丙烯酸聚醚聚氨酯合成反应中的氢键效应及其反应动力学研究

以红外光谱法研究了丙烯酸聚醚聚氨酯合成反应(其中有氢键效应存在)及其反应动力学。结果表明:由于丙烯酸聚氨酯分子链结构中含有-CO-O-;-NH-和-O-三种主要极性基因,导致在反应中存在明显的氢键变化。在第一步聚氨酯预聚体合成中,氢键距离R随反应进行而逐渐减小,反映出-NHCO-O-结构增加,聚集加强,氢键作用加强,并趋向稳定;其中不同结构聚氨酯预聚体氢键距离R不同:R_(MDI)>R_(HDI)>R_(TDP),链段结构中有序程度依次降低。在第二步丙烯酸聚氨酯合成中,存在明显键效应,其链段结构中有序程度较原来预聚体稳定或略有下降。在二步合成反应过程中,1/1-P_(NCO)和t之间呈现很好的线性关系,表明这两步合成均属二级反学动力学。其区别在于第一步反应速率常数(k_1)较第二步反应速率常数(k_2)小一个数量级。     

14C-labeled and large-scale synthesis of the angiotensin-(1-7)-receptor agonist AVE 0991 by cross-coupling reactions

The synthesis of (14)C-labeled AVE 0991 ((14)()C-1a) and large-scale synthesis of AVE 0991 (1a) are described. In the key step of the synthesis, the C-C coupling reaction of the imidazole (2) and thiophene (3) building blocks was studied under Suzuki and Stille reaction conditions, respectively. Suzuki reaction gave only moderate yields, whereas the best results were obtained under Stille reaction conditions with up to 64% yield.     

An efficient and simple aminobenzannulation reaction: pyrrolidine as a trigger for the synthesis of 1-amino-acridines

[reaction: see text] A new aminobenzannulation methodology has been developed and applied successfully to the synthesis of 1-amino-acridines. The key and last step goes through an enamine intermediate that was detected in some cases. When pyrrolidine and powdered 4 A molecular sieves were used, the enamine synthesis and the aminobenzannulation step took place subsequently, whereas for other secondary amines, neutral Al(2)O(3) or PtCl(2) catalysis was necessary.     

Mechanistic approaches to asymmetric synthesis of aziridines from guanidinium ylides and aryl aldehydes

To approach more realistic mechanisms for asymmetric aziridine synthesis from guanidinium ylides and aryl aldehydes, reactions were systematically carried out by using a variety of p-substituted benzaldehydes under modified conditions. Two kinds of reaction mechanisms controlled by the nature of the p-substituents of aryl aldehydes is proposed for the two-steps aziridine synthesis composed of a C-C bond formation by nucleophilic addition of guanidinium ylides to aryl aldehydes (step 1) and the fragmentation of intermediate adducts to aziridine products by intramolecular nucleophilic substitution (step 2). A S_Ni-like mechanism via cationic-like transition state is proposed for step 2 in the asymmetric synthesis using EDG-substituted benzaldehydes, whereas with EWG-substituted benzaldehydes, a S_N2-like mechanism is proposed. Hammett analysis, based on the diastereomeric ratio in the aziridine products, is consistent with the proposed rate-determining steps in these two mechanisms. A second Hammett analysis, based on the enantiomeric ratio of the aziridine products, clearly reveals the difference in the susceptibilities to the electronic substituents effect between step 1 and step 2.     

Synthesis and characterization of different types of epoxide-based Mannich polyols from low-cost cashew nut shell liquid

Cashew nut shell liquid (CNSL) is a natural aromatic organic oil consisting of phenolic compounds with interesting structures. Extraction of CNSL was performed in a Soxhlet apparatus. The major (90 %) component of CNSL is anacardic acid, which is easily decarboxylated to cardanol (10 %) by use of conventional methods. In this paper we describe a three-step synthesis of Mannich polyols for rigid foams. The first step is synthesis of N-(2-hydroxyethyl)-1,3-oxazolidine (the Mannich precursor) by condensation of paraformaldehyde and diethanolamine. The second step involves synthesis of the Mannich base phenolic ring of cardanol by reaction with N-(2-hydroxyethyl)-1,3-oxazolidine. The third step is alkoxylation. The synthesized polyols were characterized by FTIR and ¹H NMR spectroscopy and thin-layer chromatography.     

Synthesis of (S,S)-isodityrosine by Dötz benzannulation

[reaction: see text] A synthesis of (S,S)-isodityrosine 1, a naturally occurring, key structural subunit of numerous biologically active macromolecules, is described. A formal [3 + 2 + 1] cycloaddition (D?tz benzannulation) approach was utilized to simultaneously construct an aromatic ring and the diaryl ether linkage in one step. This key step was extended to the synthesis of (S,S)-isodityrosine in two separate convergent synthetic routes. This method demonstrates a novel and mild method for the synthesis of diaryl ethers.     

New methodology for the synthesis of thiobarbiturates mediated by manganese(III) acetate

A three step synthesis of various thiobarbiturate derivatives 17-24 was established. The first step is mediated by Mn(OAc)?, in order to generate a carbon-carbon bond between a terminal alkene and malonate. Derivatives 1-8 were obtained in moderate to good yields under mild conditions. This key step allows synthesis of a wide variety of lipophilic thiobarbiturates, which could be tested for their anticonvulsive or anesthesic potential.     

Total Synthesis of (+)-Lactacystin

A double stereodifferentiating crotylation between aldehyde 1 and silane (S)- 2 to afford homoallylic alcohol 3 is the key diastereoselective step (anti:syn >30:1) in an efficient asymmetric synthesis of (+)-lactacystin. This compound is a metabolite isolated from Streptomyces sp. OM-6519 that exhibits significant neurotrophic activity. An additional important step in the synthesis is a catalytic asymmetric aminohydroxylation used as the key step in the synthesis of the (2R,3S)-hydroxyleucine synthon.     

(±)-麝香酮和(R)-麝香酮的自由基扩环合成法

以环十二酮为原料, 经自由基扩环反应, 合成(±)-麝香酮和(R)-麝香酮, 总收率分别为51%和32%。     

Synthesis of all low-energy stereoisomers of the tris(pyrrolidinoindoline) alkaloid hodgkinsine and preliminary assessment of their antinociceptive activity

The previously unknown stereoisomers 3, 4, ent-1, and ent-4 of the tris(pyrrolidinoindoline) alkaloids hodgkinsine (1) and hodgkinsine B (2) were prepared by stereocontrolled total synthesis. In each synthesis, a catalyst-controlled intramolecular Heck reaction was the key step in appending a third cis-pyrrolidinoindoline ring to a hexacyclic chimonanthine precursor. Results of the preliminary evaluation of these hodgkinsine stereoisomers in the tail flick and capsaicin pain models are reported.     

Synthesis of maremycins A and D1 via cycloaddition of a nitrone with (E)-3-ethylidene-1-methylindolin-2-one

A concise synthesis of maremycins A and D1 has been accomplished via cycloaddition of a chiral cyclic nitrone with ( E)-3-ethylidene-1-methylindolin-2-one as a key step. This synthesis clarifies the stereochemistry of the maremycins and is suitable for large-scale synthesis for biological screening.     

1-苯基-3-甲基-6-N,N-二正丁基胺-2(1H)-喹喔啉-2-酮的全合成

报道了2(1H)-喹喔啉类衍生物——1-苯基-3-甲基-6-N,N-二正丁基胺-2(1H)-喹喔啉-2-酮的全合成.该化合物及其中间体1-苯基-3-甲基-6-胺基-2(1H)-喹喔啉-2-酮和1-苯基-3-甲基-6-硝基-2(1H)-喹喔啉-2-酮均为新化合物,文中给出了它们的重要的分析数据,简要讨论了溶剂在关环反应以及N-烷基化反应中的重要影响,偶然发现以水作溶剂时关环主产物为1-苯基-3-甲基-5-硝基-苯并咪唑.这类化合物可应用于药物,如用作N-甲基-D-天冬氨酸(NMDA)受体及α-氨基羟甲基异噁唑丙酸(AMMPA)受体拮抗剂、杀菌剂等;还可用作植物生长抑制剂、荧光探针以及作为新型功能染料中间体等诸多领域.     

Titanium(II)-mediated cyclizations of (silyloxy)enynes: a total synthesis of (-)-7-demethylpiericidin A1

A concise total synthesis of 7-demethylpiericidin A1 has been completed. The synthesis features a titanium(II)-mediated cyclization of a (silyloxy)enyne as the key step and proceeds in nine steps from tiglic aldehyde.     

Total synthesis of (+)-alpha-onocerin in four steps via four-component coupling and tetracyclization steps

A remarkably short (four steps, 31% overall yield) enantioselective synthesis of the structurally unique C2-symmetric tetracyclic triterpene (+)-alpha-onocerin (1) has been developed. The brevity of this mechanism depends on the assembly of four fragments (two molecules of a chiral epoxy ketone and two molecules of vinyllithium) to generate the chiral bis-epoxide 4 in one step, and on the efficient formation of all four carbocyclic rings in one step by cation-olefin tetracyclization. New and general methodology for the conversion of vinyl tert-butyldimethylsilyl ethers to vinyl triflates with retention of E or Z olefinic geometry also was utilized in the synthesis of 1. A short enantioselective synthesis of a non-C2-symmetric diastereomer of 1 is also described which uses the new methodology.     

维生素A衍生物合成工艺的改进

维生素A衍生物合成工艺的改进;多双键烷基膦衍生物;Wittig-Horner反应     

Stereoselective synthesis of (1R,3S)- -chrysanthemic acid through microbiological reduction of 2,2,5,5-tetramethyl 1,4-cyclohexanedione.

An efficient, highly stereoselective synthesis of (1 ,3 )- -chrysanthemic acid 6 is described. The crucial step of this synthesis was the microbiological reduction of dione 1 into ( )-ketol 2.     

Revisiting a classic approach to the Aspidosperma alkaloids: an intramolecular Schmidt reaction mediated synthesis of (+)-aspidospermidine

[reaction: see text] A total synthesis of (+)-aspidospermidine (1) is described. The key reactions used in the synthesis of this pentacyclic Aspidosperma alkaloid were a deracemizing imine alkylation/Robinson annulation sequence, a selective "redox ketalization", and an intramolecular Schmidt reaction. A Fischer indolization step carried out on a tricyclic ketone mirrored the sequence reported by Stork and Dolfini in their classic aspidospermine synthesis.     

Cascade enantioselective synthesis of γ-aryl-γ-butyrolactones with a delayed stereoselective step

Enantioselective synthesis of γ-aryl-γ-butyrolactones is achieved using (S)-1-phenylethylamine as a chiral auxiliary. The synthesis involves cascade formation-destruction-formation of the chiral centre with a delayed stereoselective step. The actual stereoselective step has been found to be intramolecular nucleophilic attack on a diastereotopic carbocation formed, thereby resulting in the formation of non-racemic γ-aryl-γ-butyrolactones.     

Conversion of carbon dioxide to propionaldehyde over cobalt and rhodium nanoparticles supported on MIL-53 (Al) metal–organic framework

The two-step conversion of carbon dioxide to propionic acid and propionaldehyde has been studied in the presence of novel catalysts, cobalt and rhodium nanoparticles supported on MIL-53(Al) microporous metal–organic framework. The first step is hydrogenation of carbon dioxide with formation of synthesis gas over cobalt-containing catalyst Co/MIL-53(Al) (500°C, 1 atm), and the second step is continuous (without separation) Rh/MIL-53 (Al)-catalyzed hydroformylation of ethylene with the synthesis gas formed in the first step.     

Synthesis of 1alpha-hydroxyvitamin D5 using a modified two wavelength photolysis for vitamin D formation

[reaction: see text] 1Alpha-hydroxyvitamin D5 (1) is a promising chemopreventive agent for breast cancer and is being developed as a drug. We report a synthesis for this vitamin D analogue which uses a photochemical method for the B-ring opening, leading to the conjugated triene system. The precursor 7-dehydrositosteryl acetate (4) obtained through a one-pot, five-step procedure, was completely free of the 4,6-diene isomer that usually forms in the 5,7-diene synthesis. The pre-vitamin isomer (11) was generated using a modified two-wavelength photolysis procedure that increases the yield for this step more than 3-fold compared to classically used photolysis. The 1alpha-hydroxylation step was performed on the 3-triethylsilyl-trans-vitamin D5 (17) obtained via the sulfur dioxide adduct of cis-vitamin D5, in an overall yield of 48%. Photoisomerization and deprotection completed the synthesis.