Synthesis of hexacyclic parnafungin A and C models

A convergent, practical route to unstable hexacyclic parnafungin A and C models has been developed. Two iodoxanthones were prepared in four or five steps (33-50% overall yield). Suzuki-Miyaura coupling of the iodoxanthones with excess readily available 3-carbomethoxy-2-nitrophenyl pinacol boronate afforded the hindered highly functionalized 2-arylxanthones (53-58%) in the first key step. In the second key step, zinc reduction gave benzisoxazolinones that were treated with MsCl and then base to generate the unstable hexacyclic parnafungin A (13% overall yield for 8 steps) and C (8% overall yield for 9 steps) models. Analogously to the parnafungins, hexacyclic parnafungin C model decomposes to a phenanthridine with a half-life of 2 d in CDCl(3).     

Toward the synthesis of norzoanthamine: complete fragment assembly

The complex marine alkaloid norzoanthamine (2) was envisioned to be assembled from three key building blocks: the C1-C5 fragment A, the C6-C10 fragment B, and the C11-C24 fragment C. The synthesis of fragment A was achieved in 14 steps and 33% overall yield from (R)-gamma-hydroxymethyl-gamma-butyrolactone. Fragment B was made in two steps from PMB-protected 4-pentynol in 76% yield. The C11-C24 fragment C was made from (S)-carvone via (R)-isocarvone in 18 steps (6% overall yield). The convergent stereoselective synthesis of the entire carbon framework (C1-C24) of the target molecule was achieved via the following assemblage. Alkenyl iodide 20 derived from the C11-C24 fragment C was coupled to fragment B (C6-C10) through a high-yielding Stille coupling reaction of these two sterically very demanding coupling partners, affording the key Diels-Alder precursor 24. The intramolecular Diels-Alder reaction proceeded smoothly in excellent yield and diastereoselectivity, generating the tricyclic trans-anti-trans perhydrophenanthrene motif of norzoanthamine (C6-C24). The final fragment coupling between lithiated fragment A (C1-C5) and aldehyde 40 (C6-C24) has also been successfully accomplished affording the entire carbon framework of the natural product.     

A novel method for the preparation of diborane from aluminum,ethyl chloride,boron oxide and hydrogen

A novel method is described for the preparation of diborane from aluminum, ethyl chloride, boron oxide and hydrogen via three steps; deoxyalkylation of boron oxide, hydrogenation of triethylboron and liberation of diborane. The triethylboron was prepared from aluminum, ethyl chloride and boron oxide directly at 85–110°C in 88% yield, with aluminum trichloride as by-product in 95% yield. In the presence of triethylamine and a hydrogen pressure of 130 kg/cm², the triethylboron was hydrogenated at 200°C for 2 hours to produce borane-triethylamine complex in 92% yield. The borane-triethylamine complex was treated again at 80°C with the aluminum trichloride collected from the first step to liberate diborane in 94% yield. The overall reaction yield was 76%.     

Efficient Preparation of Alkaloids Polycarpine and Polycarpaurines A and C

An efficient method for the preparation of alkaloids polycarpine and polycarpaurines A and C via microwave‐assisted three‐step one‐pot reaction as the key step has been developed. This is the first report about the synthesis of polycarpaurines A and C. Starting from commercially available p‐methoxybenzaldehyde, polycarpine and polycarpaurine A were obtained over seven steps with 40 and 24 % overall yield, respectively. Polycarpine could convert to polycarpaurine C in 72% yield in the presence of NaHSO₃. The structure of polycarpine and polycarpaurines A and C was confirmed by ¹H NMR, ¹³C NMR, and HRMS.     

Enhanced solid-state metathesis routes to carbon nanotubes

Ignition of three solids creates multiwalled carbon nanotubes in seconds. A solid-state metathesis (exchange) reaction between hexachloroethane (C2Cl6) and lithium acetylide (Li2C2) with 5% cobalt dichloride (CoCl2) added as an initiator produces up to 7% carbon nanotubes, as observed via transmission electron microscopy. Using the concept that sulfur can promote nanotube growth, the reaction yield can be increased to 15% by switching to CoS as the initiator. The more readily available, inexpensive calcium carbide (CaC2) can be substituted for lithium acetylide while maintaining comparable yields. Switching initiators to FeS can be used to further enhance the yield. A systematic study of the C2Cl6/CaC2 reaction system indicates that a yield up to 25% can be realized by using 6% FeS as the initiator. Reaction temperatures for the C(2)Cl6/CaC2 system of up to 3550 degrees C are calculated using thermodynamic data assuming quantitative yield and adiabatic conditions.     

Structure reassignment and synthesis of Jenamidines A1/A2, synthesis of (+)-NP25302, and formal synthesis of SB-311009 analogues

The proposed structures of jenamidines A, B, and C (1-3) were revised to jenamidines A1/A2, B1/B2, and C (8-10). Jenamidines A1/A2 (8) were synthesized from activated proline derivative 43 by conversion to 26 in two steps and 50% overall yield. Acylation of 26 with acid chloride 38d gave 39d, which was deprotected with TFA and then mild base to give 8 in 45% yield from 26. (-)-trans-2,5-Dimethylproline ethyl ester (49) was prepared by the enantioselective Michael reaction of ethyl 2-nitropropionate (51) and methyl vinyl ketone (50) using modified dihydroquinine 60 as the catalyst. Further elaboration converted 49 to natural (+)-NP25302 (12). A Wittig reaction of proline NCA (76) with ylide 79 gave 72 as a 9/1 E/Z mixture in 27% yield, completing a one-step formal synthesis of SB-311009 analogues.     

Chiral diols: a new class of additives for direct aldol reaction catalyzed by L-proline

Nine C2 symmetric diols have been examined as additives in the L-proline-catalyzed direct aldol reaction with significant improvement in enantioselectivity, conversion efficiency, and yield. Loading of 1 mol % of (S)-BINOL leads to the desired products in up to 98% ee and 90% yield. A transition state is proposed.     

Synthesis of N-benzylidenebenzylamine from benzylamine under the action of iron-containing catalysts in CCl4

A direct synthesis of N-benzylidenebenzylamine from benzylamine in the presence of iron-containing catalysts was performed with the 92?C96% yield. The reaction proceeds in tetrachloromethane at 80?C85°C over 8 h.     

Enantioselective total synthesis of (+)-gliocladine C: convergent construction of cyclotryptamine-fused polyoxopiperazines and a general approach for preparing epidithiodioxopiperazines from trioxopiperazine precursors

A concise second-generation total synthesis of the fungal-derived alkaloid (+)-gliocladin C (11) in 10 steps and 11% overall yield from isatin is reported. In addition, the epipolythiodioxopiperazine (ETP) natural product (+)-gliocladine C (6) has been prepared in six steps and 29% yield from the di-(tert-butoxycarbonyl) precursor of 11. The total synthesis of 6 constitutes the first total synthesis of an ETP natural product containing a hydroxyl substituent adjacent to a quaternary carbon stereocenter in the pyrrolidine ring.     

Biomimetic synthesis of the tetracyclic core of berkelic acid

Acid-catalyzed condensation of 2,6-dihydroxybenzoic acid 3 with ketal aldehyde 14 in methanol at 25 degrees C, followed by CH2N2 esterification, gave a 4:1:4:1 mixture of diastereomers 15b-18b in 60% yield. Equilibration of this mixture with TFA in CDCl3 provided tetracycle 15b (83% yield) with the complete skeleton of berkelic acid. A similar condensation at 0 degrees C afforded 15b-18b and a reduction product 19b, which was probably formed by a 1,5-hydride shift.     

Studies on Oxidative Coupling of Methane Catalysed by Li-Ce-Sr Oxides

The conditions for catalyst preparation and coupling reaction of methane were investigated. The experimental results showed that under the catalysts the selectivity for C2 formation may reach 98.5% and the yield 28.2% (the average within the first 30 minutes). A stale selectivity and yield for C2 formation obtained after reaction for 2h were 48.4% and 20.6%, respectively. Some kinetic parameters were also determined, including activation energy and the partial pressure dependence of the catalytic reaction rates. Finally a preliminary explanation of the reaction mechanism is suggested.     

Platinum-catalyzed intramolecular hydroamination of unactivated olefins with secondary alkylamines

Reaction of benzyl-2,2-diphenyl-4-pentenylamine with a catalytic 1:2 mixture of [PtCl2(H2C=CH2)]2 (2.5 mol %) and PPh3 in dioxane at 120 degrees C for 16 h led to isolation of 1-benzyl-2-methyl-4,4-diphenylpyrrolidine in 75% yield. A number of gamma- and delta-amino olefins underwent intramolecular hydroamination to form the corresponding pyrrolidine derivatives in moderate to good yield. The reaction displayed excellent functional group compatibility and low moisture sensitivity.     

Convenient synthesis of chiral H4-BINOL via direct hydrogenation of BINOL

<正>A simple,highly effective hydrogenation of chiral BINOL to provide H_4-BINOL in multigram scale with good yield(up to 78% yield) was developed.A series of heterogeneous catalysts was tested in the hydrogenation;;the best result was obtained with 5%Pd/ C in EtOH under the H_2 pressure of 50 bar for 2 h.This method is a more useful method for practical synthesis of optically pure H_4- BINOL than other available methods.     

Direct catalytic asymmetric Mannich-type reaction of beta-keto phosphonate using a dinuclear Ni2-Schiff base complex

Direct catalytic asymmetric Mannich-type reactions of beta-keto phosphonates are described. A homodinuclear Ni 2-Schiff base complex promoted the reaction at 0 degrees C, giving beta-amino phosphonates in up to 90% yield, 20:1 dr, and 99% ee. Control experiments suggested that two Ni metals are important for achieving high yield and stereoselectivity.     

Mono- and dialkylations of pyrrole at C2 and C5 positions by nucleophilic substitution reaction in ionic liquid

[reaction: see text] A novel ionic liquid methodology for pyrrole C-alkylation is described. The pyrrole alkylation is achieved with various simple alkyl halides and mesylates selectively at C2 and C5 positions in good yields with minimal byproducts under relatively mild conditions in various ionic liquids. 2-(3-Phenylpropyl)pyrrole (2a) was synthesized from pyrrole and 1-bromo-3-phenylpropane in a mixture solvent system, [bmim][SbF6] and CH3CN, in 81% yield at 115 degrees C for 44 h with 5% yield of dialkylated compound 3a.     

Stereoselective synthesis of optically active alpha-hydroxy ketones and anti-1,2-diols via asymmetric transfer hydrogenation of unsymmetrically substituted 1,2-diketones

[reaction: see text] A well-defined chiral Ru catalyst RuCl(N-(p-toluenesulfonyl)-1, 2-diphenylethylenediamine)(eta(6)-arene) effectively promotes asymmetric transfer hydrogenation of 1-aryl-1,2-propanedione with HCOOH/N(C(2)H(5))(3), leading preferentially to optically active 1-aryl-2-hydroxy-1-propanone with up to 99% ee and 89% yield at 10 degrees C. The reaction at 40 degrees C gives anti-1-aryl-1, 2-propanediol with up to 95% ee and 78% yield. This is a highly efficient procedure for the synthesis of optically active anti-diols.     

Efficient synthesis of isogranulatimide C, an analogue of the marine G2 checkpoint inhibitor alkaloid isogranulatimide

A three-step procedure to isogranulatimide C starting with the thermal condensation of 3-chloroindole with imidazole and proceeding in 41% yield is described.     

2-羟基-3,4,6-三甲氧基查尔酮的合成

本文开发了一种天然产物2-羟基-3,4,6-三甲氧基查尔酮(1)的十克级规模快速合成方法.通过改良合成2-羟基-3,4,6-三甲氧基苯甲醛(7)的甲基化和甲酰化条件,将7的合成总收率从文献报道的22％提高至68％.并以7为原料在乙腈为溶剂、80℃加热的条件下通过Wittig反应在50mmol规模以85％的收率合成了产物...     

Synthesis of (+)-patulolide C via an asymmetric hydroformylation/macrocyclization cascade

A highly atom-economical total synthesis of (+)-patulolide C has been accomplished in three steps from the known (2R)-8-nonyn-2-ol in 49% overall yield and 93% de. A Rh(I)-catalyzed asymmetric hydroformylation (AHF)/ intramolecular Wittig olefination cascade was utilized to set the C4-hydroxyl stereochemistry and E-olefin geometry as well as form the macrolactone.     

Stille-Heck coupling sequences applied in a versatile new access to steroid skeletons

A variety of enantiomerically pure steroidal compounds was synthesized utilizing a sequence of Stille and Heck cross-coupling reactions and subsequent thermal 6pi-electrocyclizations. Highly chemoselective Stille couplings on the triflate moiety of several 2-bromocyclohex-1-enyl triflates with cis- and trans-fused bicyclo[4.3.0]nonenylstannanes furnished the corresponding tricyclic bromobutadienes in good to excellent yields (70-97%). These were subjected to Heck reactions with tert-butyl acrylate to provide pentasubstituted tricyclic 1,3,5-hexatrienes. A significant increase in efficiency could be achieved by applying a novel protocol with a precatalyst on the basis of the palladacycle prepared from Pd(OAc)2 and P(o-Tol)3 with added triarylphosphines as co-ligands (73-90% yield). Upon heating to 205-215 degrees C in decalin or to 140 degrees C in toluene (for certain cases), these hexatrienes yielded (78-90%) various unsaturated steroid analogues as single diastereomers. A particular oxohexatriene, obtained after deprotection of an adjacent carbonyl group, underwent 6pi-electrocyclization at the unusually low temperature of 140 degrees C to yield (75%) an interesting 7-carboxyl-substituted steroidal dienone. Attempts to remove the remaining protecting groups from some of the other new steroidal compounds under acidic conditions furnished a novel 3-oxo-7-carboxyl steroid analogue and a 3-hydroxy-substituted steroidal diene. A novel estradiol derivative could be obtained in 69% yield from the synthesized steroidal dienone. Deprotection furnished the corresponding unprotected 7-carboxylestradiol in 81% yield.