Ring closure of 2‐N‐benzylamino‐3‐aroylpropionic acids ( 3 ) with acetic anhydride afforded 3‐N‐benzylamino‐5‐aryl‐2(3H)‐furanones ( 4 ). The reaction of the furanones ( 4 ) with benzylamine in benzene was found to be time dependent. Thus refluxing the reaction mixture for 1 h only afforded the open‐chain amides ( 5a‐c ). When the reaction was conducted for 3 h the 2(3H)‐pyrrolones ( 6 ) were obtained. Hydrazine hydrate affected ring opening of the furanones to give the hydrazides ( 5d‐f ). Also, semicarbazide converted ( 4 ) into the corresponding semicarbazide derivatives ( 5g‐i ). The hydrazides ( 5d‐f ) were reacted with benzoyl chloride to give the corresponding diaroylhydrazines ( 5j‐l ). The open‐chain derivatives ( 5 ) were converted into a variety of heterocycles: isothiazolones ( 7 ), dihydropyridazinones ( 8 ), 1,3,4‐oxadiazoles ( 9 ) and 1,2,4‐triazole derivatives ( 10 ) via cyclization reactions. 相似文献
In this communication, polyanionic poly(potassium 3‐sulfopropyl methacrylate) (PSPM) brushes were switched from hydrophilic to hydrophobic by exchange of the counter cations. First, poly(potassium 3‐sulfopropyl methacrylate) brushes were grown by means of atom transfer radical polymerization (ATRP) from thiol monolayers of initiating ω‐mercaptoundecyl bromoisobutyrate and mixed monolayers of thiol initiator and 1‐undecanothiol (blank thiol) attached to gold surfaces. The kinetics of the polymerization reaction were followed by means of the quartz microbalance technique with dissipation (QCM‐D). The collapse of PSPM brushes in the presence of cationic surfactants like quaternary ammonium salts (tetraethylammonium bromide, hexadecyltrimethylammonium bromide) and imidazolium salts (1‐dodecyl‐3‐methylimidazolium bromide, 1H,1H,2H,2H‐perfluoro‐1‐decyl‐3‐methylimidazolium bromide) was shown by QCM‐D. Water contact angle measurements proved that the wettability of the surface could be tuned reversibly from hydrophilic values (<30 °) to hydrophobic ones (>85 °).
Three different routes were probed for the synthesis of enantiomerically enriched 2‐(1‐aminoethyl)phenols and their methyl ethers. The first route centers on diastereoselective nucleophile addition to chiral imines. The second route has as key steps the enantioselective reduction of a ketone followed by nucleophilic substitution, and the third route involves a diastereoselective imine reduction. The efficiency of the approach depends on the substrate substitution pattern. All three methods work well for the parent compound 2‐(1‐aminoethyl)phenol ( 1 ) but the third route is the most efficient, providing the compound with >96% enantiomer excess in three steps with an overall yield of 71%. Conversely, for the ortho‐methyl analogue 2 , the first method is best. For the t‐Bu‐substituted analogue 3 , only moderate enantiomeric enrichment was achieved. 相似文献
The first catalytic asymmetric inverse‐electron‐demand (IED) oxa‐Diels–Alder reaction of ortho‐quinone methides, generated in situ from ortho‐hydroxybenzyl alcohols, has been established. By selecting 3‐methyl‐2‐vinylindoles as a class of competent dienophiles, this approach provides an efficient strategy to construct an enantioenriched chroman framework with three adjacent stereogenic centers in high yields and excellent stereoselectivities (up to 99 % yield, >95:5 d.r., 99.5:0.5 e.r.). The utilization of ortho‐hydroxybenzyl alcohols as precursors of dienes and 3‐methyl‐2‐vinylindoles as dienophiles, as well as the hydrogen‐bonding activation mode of the substrates met the challenges of a catalytic asymmetric IED oxa‐Diels–Alder reaction. 相似文献
The incorporation of a specific cleavage site into an oligodeoxynucleotide can be achieved by utilizing the four 5′‐S‐(4,4′‐dimethoxytrityl)‐2′‐deoxy‐5′‐thionucleoside 3′‐(2‐cyanoethyl diisopropylphosphoramidites) 5 and 15a – c (Fig. 1). Based on the silver ion assisted cleavage of P? S and C? S bonds, we synthesized oligodeoxynucleotides with an achiral 5′‐phosphorothioate linkage 3′–O–P–S–5′ by the solid‐phase phosphoramidite procedure. The efficient cleavage of these modified oligodeoxynucleotides can be detected by HPLC, PAGE, and surface plasmon resonance (SPR) spectrometry. The liberated 5′‐thiol moiety can be used directly for post‐reaction labeling with appropriately functionalized reporter groups. 相似文献
Extremely high enantioselectivity (>99.5% ee) and chemical yield (>99%) are achieved in an asymmetric autocatalytic reaction. A (5‐pyrimidyl)alkanol with a tert‐butylethynyl group at its 2‐position ( 1 ) is a very efficient asymmetric autocatalyst in the enantioselective alkylation in Equation (1). 相似文献
Asymmetric transfer hydrogenation was applied to a wide range of racemic aryl α‐alkoxy‐β‐ketoesters in the presence of well‐defined, commercially available, chiral catalyst RuII–(N‐p‐toluenesulfonyl‐1,2‐diphenylethylenediamine) and a 5:2 mixture of formic acid and triethylamine as the hydrogen source. Under these conditions, dynamic kinetic resolution was efficiently promoted to provide the corresponding syn α‐alkoxy‐β‐hydroxyesters derived from substituted aromatic and heteroaromatic aldehydes with a high level of diastereoselectivity (diastereomeric ratio (d.r.)>99:1) and an almost perfect enantioselectivity (enantiomeric excess (ee)>99 %). Additionally, after extensive screening of the reaction conditions, the use of RuII‐ and RhIII‐tethered precatalysts extended this process to more‐challenging substrates that bore alkenyl‐, alkynyl‐, and alkyl substituents to provide the corresponding syn α‐alkoxy‐β‐hydroxyesters with excellent enantiocontrol (up to 99 % ee) and good to perfect diastereocontrol (d.r.>99:1). Lastly, the synthetic utility of the present protocol was demonstrated by application to the asymmetric synthesis of chiral ester ethyl (2S)‐2‐ethoxy‐3‐(4‐hydroxyphenyl)‐propanoate, which is an important pharmacophore in a number of peroxisome proliferator‐activated receptor α/γ dual agonist advanced drug candidates used for the treatment of type‐II diabetes. 相似文献
N‐Boc ketimines derived from pyrazolin‐5‐ones were explored to develop an unprecedented domino aza‐Friedel–Crafts/N,O‐acetalization reaction with 2‐naphthols. The novel method requires a catalyst loading of only 0.5 mol % of a bifunctional squaramide catalyst, is scalable to gram amounts, and provides a new series of furanonaphthopyrazolidinone derivatives bearing two vicinal tetra‐substituted stereogenic centers in excellent yields (95–98 %) and stereoselectivity (>99:1 d.r. and 97–98 % ee ). A different reactivity was observed in the case of 1‐naphthols and other electron‐rich phenols, which led to the aza‐Friedel–Crafts adducts in 70–98 % yield and 47–98 % ee . 相似文献
The reaction of 2‐chloro‐4,5‐dihydroimidazole ( 5 ) with 2‐aminobenzohydrazides 6a–e led to the formation of 2‐amino‐N′‐(imidazolidin‐2‐ylidene)benzohydrazides as zwitterions 7a–e , which on treatment with carbon disulfide in the presence of triethylamine afforded 3‐(imidazolidin‐2‐ylideneamino)‐2‐thioxo‐2,3‐dihydroquinazolin‐4(1H)‐ones 8a–e . Compounds 8a–d were further converted into the corresponding 3‐(imidazolidin‐2‐ylideneamino)quinazoline‐2,4(1H,3H)‐diones 9a–d using hydrogen peroxide–sodium hydroxide solution. The structures of the compounds prepared were established by elemental analyses, IR and NMR spectra as well as X‐ray crystallographic analyses of 7e and 9a . 相似文献