hydrogenation in formic acid/triethylamine. The intermediate mono‐reduced alcohol was also obtained in very high enantiopurity by applying milder reaction conditions. In particular, CF₃C(O)‐substituted benzofused cyclic ketones underwent either a single or a double dynamic kinetic resolution during their reduction.     

Highly Productive CNN Pincer Ruthenium Catalysts for the Asymmetric Reduction of Alkyl Aryl Ketones

Chiral pincer ruthenium complexes of formula [RuCl(CNN)(Josiphos)] ( 2 – 7 ; Josiphos=1‐[1‐(dicyclohexylphosphano)ethyl]‐2‐(diarylphosphano)ferrocene) have been prepared by treating [RuCl₂(PPh₃)₃] with (S,R)‐Josiphos diphosphanes and 1‐substituted‐1‐(6‐arylpyridin‐2‐yl)methanamines (HCNN; substituent=H ( 1 a ), Me ( 1 b ), and tBu ( 1 c )) with NEt₃. By using 1 b and 1 c as a racemic mixture, complexes 4 – 7 were obtained through a diastereoselective synthesis promoted by acetic acid. These pincer complexes, which display correctly matched chiral PP and CNN ligands, are remarkably active catalysts for the asymmetric reduction of alkyl aryl ketones in basic alcohol media by both transfer hydrogenation (TH) and hydrogenation (HY), achieving enantioselectivities of up to 99 %. In 2‐propanol, the enantioselective TH of ketones was accomplished by using a catalyst loading as low as 0.002 mol % and afforded a turnover frequency (TOF) of 10⁵–10⁶ h^?1 (60 and 82 °C). In methanol/ethanol mixtures, the CNN pincer complexes catalyzed the asymmetric HY of ketones with H₂ (5 atm) at 0.01 mol % relative to the complex with a TOF of ≈10⁴ h^?1 at 40 °C.     

Photochemical Synthesis of Highly Functionalized Cyclopropyl Ketones

A series of di‐ and trisubstituted cyclopropyl ketones 11 were prepared by irradiation of ketones 3 and 5 , which bear a leaving group adjacent to the carbonyl C‐atom. The required ketones 3 could be easily synthesized either by functionalization of ketones 1 with a hypervalent iodine reagent, 2 , or by O‐sulfonylation of α‐hydroxy ketones 7 . The nitrates 5 were obtained by treatment of the corresponding α‐bromo ketones with AgNO₃. The irradiation of 3 and 5 must be performed in the presence of an acid scavenger (1‐methyl‐1H‐imidazole) to obtain the cyclopropanes 11 in good yields. The synthetic efficiency of the method was, among other things, demonstrated by the preparation of a highly strained bicyclo[2.1.0]pentane 11i in good yield. The mechanism of the photochemical cyclization was investigated by means of photokinetic measurements, as well as by quantum‐chemical calculations. It was shown that the presence of the leaving group substantially influences all steps of the photochemical reaction cascade. The X‐ray crystal structures of 11j and exo‐ 11k were also determined.     

Synthesis and stereoselectivity of a new type of unsaturated phosphonates

A series of unsaturated phosphonates 2, 3, 4 with structures similar to that of abscisic acid (ABA) were synthesized by the Wittig‐Horner reactions of bisphosphonylmethane 1 with β‐substituted propenals, propargyl aldehydes or α,β‐unsaturated methyl ketones. Compounds 5 were prepared by the Michaelis‐Becker reactions of ω‐bromodienes 7 with sodium phosphites. Compounds 7 were obtained by the phase transfer Wittig reactions of ω‐bromobutylphosphonium salt 6 with β‐substituted propenals. The structures of all new compounds prepared were characterized by ¹H NMR, ³¹P NMR, IR spectra, and elemental analysis or MS. The stereochemistry of the Wittig reactions was studied. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:261–266, 2000     

Chiral Primary‐Amine‐Catalyzed Conjugate Addition to α‐Substituted Vinyl Ketones/Aldehydes: Divergent Stereocontrol Modes on Enamine Protonation

Enantioselective protonation with a catalytic enamine intermediate represents a challenging, yet fundamentally important process for the synthesis of α‐chiral carbonyls. We describe herein chiral primary‐amine‐catalyzed conjugate additions of indoles to both α‐substituted acroleins and vinyl ketones. These reactions feature enamine protonation as the stereogenic step. A simple primary–tertiary vicinal diamine 1 with trifluoromethanesulfonic acid (TfOH) was found to enable both of the reactions of acroleins and vinyl ketones with good activity and high enantioselectivity. Detailed mechanistic studies reveal that these reactions are rate‐limiting in iminium formation and they all involve a uniform H₂O/acid‐bridged proton transfer in the stereogenic steps but divergent stereocontrol modes for the protonation stereoselectivity. For the reactions of α‐branched acroleins, facial selections on H₂O‐bridged protonation determine the enantioselectivity, which is enhanced by an OH???π interaction with indole as uncovered by DFT calculations. On the other hand, the stereoselectivity of the reactions with vinyl ketones is controlled according to the Curtin–Hammett principle in the C? C bond‐formation step, which precedes a highly stereospecific enamine protonation.     

Synthesis of Thieno[2,3‐b]quinolinone Derivatives

The Knoevenagel reactions of malononitrile with acetophenone or 4‐substituted acetophenons were carried to give the corresponding 2‐(1‐aryle thylidene)malononitriles, which was further cyclized with sulfur using NaHCO₃ as catalysts to generate 2‐amino‐5‐arylthiophene‐3‐carbonitrile 2 . The intermediate enamines 3 were prepared by refluxing of 2 with 5‐substituted‐1,3‐cyclohexanedione using p‐toluenesulfonic acid as catalyst. The title compounds 4‐amino‐3‐aryl ‐7‐substituted‐7,8‐dihydrothieno[2,3‐b]quinolin‐5(6H)‐one were synthesized by cyclization of 3 in the presence of K₂CO₃ and Cu₂Cl₂. The structures of all compounds were characterized by elemental analysis, IR, MS, and ¹H‐NMR spectra.     

Direct Amination and Synthesis of Fused N‐Substituted Isothiochromene Derivatives

Isothiochromene[3,4‐d] pyrimidine derivatives 2 , 3 , and 4a , b were synthesized from the reaction of 3‐amino‐1‐(pyridin‐4‐yl)‐5‐(pyridin‐4‐ylmethylene)‐5,6,7,8‐tetrahydro‐1H‐isothiochromene‐4‐carbonitrile 1 with acetic anhydride, formamide, urea, or thiourea in appropriate experimental conditions. Combination of 1 with carbon acid derivatives afforded isothiochromene [3,4‐b]pyridine 6 – 8 in good yield. A simple approach for N‐substituted fused isothiochromene derivatives has been explored. A POCl₃‐mediated direct amination of isothiochromene amide 2 with NH₂‐heterocycles, secondary amines, and carbohydrazides is described and compared with classical method, yielding 10 – 14 . The structures of the newly synthesized compounds were elucidated on the basis of elemental analysis, and spectral data.     

Development of general methods for the synthesis of new substituted allyl bromides as promising alkenylating agents

A general procedure has been developed for the synthesis of hitherto unknown substituted allyl bromides. The procedure includes preparation of the corresponding α,β-unsaturated carboxylic acid esters from accessible ketones according to the Horner-Emmons reaction, reduction of these esters with diisobutylaluminum hydride to allylic alcohols, and substitution of the hydroxy group by bromine by the action of PBr₃. The E,Z isomer ratio of the synthesized unsaturated compounds ranges from 3: 1 to 4: 1.     

Novel Approach for Rapid and Efficient Synthesis of 2‐(3‐(4‐Aryl)‐1‐isonicotinoyl‐4,5‐dihydro‐1H‐pyrazol‐4‐yl)‐3‐phenylthiazolidin‐4‐one Derivatives and Screened Their Antimicrobial Activity

A series of compounds, viz. 2‐(3‐(4‐aryl)‐1‐isonicotinoyl‐4,5‐dihydro‐1H‐pyrazol‐4‐yl)‐3‐phenylthiazolidin‐4‐one 4 ( a – n ), have been synthesized by reaction of 3 ( a – n ) with thioglycolic acid in the presence of zinc chloride. Compounds 3 ( a – n ) have been synthesized by amination of formylated pyrazoles 2 ( A – B ), which were synthesized by formylation of 1 ( A – B ) by Vilsmeier–Haack reagent (POCl₃/DMF). Compounds 1 ( A – B ) were synthesized by condensation of hydrazide and substituted acetophenones under conventional method and microwave irradiation method. These compounds were identified on the basis of melting point range, Rf values, infrared, ¹H NMR, and mass spectral analysis. These compounds were evaluated for their in vitro antimicrobial activity, and their minimum inhibitory concentration was determined. Among them, compound 4b and compound 4l possess appreciable antimicrobial and antifungal activities. Antibacterial activity results showed that compounds containing electron‐withdrawing groups were more active than compounds containing electron‐releasing groups.     

Asymmetric synthesis of new chiral long chain alcohols

Sixteen new chiral alcohols with alkyl (C₁₁–C₁₉) and aryl, substituted aryl, hetero aryl and biaryl groups 2a–2t were synthesized by three different asymmetric reduction methods from their corresponding ketones 1a–1t. Chiral NaBH₄ (method A), chiral BH₃ (method B) and chiral AIP (method C) were used as asymmetric reduction catalysts. Chiral NaBH₄ was modified by four different ligands 3a–3d, chiral BH₃ and chiral AIP by four different ligands 4a–4d. Ligand 4c was synthesized for the first time in this work. Chiral NaBH₄ generated chiral alcohols of (R)-configuration and chiral BH₃ and chiral AIP of (S)-configuration with high enantiomeric excesses, were analysed by chiral HPLC. In order to determine the ee values by chiral HPLC, sixteen corresponding racemic alcohols, synthesized by reducing their corresponding ketones via NaBH₄, were used for chiral resolution on a Daicel OD HPLC column. The sixteen starting ketones were synthesized in this study by Friedel–Craft acylation. The new chiral alcohols were characterized by IR, NMR, (¹H and ¹³C), MS, elemental analyses and specific rotation. The reduction methods A, B and C were applied to these ketones for the first time in this study and were compared with each other. The relationship between the structure of the ketone and the yield and the enantiomeric excess was discussed.     

Synthesis of three carbon atom bridged 2,4‐diaminopyrrolo[2,3‐d]‐pyrimidines as nonclassical dihydrofolate reductase inhibitors

A series of seven nonclassical three carbon atom bridged 2,4‐diamino‐5‐substituted‐pyrrolo[2,3‐d]‐pyrirnidines 1a‐g were synthesized as potential inhibitors of dihydrofolate reductase. Selective oxidation of diols 7a‐g affords α‐hydroxy ketones 8a‐g. Subsequent condensation with malononitrile gave the requisite 2‐amino‐3‐cyano‐4‐substituted furan precursors 9a‐g. Cyclocondensation with guanidine in refluxing ethanol in one step affords the three carbon atom bridged 2,4‐diamino‐5‐substituted‐pyrrolo[2,3‐d]‐pyrimidines 1a‐g. Preliminary biological results indicated that these compounds showed moderate inhibitory activities against dihydrofolate reductases from Pneumocystis carinii, Toxoplasma gondii, Mycobacterium avium and rat liver with IC₅₀ values in the 0.66 μM ‐ 70.1 μM range and some compounds had marginal selectivity for T. gondii dihydrofolate reductase.     

Synthesis and Characterization of 11‐Amino‐3‐methoxy‐8‐substituted‐12‐aryl‐8,9‐dihydro‐7H‐chromeno[2,3‐b]quinolin‐10(12H)‐one Derivatives

A series of 2‐amino‐7‐methoxy‐4‐aryl‐4H‐chromene‐3‐carbonitrile compounds 2 were obtained by condensation of 3‐methoxyphenol with β‐dicyanostyrenes 1 in absolute ethanol containing piperidine. The intermediate enamines 3 were prepared by compounds 2 with 5‐substituted‐1,3‐cyclohexanedione using p‐toluenesuflonic acid (TsOH) as catalyst. The title compounds 11‐amino‐3‐methoxy‐8‐substituted‐12‐aryl‐8,9‐dihydro‐7H‐chromeno[2,3‐b]quinolin‐10(12H)‐one 4 were synthesized by cyclization of the intermediate enamines 3 in THF with K₂CO₃ /Cu₂Cl₂ as catalyst. The structures of all compounds were characterized by elemental analysis, IR, MS, and ¹H NMR spectra. The crystal structure of compound 4i was determined by single‐crystal X‐ray diffraction analysis.     

Design,Synthesis and Antitumor Activity of Asymmetric Bis(s‐triazole Schiff‐base)s Bearing Functionalized Side‐Chain

1‐Amino‐2‐pyrid‐3‐yl‐5‐(2‐benzoylethylthio)‐s‐triazole ( 1 ) was condensed with 1‐amino‐3‐mercapto‐5‐ [(un)substituted phenyl]‐s‐triazoles and subsequently substituted with chloroacetic acid to afford bis‐s‐triazole sulfanylacetic acid mono‐Schiff bases ( 3a – 3e ), which were condensed with 9‐formylanthracene to produce asymmetric bis(s‐triazole Schiff base) sulfanylacetic acids ( 4a – 4e ). The structures of new synthesized compounds were characterized by elemental analysis and spectral data, and their in vitro antitumor activity against L1210, CHO and HL60 cell lines was evaluted via the respective IC₅₀ values by methylthiazole trazolium (MTT) assay.     

Convenient and Efficient Synthesis of 11‐Amino‐2,8‐substituted‐2,3,8,9‐tetrahydrobenzo[4,5]thieno[2,3‐b]quinolinone Derivatives

The Gewald reactions of 5‐substituted‐1,3‐cyclohexanedione, malononitrile, and powdered sulfur were carried out to give the corresponding products 2‐amino‐5‐substituted‐7‐oxo‐4,5,6,7‐tetrahydrobenzo[b]thiophene‐3‐carbonitrile derivatives 1 . The intermediate enamines 2 were prepared by reaction of compounds 1 and 5‐substituted‐1,3‐cyclohexanedione with hydrochloric acid as catalyst. The title compounds 11‐amino‐2,8‐substituted‐2,3,8,9‐tetrahydrobenzo[4,5]thieno[2,3‐b]quinolinone 3 were synthesized by cyclization of compounds 2 in the presence of K₂CO₃ and Cu₂Cl₂. The structures of all compounds were characterized by elemental analysis, IR, MS, and ¹H‐NMR spectra.     

Synthesis of α‐(Fluorophenyl)pyridine by Palladium‐Catalyzed Cross‐Coupling Reaction

A series of α‐(fluoro‐substituted phenyl)pyridines have been synthesized by means of a palladium‐catalyzed cross‐coupling reaction between fluoro‐substituted phenylboronic acid and 2‐bromopyridine or its derivatives. The reactivities of the phenylboronic acids containing di‐ and tri‐fluoro substituents with α‐pyridyl bromide were investigated in different catalyst systems. Unsuccessful results were observed in the Pd/C and PPh₃ catalyst system due to phenylboronic acid containing electron‐withdrawing F atom(s). For the catalyst system of Pd(OAc)₂/PPh₃, the reactions gave moderate yields of 55% –80%, meanwhile, affording 10% –20% of dimerisation (self‐coupling) by‐products, but trace products were obtained in coupling with 2,4‐difluorophenylboronic acids because of steric hinderance. Pd(PPh₃)₄ was more reactive for boronic acids with sterically hindering F atom(s), and the coupling reactions gave good yields of 90% and 91% without any self‐coupling by‐product.     

Pd(0)‐Catalyzed Tandem One‐Pot Reaction of Biphenyl Ketones/Aldehydes to the Corresponding Di‐substituted Aryl Olefins

Synthesis of di‐substituted aryl olefins via a Pd(0)‐catalyzed cross‐coupling reaction of biphenyl ketones/aldehydes, tosylhydrazide, and aryl bromides (or benzyl halides) was developed. This methodology was achieved by one‐pot two‐step reactions involving the preparation of N ‐tosylhydrazones by reacting tosylhydrazide with biphenyl ketones/aldehydes, followed by coupling with aryl bromides (or benzyl halides) in the presence of Pd(PPh₃ )₄ and lithium t ‐butoxide to produce various di‐substituted aryl olefins in moderate to good yields.     

Platinum‐Catalyzed Multi‐Step Reaction of Propargyl Alcohols with N‐Heteroaromatics

N‐Methyl indole reacts with but‐2‐yn‐1‐ol in the presence of PtCl₂ in MeOH giving indole derivatives having a substituted 3‐oxobutyl group at the 3‐position in good yield. Under the reaction conditions, various substituted indoles and substituted propargyl alcohols are successfully involved in the reaction giving the corresponding addition products in good to moderate yields. The catalytic reaction can be further extended to N‐phenyl pyrrole. In the present multi‐step reaction, PtCl₂ likely plays dual roles: as the catalyst for the rearrangement of propargyl alcohols to the corresponding alkenyl ketones and as the catalyst for the addition of indoles to the alkenyl ketones. Experimental evidence is provided to support the proposed mechanism.     

Cs2CO3-catalyzed alkylation of indoles with trifluoromethyl ketones

A Cs₂CO₃-catalyzed alkylation reaction of indoles with trifluoromethyl ketones was presented. Both alicyclic and aromatic trifluoromethyl ketones as well as various substituted indoles are compatible with the methodology. Good to excellent yields of the corresponding trifluoromethyl substituted tertiary alcohols 2,2,2-tritrifluoro-1-(1H-indol-3-yl)-ethan-1-ols were acquired as the sole products.     

A Simple Synthesis of Polyfunctionalized 4‐Aminopyrazolidin‐3‐ones as ‘Aza‐deoxa’ Analogs of D‐Cycloserine

A simple five‐step synthesis of fully substituted (4RS,5RS)‐4‐aminopyrazolidin‐3‐ones as analogs of D ‐cycloserine was developed. It comprises a two‐step preparation of 5‐substituted (4RS,5RS)‐4‐(benzyloxycarbonylamino)pyrazolidin‐3‐ones, reductive alkylation at N(1), alkylation of the amidic N(2) with alkyl halides, and simultaneous hydrogenolytic deprotection/reductive alkylation of the primary NH₂ group. The synthesis enables an easy stepwise functionalization of the pyrazolidin‐3‐one core with only two types of common reagents, aldehydes (or ketones) and alkyl halides. The structures of products were elucidated by NMR spectroscopy and X‐ray diffraction.     

Synthesis of Some Novel Phenyl Substituted Oxothiazolidin- 1’’,3’’,4’’-thiadiazolo-[3’,4’-b]thiazoline of 3β-Substituted Cholestane

Three title compounds 4a—4c have been synthesized by the cyclodehydration of 1’-benzylidine-4’-(3β-substituted-5α-cholestane-6-yl)thiosemicarbazones 2a—2c with thioglycolic acid followed by the treatment with cold conc. H2SO4 in dioxane. The compounds 2a—2c were prepared by condensation of 3β-substituted-5α-cholestan- 6-one-thiosemicarbazones 1a—1c with benzaldehyde. These thiosemicarbazones 1a—1c were obtained by the reaction of corresponding 3β-substituted-5α-cholestan-6-ones with thiosemicarbazide in the presence of few drops of conc. HCl in methanol. The structures of the products have been established on the basis of their elemental, analytical and spectral data.